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learning and mastering procedural skills are major challenges in anesthesia practice and are essential in the process of achieving clinical competence .
anesthesiologists carry out many complex clinical tasks in their routine work which the trainee is expected to learn and master during training .
an increased public awareness of healthcare related issues has led to greater accountability of healthcare professionals .
this has very rightly led to an increasing focus on patient safety in clinical practice .
the supervisors have to undertake the important responsibility of deciding when a trainee can be allowed to perform the various procedures without direct supervision while ensuring patient safety .
supervisors and trainers must accept that not all trainees can be equally quick in learning and equally competent in performing practical procedures and reliable , and objective assessment is , therefore , mandatory .
airway management is an inherent part of the routine day - to - day work of anesthesiologists .
they are required to perform this procedure not only in the operation theater , but , also in the intensive care unit , the wards and the emergency department .
failure to perform the technique promptly and correctly can lead to serious consequences including death .
it is important to ensure that an anesthesia trainee is capable of performing tracheal intubation independently before he or she could be included in a cardiac arrest team , where direct supervision by a senior colleague is not always possible .
this requires robust and reliable assessment techniques such as direct observation by senior anesthesiologists using procedure - specific tools while the trainee is performing the procedure on actual patients . when constructing an assessment tool , it is important to explore the literature to see whether there is an already existing instrument that is appropriate and has established reliability and validity .
we were successful in retrieving tools for assessment of procedures performed by anesthesiologists , including rapid sequence induction of anesthesia and management of difficult airways .
however , we could not identify a structured tool for assessment of routine airway management with established reliability and validity .
the objectives of this study were to evaluate the inter - rater and test - retest reliability and construct validity of a tool designed to assess competence in bag - mask ventilation and tracheal intubation .
reliability of a tool is its ability to assess skills consistently by different assessors at different times while construct validity is the ability of the tool to differentiate among varying levels of expertise .
approval was granted by the university ethics review committee ( 1398-ane - erc-09 ) and written informed consent was obtained from all participants .
junior trainees were described as those having had more than two and < 4 months of anesthesia training , while senior residents recruited were those in the fourth year of training and already performing airway management independently .
the study protocol was presented in the departmental faculty meeting so as to share it with all faculty members .
the purpose of the study was explained to the participating residents at the time of informed consent .
the participants ' bag - mask ventilation and tracheal intubation skills were assessed by the use of a structured procedure - specific assessment tool .
all three authors participated in the construction of the tool and advice was taken from two other senior anesthesia consultants .
the tool comprised of five major categories with further sub - categories in each , in order to evaluate the performance of the trainee in all the essential steps involved in the procedure [ table 1 ] .
a simple 3-point scale was used to assess each step , where : steps of bag - mask ventilation and tracheal intubation assessed by direct observation in anesthesia trainees
1 ( one ) meant step not performed2 ( two ) meant performance below expectations3 ( three ) meant performance meets expectationsa column was added for steps not applicable during the performance .
1 ( one ) meant step not performed 2 ( two ) meant performance below expectations
3 ( three ) meant performance meets expectations a column was added for steps not applicable during the performance . performance below expectation was defined in the tool as unsuccessful attempt or incorrectly performed step , while meets expectation was defined as step performed adequately and successfully .
the procedural steps used for assessment of bag - mask ventilation and tracheal intubation skills are provided in table 1 . before finalizing the tool for the study
, we conducted a pilot study to identify any missing steps and to assess the practicality of using the tool in the operation theater .
the pilot study provided a chance for a final check on the content validity and served as a means of training the investigators in rating trainees ' performance by direct observation .
the authors also attended a half - day workshop on direct observation of procedural skills .
the residents were assessed while working in their assigned operation theater under the supervision of the assigned consultant anesthesiologist .
trainee 's assessment was not done if the patient being anesthetized was pregnant or had oral , faciomaxillary or neck pathology or anatomic anomaly , obesity ( body mass index > 30 ) , rheumatoid arthritis , ankylosing spondylitis , a history of difficult airway in the past or was found to have limited mouth opening , buck teeth , short thick neck with limited mobility , and mallampati grade iii or iv .
the assessment was done simultaneously by two of the investigators who are senior consultant anesthesiologists and registered supervisors for anesthesia training .
the trainee was observed while managing the airway with bag - mask ventilation and intubating the trachea with a tracheal tube .
the assessment time began once the patient was transferred to the operating table for induction of anesthesia and monitors were attached and ended when the endotracheal tube position was confirmed , and the tube was fixed . any decision to take over the procedure , in case
the trainee was unable to intubate the patient 's trachea , was left to the discretion of the supervising consultant .
it was planned to allow two attempts at laryngoscopy and intubation , and if the trainee was unsuccessful after two attempts , it was to be considered a failed attempt .
each resident was observed performing the same procedure again after 3 - 4 weeks by the same assessors to evaluate the test - retest reliability of the tool .
sample size was calculated using pass version 11 ( ncss llc , kaysville , utah ) . in a test for agreement between raters using the kappa statistic ,
a sample size of 20 subjects achieves 80% power to detect a true kappa value of 0.90 in a test of h0 : kappa = 0.50 versus h1 : kappa 0.50 using a two - tailed level of significance of 0.05 .
statistical analysis was performed using statistical packages for social sciences version 19 ( spss inc . ,
inter - rater and test - retest reliability were computed by percent agreement and kappa statistic .
kappa statistic was used to evaluate the level of agreement between assessors ' ratings and between the same assessor 's ratings at two points in time for each item of the structured assessment form .
kappa is positive when the agreement exceeds what is expected by chance ; kappa is negative when the observed agreement is less than the chance agreement . for the interpretation of kappa values
the rating indicators are : 0.0 - 0.2 slight agreement , 0.21 - 0.40 fair agreement , 0.41 - 0.60 moderate agreement , 0.61 - 0.80 substantial agreement , and 0.81 - 1.0 almost perfect or perfect agreement .
average agreement and the average kappa value was also calculated . for construct validity , the score of sub - categories of the main criteria were added for each rater in order to perform the analysis by using independent sample t - test and mann - whitney u - test ( as per rule of normality of the data ) to compare the scores between junior and senior residents .
statistical analysis was performed using statistical packages for social sciences version 19 ( spss inc . ,
inter - rater and test - retest reliability were computed by percent agreement and kappa statistic .
kappa statistic was used to evaluate the level of agreement between assessors ' ratings and between the same assessor 's ratings at two points in time for each item of the structured assessment form .
kappa is positive when the agreement exceeds what is expected by chance ; kappa is negative when the observed agreement is less than the chance agreement . for the interpretation of kappa values
the rating indicators are : 0.0 - 0.2 slight agreement , 0.21 - 0.40 fair agreement , 0.41 - 0.60 moderate agreement , 0.61 - 0.80 substantial agreement , and 0.81 - 1.0 almost perfect or perfect agreement .
average agreement and the average kappa value was also calculated . for construct validity , the score of sub - categories of the main criteria were added for each rater in order to perform the analysis by using independent sample t - test and mann - whitney u - test ( as per rule of normality of the data ) to compare the scores between junior and senior residents .
the inter - rater agreement between scores at the two assessments is presented in table 2 .
percent agreement and kappa values were found to be high for patient positioning , bag - mask ventilation , chin lift / jaw thrust , and leak around the facemask among the two assessors , and the options of absence of co2 trace , and difficulty in bag - mask ventilation exhibited 100% agreement .
the average kappa value for inter - rater reliability for the first assessment session was 0.91 and for the second assessment 0.99 , with an average agreement of 95% [ table 2 ] .
inter - rater reliability of the tool for assessment of bag - mask ventilation and tracheal intubation ( percentage agreement and kappa values ) kappa values and percent agreement for test - retest reliability are presented in table 3 .
the average agreement for test - retest reliability was 82% with a kappa value of 0.39 .
determination of construct validity [ table 4 ] showed that senior trainees obtained higher scores compared to the junior trainees in all areas of assessment .
this difference was statistically significant for the sums of scores for patient positioning , preoxygenation , and laryngoscopy technique .
test - retest reliability of the tool for assessment of bag - mask ventilation and tracheal intubation ( percentage agreement and kappa values ) construct validity of the assessment tool for bag - mask ventilation and tracheal intubation
assessment of competence in cognitive knowledge , judgment , communication , including history taking , physical examination , etc . , is routinely done by written , oral , and objective structured clinical examinations .
however , procedural skills have historically been assessed with subjective evaluations done by senior colleagues and supervisors without well - defined criteria or through procedure logs maintained by trainees .
work has been done on defining a minimum number of procedures required to attain competency in anesthetic procedures .
however the relationship between experience , as judged by number of procedures performed , and competence is difficult to define and differs markedly in trainees .
end - of - rotation global rating forms are often filled out by supervising faculty members who have not directly observed trainees performing the procedure on patients .
this form of assessment can not reliably assess procedural skills in their entirety and can not be justified for use in decisions about allowing trainees to perform procedures without direct supervision .
direct observation of the trainee , while performing a procedure on an actual patient , is recommended for a more reliable assessment of competence in procedural skills to enhance the quality of clinical training and ensure patient safety . the construction of procedure - specific assessment tools is therefore required for all complex procedural skills .
it is essential to ensure that the trainee masters the principal components of airway management before he / she is allowed to perform this procedure without direct supervision .
the tool employed in this study was designed specifically for novices in anesthesia and hence the technique was broken down into each of its basic steps forming a checklist with a simple rating scale of 1 - 3 so that the procedure could be assessed in its entirety as recommended for assessment of procedural skills .
the inter - rater reliability for the tool was high . during their training , the anesthesia trainees work at multiple sites with multiple consultants who are responsible for their assessment and provision of feedback .
good inter - rater reliability is , therefore , a basic requirement for this assessment tool .
this would allow the tool to be used by different assessors in different locations depending upon the initial rotations of the trainee .
many other researchers studying the inter - rater reliability of procedure - specific assessment tools for medical trainees have obtained good to excellent results for inter - rater reliability .
the test - retest reliability for the assessment tool does not show as high agreement or kappa values as for inter - rater reliability .
the most probable reason for this seems to be the learning effect involved due to the 3 - 4 weeks interval between the two assessment sessions .
the anesthesia trainees get frequent opportunities to perform bag - mask ventilation and tracheal intubation on a daily basis and thus get the adequate practice to learn and master the skills in the early months of their training .
therefore , their performance might have improved in the 3 - 4 weeks between the two assessments in this study .
we found that the senior trainees obtained higher scores for all steps of bag - mask ventilation and intubation , the difference being significant in many of the steps [ table 4 ] .
this indicates that this procedure - specific structured assessment tool has the ability to discriminate between junior and senior trainees , thus depicting good construct validity .
obtained similar results when testing validity and reliability of an assessment tool for brachial plexus regional anesthesia performance and have recommended their tool for routine use during anesthesia training .
the main use of the tool employed in the current study will be for assessment of junior anesthesia trainees in their first 6 months of training .
bag - mask ventilation and tracheal intubation are among the first few procedural skills that anesthesia trainees learn at the beginning of training and then use it for the rest of their professional career .
the authors hope to use the instrument for formative assessment in novices and for judgment of competence to perform the procedure without direct supervision .
the average assessment score obtained by the group of senior trainees could be used to ascertain the score that the junior trainees must reach before they are trained and assessed for more advanced airway management skills required during difficult intubations and rapid sequence induction . both percent agreement and kappa statistics
were used to analyze the reliability of the tool to increase the strength of the analysis .
the percent agreement does not take account of the possibility that raters may guess on some scores due to uncertainty .
it is therefore advised to calculate both percent agreement and kappa for analysis of inter - rater reliability .
a limitation of our study is that the assessments were done in real time , and , therefore , the assessors were not blinded to the trainees being assessed .
similar studies on assessment tools have been performed by assessing videotaped performance of procedural skills after masking the identity of the trainees or by employing assessors not known to the trainees and vice versa .
efforts were made to reduce this bias by the inclusion of residents who were not rotating with either of the two assessors at the time of assessment .
another limitation of this study is that a relatively long interval was allowed between the two assessment sessions .
this could have affected the value of test - retest reliability due to learning effect , which is the main shortcoming of test - retest reliability studies .
we recommend that the second assessment should be done after shorter intervals to ascertain the test - retest reliability of tools used for assessment of frequently performed procedure such as endotracheal intubation .
the absence of criteria for passing or failing the assessment may be considered as a limitation of the tool .
this has been overcome by adding a sentence : demonstrates ability to perform all aspects of the procedure independently with a yes / no option at the end of the procedural steps .
this section must be carefully filled by the assessors as it identifies whether or not the candidate was able to perform the entire procedure successfully and thus indicates that he / she has passed or not passed in performing the skill .
simulation - based skill assessment is now being described for assessment of residents ' ability to perform anesthetic skills .
however , financial constraints are a limiting factor in developing countries , where reliable and valid assessment tools like ours would be feasible and practical for routine assessment of trainees . as stated by cuschieri et al .
development of objective procedure - specific assessment tools for evaluation of procedural skills and their integration into training programs are the needs of the day . we believe that objective assessment with direct observation using well - defined criteria and rating scales has the potential to greatly improve assessment of procedural skills .
future research should focus on assessing improvement in procedural skills and quality of patient care with implementation of procedure - specific tools for assessment of skills in anesthesia training programs .
our results show that the tool designed by us to assess bag - mask ventilation and tracheal intubation skills in anesthesia trainees demonstrates good construct validity , excellent inter - rater reliability , and fair test - retest reliability . | background and aims : gaining expertise in procedural skills is essential for achieving clinical competence during anesthesia training .
supervisors have the important responsibility of deciding when the trainee can be allowed to perform various procedures without direct supervision while ensuring patient safety .
this requires robust and reliable assessment techniques .
airway management with bag - mask ventilation and tracheal intubation are routinely performed by anesthesia trainees at induction of anesthesia and to save lives during a cardiorespiratory arrest .
the purpose of this study was to evaluate the construct validity , and inter - rater and test - retest reliability of a tool designed to assess competence in bag - mask ventilation followed by tracheal intubation in anesthesia trainees.material and methods : informed consent was obtained from all participants .
tracheal intubation and bag - mask ventilation skills in 10 junior and 10 senior anesthesia trainees were assessed by two investigators on two occasions at a 3 - 4 weeks interval , using a procedure - specific assessment tool.results:average kappa value for inter - rater reliability was 0.91 and 0.99 for the first and second assessments , respectively , with an average agreement of 95% .
the average agreement for test - retest reliability was 82% with a kappa value of 0.39 .
senior trainees obtained higher scores compared to junior trainees in all areas of assessment , with a significant difference for patient positioning , preoxygenation , and laryngoscopy technique , depicting good construct validity.conclusion:the tool designed to assess bag - mask ventilation and tracheal intubation skills in anesthesia trainees demonstrated excellent inter - rater reliability , fair test - retest reliability , and good construct validity .
the authors recommend its use for formative and summative assessment of junior anesthesia trainees . | Introduction
Material and Methods
Data analysis
Results
Discussion
Conclusion
Financial support and sponsorship
Conflicts of interest |
materials rna oligonucleotides described in this work were
obtained from dharmacon and dna oligonucleotides were obtained from
invitrogen .
we cloned ns3 + and ns3 - 4a+-expressing
cdna from the hepatitis c viral genotype 1a ( version h77 , kindly donated by
dr .
the dna oligonucleotides
used for pcr of ns3 and ns3 - 4a were ns3 1a-1 and ns3 1a-2 or ns4a(1a)
bamhi .
an internal xhoi site in the ns3(1a)+ gene was removed through
a silent base pair change using a quikchange kit ( stratagene ) .
the dna
oligonucleotides used for the quikchange reaction were ns3 1a-3 and ns3
1a-4 .
the ns3 + and ns3/4a+ genes from hepatitis c viral
genotype 1b ( version n , kindly provided by dr .
stan lemon
( 24 ) ) were amplified and
cloned into pet15b according to the methods of beran et al .
the upstream dna
oligonucleotide used for pcr amplification was ns3 xhoi and the
downstream dna oligonucleotide was ns3 bamhi or ns4a. ns3 + and ns34a+ of both the 1a and 1b genotypes
were cloned into pet - sumo ( invitrogen ) using extaq pcr ( takara )
followed by ligation with linear pet - sumo according to the
manufacturer 's protocol .
the dna oligonucleotides used were the same as those
described above for pet15b cloning , except that the 5 pcr
oligonucleotide in the genotype 1a case was ns3(1a ) sumo start and in the
genotype 1b case was ns3(1b ) 5 sumo start . to produce pet - sumo - ns4a(1a)+ , the ns4a(1a)+ gene was pcr
amplified using the dna oligonucleotides ns4a 1a sumo start and ns4a 1a sumo
end and then cloned into pet - sumo . to produce the isolated ns3 protease
domain , a stop codon
was inserted in the ns3(1a)+ gene after amino
acid 188 in the pet - sumo - ns3(1a)+ plasmid
( 13 ) .
mutagenesis was
conducted via quikchange ( stratagene ) , using dna oligonucleotides
ns3prot(1a)-1 and ns3prot(1a)-2 . to create the ns3/4a polyprotein with an
ala
/ ala cleavage site instead of a thr / ser cleavage site , the wild - type
ns34a(1b)+ construct was mutated by quikchange ( stratagene ) ,
using oligonucleotides aa ns34a-1 and aa ns34a-2 .
all constructs
were verified initially through pcr screening as necessary and subsequently
sequenced for accuracy ( keck facility , yale university ) .
because there are a multitude of
reports describing the purification of various autocleaved and reconstituted
forms of the ns3 - 4a complex
( 17 ,
22 ,
23 ,
26 ,
27 ) and because all of these
factors greatly influence ns3 enzymatic function
( 13 ) , we believe it is
necessary to describe our constructs , purification strategies , and
reconstitutions in detail .
all proteins were purified according to the methods
described in beran et al . ,
( 13 ,
25 ) .
briefly , 4 liters of
escherichia coli culture in lb ( supplemented with 35 g / ml
kanamycin ) were grown at 37 c with shaking . upon reaching the exponential
growth phase ,
the temperature was shifted to 15 c , the cultures were
supplemented with 1 mm isopropyl
1-thio--d - galactopyranoside ( final concentration ) , and
subsequently incubated overnight at 15 c with shaking .
after lysing the
cells using an emusiflex c5 cell disruptor ( avestin ) , the cellular extract was
centrifuged at 10,000 rpm ( 14,500 g ) at 4 c for 10 min
before being passed through a nickel column .
the his6 and
his6-sumo fusion proteins were purified through a nickel column
( qiagen ) , treated with 10 units of sumo protease ( invitrogen ) overnight at 4
c , and subsequently passed through a gel filtration column ( hiload
superdex 200 16/60 ) equilibrated with a buffer containing 25 mm
hepes ( ph 8.0 ) , 0.3 m nacl , 10% glycerol , 1 mm
dithiothreitol , and 0.2% triton x-100 .
ninety - six 1.2-ml gel filtration
fractions were collected at a rate of 0.4 ml / min .
the ns3 - 4a complex eluted between fractions 45 and 55 , presumably in a
detergent micelle ( 17 ) .
fractions containing ns3 - 4a were identified using the ret - s1 protease assay
( the ret - s1 protease assay details are described later in this section ) as
well as through sds - page analysis . moreover , anti - ns3 and anti - ns4a
( monoclonal antibodies in both cases ) western blotting were used to confirm
the identity of the purified protein complex , which was then used for
experimentation ( see fig .
2 , b and
c , and the western blotting procedure described later in
this section ) .
free ns3 protein eluted from the gel filtration column between fractions 60
and 70 .
fractions containing ns3 were identified using rna unwinding assays
( 25 ) and sds - page analysis . in
addition
, anti - ns3 western blotting was used to confirm the identity of the
purified protein , which was then used for experimentation ( see
fig . 2b and
the
western blotting procedure described later in this section ) . because there is a 13-kda size difference between his - sumo tagged and
untagged protein ,
the untagged proteins were initially analyzed side by side
using sds - page with uncleaved his - sumo ns34a or uncleaved his - sumo - ns3
to verify that the purified proteins were , in fact , untagged species ( data not
shown ) . after purification , preparations were divided into 10-l aliquots and
stored at -80 c .
the ns3 and ns3 - 4a proteins were examined for purity and
their sizes compared using sds - page ( fig .
protein samples ( 40 pmol ) were subjected to
electrophoresis on a nupage 412% bistris gel ( invitrogen ) in mes - sds
buffer for 2 h at 200 v. the gel was subsequently stained with coomassie
blue .
for reconstitution of the protease complex using purified ns3 and purified
ns4a proteins ( ns3 + ns4a ) , we expressed his - sumo - ns3 as well as
his - sumo - ns4a in e. coli using the pet - sumo vector system
( invitrogen ) .
after partial purification using a nickel column , his - sumo - ns3
and a 4-fold excess of his - sumo - ns4a were mixed and incubated together at 4
c overnight in the presence of 10 units of sumo protease ( invitrogen ) .
reconstituted , untagged ns3 + 4a was subsequently isolated from untagged ns3
and untagged ns4a ( based upon size differences ) by passing the protein mixture
through a gel filtration column ( hiload superdex 200 16/60 ) using the same
methods as described above for autocleaved ns3 - 4a .
the same procedure was
followed to reconstitute and purify untagged ns3 protease domain with untagged
ns4a ( ns3 protease domain + ns4a ) . in this case ,
ns3 protease
domain alone eluted between gel filtration fractions 75 and 80 and ns3
protease domain + ns4a eluted between fractions 70 and 75 .
the ret - s1 serine
protease assay as well as sds - page analysis was used to identify the fractions
containing reconstituted ns3 protease domain + ns4a . in all cases ,
sds - page was performed using a bio - rad
miniprotean ii apparatus according to the manufacturer 's protocols .
the
western blot transfer was performed using a bio - rad transfer apparatus
according to the manufacturer 's instructions .
anti - ns3 and anti - ns4a
monoclonal antibodies were purchased from virogen ( watertown , ma ) and diluted
according to the manufacturer 's instructions . in these experiments ( as shown
in fig .
2 , b and
c ) , 25 pmol of each protein was subjected to
electrophoresis on a 12% sds - polyacrylamide gel for 1 h at 200 v.
subsequently , the proteins were transferred to a nitrocellulose membrane by
applying 100 v for 1 h at 4 c .
finally , the blots were incubated with
either anti - ns3 or anti - ns4a monoclonal antibody and subsequently developed
using a pierce supersignal western blot analysis kit .
protease assays protease assays were performed at 37 c
using the resonance energy transfer - s1 substrate ( ret - s1 ) ( anaspec ) designed
by taliani et al .
ret - s1 is an ns4a / ns4b junction mimic that fluoresces upon cleavage . all
assays , unless otherwise indicated , were performed in 60-l reaction
volumes containing 40 nm ns3 - 4a and 5 m ret - s1 .
the
data shown in fig . 6 and
table 1 were collected using
120 nm protein with the indicated amounts of ret - s1 substrate . in
table 1 , the
kcat values were calculated based upon the observation
that 75% of the protein was active in each case
( fig . 5 ) .
the buffer conditions
were the same as those normally used for helicase assays
( 13 ) : 25 mm
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\begin{equation*}{\mathrm{mops - nh}}_{4}^{+}\end{equation*}\end{document } ( ph 6.5 ) , 3 mm
mgcl2 , 1% glycerol , 2 mm dithiothreitol , 30
mm nacl , 0.2% ( v / v )
data
were collected using a cary eclipse spectrophotometer ( varian ) with a
temperature - controlled cuvette holder .
the initial background value ( the
value at time 0 , just before substrate addition ) was subtracted from all
subsequent time points .
table 1the ns3 helicase domain enhances ns3 - 4a protease activity the
proteolysis data were determined by monitoring ret - s1 cleavage on a
fluorescence spectrophotometer ( see experimental procedures ) .
the data shown were determined using proteins of the 1a genotype and is the
average of three experiments . the error values represent standard
deviation.proteinkmvmaxkcatkcat/km mpmol ret - s1 cleaved / spmol ret - s1 cleaved / s / pmol enzymepmol ret - s1 cleaved / s / pmol enzyme/m substrate ns3/4a
10.0 3.0
17 2
3.15 0.30
0.315
ns3 + ns4a
3.0 1.0
0.50 0.05
0.09 0.01
0.030
ns3 protease domain + ns4a
4.0 1.2
0.11 0.01
0.020 0.002
0.005
the ns3 helicase domain enhances ns3 - 4a protease activity the
proteolysis data were determined by monitoring ret - s1 cleavage on a
fluorescence spectrophotometer ( see experimental procedures ) .
the data shown were determined using proteins of the 1a genotype and is the
average of three experiments . the error values represent standard
deviation . the fraction of active ns3 - 4a protein was determined for both tagged and
untagged preparations by incubating a small amount of enzyme ( 40
nm ) with a large amount of ret - s1 substrate ( 5 m ) .
a
line was fit to the slope of the proteolysis data during the steady - state
phase of reaction .
this line was extrapolated to the intersection with the
y axis ( sigma plot , systat software ) , which corresponds to the
concentration of active enzyme present in the reaction
( 28 ) . in all cases throughout
this work ,
importantly ,
similar values for the fraction of active enzyme ( 75% ) were observed when
the ns3 - 4a concentration was raised to 120 nm or when the ret - s1
concentration was raised well above the km ( 10 3
m ) ( table 1 ) to
20 m ( data not shown ) . similarly , when reconstituted ns3
protease domain + ns4a and ns3 + ns4a were assayed with ret - s1 concentrations
well above the km values ( 810 m
ret - s1 , whereas km = 4.0 1.2 and 3.01.0
m , respectively ) ( table
1 ) , a similar enzymatic active fraction was observed for both
complexes ( 75% ) ( data not shown ) . when protease activities of ns3 - 4a(1a )
and ns3 - 4a(1b ) were compared using the ret - s1 analyses , results were similar
for both genotypes
the ns3 - 4a complex can be purified in a highly active
form to study ns3 - 4a protease function , we needed to purify ns3 in
complex with its ns4a co - factor ( i.e. ns3 - 4a ) . in previous studies
,
ns3 - 4a has been overexpressed in insect cells
( 27 ) or in e. coli
( 12 ,
17 ) . in all of these cases ,
additional amino acids were fused to the ns3 n terminus for the purpose of
protein purification ( 12 ,
17 ) and lysine residues were
added to the ns4a c terminus to increase solubility
( 17 ) . to our knowledge , a
recombinant ns3 - 4a complex that lacks tags or additional modifying amino acids
has never been produced .
we therefore designed an approach for generating
native , full - length ns3 - 4a complex ( e.g. lacking modifications to the
terminal sequences of ns3 or ns4a ) using the pet - sumo expression system in
e. coli ( fig .
the protein of interest is tagged at the n terminus with the sumo
polypeptide , which enhances solubility of the protein and is then readily
removed upon incubation with the sumo protease , thereby resulting in native
protein that lacks additional amino acids
( 29 ) .
we expressed ns3 - 4a as a his - sumo - ns3/4a polyprotein in e. coli ,
designing the construct so that ns3 would be expected to spontaneously cleave
ns4a from its c terminus ( fig .
1b ) ( 17 ,
27 ) , thereby forming an active
protease complex ( 4 ) .
after
purification on a nickel column , the his - sumo fusion protein was cleaved by
sumo protease from ns3 , generating a native n terminus
( fig .
the protein
mixture was subsequently passed through a gel filtration column to separate
native protein complex from uncleaved fusion protein ( see experimental
procedures ) .
the resultant cleaved , purified ns3 - 4a complex was
95% pure ( fig .
2a ) . to determine whether the purified ns3 - 4a protein had autocatalytically
cleaved properly , forming two separate proteins ( ns3 and ns4a ) , we subjected
the complex to denaturing electrophoresis side by side with ns3 and an
uncleavable ns3/4a polyprotein control .
the uncleavable ns3/4a polyprotein was
produced by mutating the conserved junction amino acid sequence between ns3
and ns4a from thr / ser to ala / ala .
sds - page and western blot analysis show that
the ns3 component of the wild - type ns3 - 4a preparation has the same
electrophoretic mobility as ns3 ( in fig .
2a , compare lanes 2 and 3 of the
coomassie - stained gel and in fig .
2b , compare lanes 1 and 2 of the
anti - ns3 western blot ) .
however , the uncleaved ns3/4a polyprotein migrates
more slowly than ns3 , as expected due to its larger size ( in
fig .
2a , compare
lane 4 to lanes 2 and 3 and in
fig .
coomassie staining does
not reveal any ns3/4a polyprotein in our ns3 - 4a preparation
( fig . 2a , lane
3 ) . however , western blots are more sensitive than coomassie staining ,
and consistent with this , the anti - ns3 western blots reveal a small fraction
of uncleaved ns3/4a polyprotein in the wild - type ns34a preparation
( fig . 2b , note the
faint upper band in lane 2 that migrates similarly to the ns3/4a
polyprotein in lane 3 ) . taken together , these results demonstrate
that the preparation of wild - type ns3 - 4a complex is composed primarily of
fully cleaved ns3 and ns4a molecules . the catalytic function and
conformational homogeneity of this preparation
figure 1.composition and purification of ns3 - 4a . the ns3 - 4a complex
organization and
a , pro refers to the serine protease domain
and the roman numerals indicate the respective ns3 helicase
subdomains .
the regions where atp , rna , and the ns4a co - factor bind are
indicated as well .
the protein construct expressed in e. coli is
depicted in panel b. the numbers below the map refer to the
hcv polyprotein numbering of the amino acids of ns3 - 4a . in panel c ,
his - sumo - ns3 and his - sumo - ns4a fusion construct designs are presented .
these
proteins were purified separately and their his - sumo tags were removed using
the same methods as for ns3 - 4a .
subsequently , the native ns3 or native ns3
protease domain was reconstituted with native ns4a ( see experimental
procedures ) .
the ns3 - 4a complex
organization and construct design are illustrated schematically ( a
and b ) . in panel
a , pro refers to the serine protease domain
and the roman numerals indicate the respective ns3 helicase
subdomains . the regions where atp , rna , and the ns4a co - factor bind are
indicated as well .
the protein construct expressed in e. coli is
depicted in panel b. the numbers below the map refer to the
hcv polyprotein numbering of the amino acids of ns3 - 4a . in panel c ,
his - sumo - ns3 and his - sumo - ns4a fusion construct designs are presented .
these
proteins were purified separately and their his - sumo tags were removed using
the same methods as for ns3 - 4a .
subsequently , the native ns3 or native ns3
protease domain was reconstituted with native ns4a ( see experimental
procedures ) .
the presence of ns4a in the ns3 - 4a preparation was assessed using
denaturing electrophoresis and western blot analysis with antibodies against
ns4a .
the anti - ns4a western blots indicate that the wild - type ns3 - 4a
preparation consists of both free ns4a ( which is difficult to detect because
it is so small and diffuses rapidly from the gel ) and a fraction of uncleaved
ns3/4a polyprotein ( in fig .
the free
ns4a migrates at the correct position , 6 kda , near the bottom of the gel
( fig .
2c , lane
2 ) . taken together , the electrophoretic and immunoaffinity methods
provide physical evidence that the ns3 - 4a preparation consists of cleaved ns3
and ns4a components . nonetheless , it was still essential to demonstrate that
the complex was catalytically active and to assess the fraction of active
molecules in the preparation .
a , purified
proteins were subjected to denaturing electrophoresis on a 412%
gradient gel .
purified ns3 ( lane 2 ) , ns3 - 4a ( lane 3 ) , and
ns3/4a polyprotein ( lane 4 ) were subjected to electrophoresis side by
side for comparison of mobilities .
the band shown in lane 3
represents the ns3 component of a native , fully cleaved ns3 - 4a preparation .
the band shown in lane 4 represents an ns3/4a polyprotein preparation
produced by mutating the thr / ser cleavage site between ns3 and ns4a to a
non - cleavable sequence ( aa ) . in panels b and c ,
anti - ns3 and
anti - ns4a western blot analysis confirm the identity of our purified proteins
( see experimental procedures ) .
b , lane 1 contains purified ns3 ,
lane 2 contains purified , full - length ns3 - 4a , and lane 3
contains purified ns3/4a polyprotein .
truncated forms of ns3 are visible below
the full - length protein in each lane in the anti - ns3 blot .
these truncated
forms of ns3 are likely produced during bacterial expression as well as during
the multiday purification performed in the absence of protease inhibitors .
these truncated forms could represent either n- or c - terminal truncations of
ns3 as the monoclonal anti - ns3 antibody binds to the central region of the
helicase domain .
lane 1 contains purified ns3 , lane 2 contains
purified , full - length ns3 - 4a , and lane 3 contains purified ns3/4a
polyprotein .
truncated forms of the ns3/4a polyprotein are visible
below the full - length polyprotein in the anti - ns4a blot .
these
truncated forms of ns3/4a polyprotein likely represent n - terminal degraded
ns3/4a as the monoclonal anti - ns4a antibody binds the final 11 c - terminal
residues of ns4a .
a , purified
proteins were subjected to denaturing electrophoresis on a 412%
gradient gel .
purified ns3 ( lane 2 ) , ns3 - 4a ( lane 3 ) , and
ns3/4a polyprotein ( lane 4 ) were subjected to electrophoresis side by
side for comparison of mobilities .
the band shown in lane 3
represents the ns3 component of a native , fully cleaved ns3 - 4a preparation .
the band shown in lane 4 represents an ns3/4a polyprotein preparation
produced by mutating the thr / ser cleavage site between ns3 and ns4a to a
non - cleavable sequence ( aa ) . in panels
b and c , anti - ns3 and
anti - ns4a western blot analysis confirm the identity of our purified proteins
( see experimental procedures ) .
b , lane 1 contains purified ns3 ,
lane 2 contains purified , full - length ns3 - 4a , and lane 3
contains purified ns3/4a polyprotein .
truncated forms of ns3 are visible below
the full - length protein in each lane in the anti - ns3 blot .
these truncated
forms of ns3 are likely produced during bacterial expression as well as during
the multiday purification performed in the absence of protease inhibitors .
these truncated forms could represent either n- or c - terminal truncations of
ns3 as the monoclonal anti - ns3 antibody binds to the central region of the
helicase domain .
lane 1 contains purified ns3 , lane 2 contains
purified , full - length ns3 - 4a , and lane 3 contains purified ns3/4a
polyprotein .
truncated forms of the ns3/4a polyprotein are visible
below the full - length polyprotein in the anti - ns4a blot .
these
truncated forms of ns3/4a polyprotein likely represent n - terminal degraded
ns3/4a as the monoclonal anti - ns4a antibody binds the final 11 c - terminal
residues of ns4a . to quantify the fraction of fully processed , active ns3 - 4a in the
preparation , we analyzed the proteolysis of a depsipeptide substrate known as
ret - s1 , which was originally derived from the ns4a
both free ns3
and the uncleavable mutant ns3/4a polyprotein are proteolytically inactive , as
they fail to react with ret - s1 ( see below ) .
however , the wild - type ns3 - 4a
preparation displays efficient protease activity against ret - s1 , with a rate
constant of 0.020 0.001 m product / s ) .
this value is
significantly faster than values obtained by others for ns3 - 4a with a
non - native n terminus incubated with a 5ab peptide substrate
( 27 ) . importantly ,
burst
kinetics experiments reveal that the ns3 - 4a preparation contains 75
14% active enzyme ( fig .
3 ) ,
indicating that the majority of the population is properly folded , assembled ,
and catalytically active .
that this value falls short of 100% is consistent
with the electrophoretic analyses , which indicated that 20% of the
wild - type ns3 - 4a preparation remains uncleaved
( fig .
the
physical and functional information provided by both the electrophoretic and
proteolysis assays indicate that we have successfully overexpressed untagged ,
unmodified ns3 - 4a in a form that is conformationally homogeneous ,
appropriately cleaved , and highly reactive .
this approach now makes it
possible to quantitatively assess the proteolysis and helicase activities of
the ns3 - 4a complex , and to compare these activities with the behavior of other
ns3 constructs .
figure 3.steady-state proteolysis of ret - s1 by ns3 - 4a and his - ns3 - 4a .
the
y intercept of the line in each case corresponds to the active
fraction of protein ( see experimental procedures ) . for ns3 - 4a
( solid circles ) ,
for
his - ns3 - 4a ( hatched squares ) , the active fraction was 25
12% .
ns3/4a polyprotein did not display any measurable serine protease
activity ( solid squares ) .
similar results were observed using ns3 - 4a(1a )
and his - ns3 - 4a(1a ) .
this data are the average of three experiments and the
error values represent standard deviation .
steady - state proteolysis of ret - s1 by ns3 - 4a and his - ns3 - 4a .
the
y intercept of the line in each case corresponds to the active
fraction of protein ( see experimental procedures ) . for ns3 - 4a
( solid circles ) , the active fraction was 75 14% . for
his - ns3 - 4a ( hatched squares ) ,
ns3/4a polyprotein did not display any measurable serine protease
activity ( solid squares ) .
similar results were observed using ns3 - 4a(1a )
and his - ns3 - 4a(1a ) .
this data are the average of three experiments and the
error values represent standard deviation .
most previous work on ns3 has utilized n - terminal his - tagged variants of
the protein ( 12 ,
13 ,
30 ,
31 ) . for comparison purposes
,
we also constructed an ns3 - 4a complex with a his tag on the n terminus of ns3 .
interestingly , kinetic analysis indicates that the his - tagged ns3 - 4a
preparation reacts 2-fold more slowly than the untagged variant ( 0.010
0.001 m product / s ) , and contains only a 25
12% active population ( fig . 3
and experimental procedures ) .
a his tag at the ns3 n terminus is
therefore detrimental for folding and/or assembly of the protease domain , and
it also diminishes the ultimate levels of proteolytic activity by the tagged
ns3 - 4a complex .
these findings are consistent with the fact that n - terminal
ns3 his tags are in close proximity to the protease active site .
uncleaved ns3/4a polyprotein lacks protease and helicase
activities the uncleavable ns3/4a polyprotein construct ( containing
2 alanines where the threonine / serine cleavage sequence n - terminal to ns4a
would have been ) was synthesized originally as a tool that would provide a
size standard for determining the presence of any uncleaved ns3/4a polyprotein
in wild - type preparations of the complex .
however , the mutant ns3/4a construct
has also provided valuable additional information about the activities that we
should expect for hcv polyproteins . to our knowledge , catalytic activities of
uncleaved ns3/4a constructs have never been tested .
here we observed , using
the mutant polyprotein , that uncleaved ns3/4a molecules are catalytically
inactive ( i.e. they lack both serine protease and helicase activity ) .
they fail to display protease activity for substrates provided in
trans ( i.e. ret - s1 ) ( fig .
thus , proper
assembly of the cleaved , ns3 - 4a complex is required for all the enzymatic
activities of this protein .
it is therefore likely that many sections of the
polyprotein are not appropriately folded or functional until the individual
proteins are cleaved apart .
figure 4.steady-state velocity curves for ns3 - 4a proteolysis of ret - s1 under a
range of ph and salt conditions .
the steady - state rates of proteolysis
were 0.006 0.001 m product / s at ph 6.5 , 30
mm nacl ( solid circles ) , 0.019
0.001m product / s at ph 8 , 30 mm nacl ( pierced
circles ) , 0.019 0.001 m product / s at ph 6.5 , 75
mm nacl ( solid diamonds ) , 0.020 0.001
m product / s at ph 8 , 75 mm nacl ( pierced
diamonds ) , 0.010 0.001 m product / second at ph
6.5 , 200 mm nacl ( solid squares ) , and 0.010 0.001
m product / s at ph 8 , 200 mm nacl ( pierced
squares ) .
the active fraction in each case , as determined by intersection
with the y intercept , was 68 9% for ph 6.5 , 30 mm
nacl , 84 16% for ph 8.0 , 30 mm nacl , 84 15% for
ph 6.5 , 75 mm nacl , 70 12% for ph 8.0 , 75 mm
nacl , 95 5% for ph 6.5 , 200 mm nacl , and 95 5%
for ph 8.0 , 200 mm nacl .
the data shown were determined using
ns3 - 4a of the 1b genotype and represent the steady - state data points fit to a
line .
this data are the
average of three experiments and the error values represent standard
deviation .
steady - state velocity curves for ns3 - 4a proteolysis of ret - s1 under a
range of ph and salt conditions .
the steady - state rates of proteolysis
were 0.006 0.001 m product / s at ph 6.5 , 30
mm nacl ( solid circles ) , 0.019
0.001m product / s at ph 8 , 30 mm nacl ( pierced
circles ) , 0.019 0.001 m product / s at ph 6.5 , 75
mm nacl ( solid diamonds ) , 0.020 0.001
m product / s at ph 8 , 75 mm nacl ( pierced
diamonds ) , 0.010 0.001 m product / second at ph
6.5 , 200 mm nacl ( solid squares ) , and 0.010 0.001
m product / s at ph 8 , 200 mm nacl ( pierced
squares ) . the active fraction in each case , as determined by intersection
with the y intercept , was 68 9% for ph 6.5 , 30 mm
nacl , 84 16% for ph 8.0 , 30 mm nacl , 84 15% for
ph 6.5 , 75 mm nacl , 70 12% for ph 8.0 , 75 mm
nacl , 95 5% for ph 6.5 , 200 mm nacl , and 95 5%
for ph 8.0 , 200 mm nacl .
the data shown were determined using
ns3 - 4a of the 1b genotype and represent the steady - state data points fit to a
line .
this data are the
average of three experiments and the error values represent standard
deviation .
ns3 - 4a exhibits robust serine protease activity under a variety of salt
and ph conditions it has previously been reported that ns3 - 4a only
functions as a robust serine protease under conditions of high salt ( 150
mm nacl ) and high ph ( 7.58.0 )
( 17 ,
27 ) .
these same conditions are
incompatible with those required for ns3 helicase activity
( 13 ,
17 ,
32 ) , and it therefore has been
suggested that the two activities ( proteolysis and unwinding ) might be
mutually exclusive ( 17 ) .
we
therefore sought to determine whether protease activity of the wild - type
ns3 - 4a complex is restricted to the narrow range of previously reported
conditions . to this end , we measured ns3 - 4a serine protease activity under a
variety of ph ( 6.5 and 8.0 ) and salt conditions ( 30 , 75 , and 200 mm
nacl ) ( fig .
4 ) . we did not
observe significant differences in the active fraction of protein
( i.e. the y intercept of the velocity plots ) under these
varying ph and salt conditions , particularly when accounting for error
( fig .
the
steady - state proteolysis velocities in 30 mm nacl at ph 6.5 and 8.0
were observed to be 0.006 0.001 and 0.019 0.001
m / s , respectively . in 200 mm nacl at ph 6.5 and 8.0 ,
the steady - state proteolysis velocities were observed to be 0.010
0.001 m / s in both cases .
therefore , native , full - length ns3 - 4a
is a robust serine protease under a broad range of salt and ph conditions ,
including those that are compatible with helicase activity .
figure 5.steady-state proteolysis of ret - s1 by reconstituted ns3 + ns4a and ns3
protease domain + ns4a .
the steady - state velocity for ns3 + ns4a is 0.005
001 m / s ( pierced circles ) and for ns3
protease ns4a is 0.001 0.001 m / s ( solid
squares ) .
the y intercept of the fitted lines show ns3
+ ns4a and ns3 protease domain + ns4a to have 75 10% active fraction
and 75 12% active fraction , respectively .
the data shown are the
average of three experiments and the error values represent standard
deviation .
steady - state proteolysis of ret - s1 by reconstituted ns3 + ns4a and ns3
protease domain + ns4a .
the steady - state velocity for ns3 + ns4a is 0.005
001 m / s ( pierced circles ) and for ns3
protease ns4a is 0.001 0.001 m / s ( solid
squares ) .
the y intercept of the fitted lines show ns3
+ ns4a and ns3 protease domain + ns4a to have 75 10% active fraction
and 75 12% active fraction , respectively .
the data shown are the
average of three experiments and the error values represent standard
deviation .
ns3hel enhances ns3 - 4a serine protease activity given that
efficient ns3 helicase activity requires the protease domain
( 13 ) , we asked whether ns3
protease activity is enhanced by the helicase domain . to answer this question ,
it was necessary to build new types of protein expression constructs because
polyprotein precursors containing the isolated protease domain ( i.e.
a his - sumo - ns3 protease domain / ns4a polyprotein construct ) did not undergo
autocatalytic cleavage to form an ns3 protease-4a complex ( data not shown ) .
we
therefore expressed the ns3 protease domain and full - length ns4a as separate
his - sumo fusion proteins ( fig .
the partially purified his - sumo - ns3 protease domain and his - sumo - ns4a proteins
were then combined in the presence of sumo protease and incubated to form an
active complex of the native ns3 protease domain and native ns4a ( ns3 protease
+ ns4a , see experimental procedures ) .
similarly , we
reconstituted full - length ns3 + ns4a as a control for comparative purposes
( fig .
similar to the preparation of co - expressed ns3 - 4a , 75 10% of the
reconstituted ns3 + ns4a preparation and 75 12% of the reconstituted
ns3 protease + ns4a preparations were proteolytically active
( fig .
comparison of the
kinetic parameters for ns3 - 4a , ns3 protease domain + ns4a , and ns3 + ns4a
proteolysis of ret - s1 revealed that the km values for
cleavage of substrate did not differ significantly ( km =
10.0 3.0 m for ns3 - 4a , 4.0 1.2
m for ns3 protease + ns4a , and 3.0 1.0
m for ns3 + ns4a ) ( fig .
6 and table 1 ) ,
indicating that ret - s1 binds similarly to all the constructs .
figure 6.steady-state proteolysis rates of ret - s1 by ns3 - 4a , ns3 + ns4a , and ns3
protease domain + ns4a in the presence of varying substrate
concentrations .
the data were fit to the michaelis - menten equation to
determine km , vmax , and
kcat values .
steady - state proteolysis rates of ret - s1 by ns3 - 4a , ns3 + ns4a , and ns3
protease domain + ns4a in the presence of varying substrate
concentrations .
the data were fit to the michaelis - menten equation to
determine km , vmax , and
kcat values .
however , the maximal velocities of proteolysis by the three enzyme
constructs were substantially different .
the rates of cleavage for ns3 - 4a , ns3
+ 4a , and ns3 protease + 4a were 17.0 2.0 , 0.50 0.05 , and
0.11 0.01 pmol of ret - s1 cleaved / s , respectively
( fig .
the large rate
differences between the co - expressed ns3 - 4a and the reconstituted ns3 + ns4a
constructs suggest that the ns4a cofactor does not associate and promote
protease folding as effectively when presented in trans
( i.e. 25 mm hepes ( ph 8.0 ) , 0.3 m nacl , 10%
glycerol , 1 mm dithiothreitol , 0.2% triton x-100 ) .
many conditions were explored to optimize reconstitution with ns4a in
trans . despite varying detergent concentrations ( 0.11% , using
triton x-100 or chaps ) ,
varying glycerol concentrations from 10 to 50% , and
varying nacl from 30 to 200 mm , increases in proteolytic activity
were not observed ( data not shown ) . taken together ,
these data suggest that the protease domain active site is
optimally formed only upon co - expression with ns4a .
nonetheless , the
reconstituted complexes retain significant levels of activity and provide
valuable tools for structure / function studies
( 5 ,
22 ) . given the inherently higher reactivity of co - expressed ns3 - 4a , it is clear
that proteolytic activity of the isolated protease domain ( ns3 protease + 4a )
is directly comparable only with the reconstituted complex containing
full - length ns3 ( ns3 + 4a ) . when these two constructs are compared , the
isolated protease domain is much less reactive than full - length ns3
( fig .
indeed , ns3
protease + ns4a is 5- and 6-fold less efficient than ns3 + ns4a when
vmax and kcat / km
values are compared , respectively ( table
1 ) .
it is notable that the major effects are on
kcat , which suggests that the helicase domain directly
influences catalytic function of the protease active site .
therefore , ns3
protease activity is enhanced by the presence of the ns3hel domain , indicating
that the two domains have evolved to become completely interdependent .
by creating new types of ns3 constructs and monitoring their enzymatic
activities , we have evaluated the structural integrity and catalytic potential
of the serine protease domain .
we have established that ns3 protease activity
is strongly influenced by its structural context , and that positive and
negative effects on catalysis are induced by the presence of adjacent domains
and uncleaved polyprotein moieties , respectively . taken together
, our findings
suggest that ns3 protease activity is tuned and regulated by other viral
components , which have coevolved to maximize the role of the protease in the
hcv viral lifecycle .
the helicase and the protease are interdependent enzymes within a
single protein like many viral proteins , ns3 is multifunctional and
it contains different enzymatic activities within a single protein chain .
it
has long been known that the protease and atpase / helicase activities of ns3
are located on separate domains of ns3 , and given the disparate nature of
these activities , and their presumably different roles in function of the
virus , it was generally assumed that the protease and helicase activities had
no relationship to one another .
however , structural analysis revealed that the
protease domain is located in close proximity to the atpase and rna binding
sites of ns3hel ( 33 ,
34 ) .
we therefore wondered
whether the two enzymes in ns3 might actually be interdependent , having
evolved to function optimally as a unit .
allosteric coactivation would have
important ramifications for the function of the hcv replication complex and
for the testing of hcv inhibitors , which tends to be studied with the isolated
domains . in our first study of this problem
, we showed that rna binding , atpase , and
rna unwinding activities of the helicase are all stimulated by the presence of
the covalently attached ns3 protease domain
( 13 ) . here
we demonstrate that
the ns3 - 4a serine protease activity is stimulated by the presence of ns3hel as
well .
importantly , the ns3hel domain must be covalently attached to the ns3
protease domain , as adding ns3hel in trans had no effect on ns3
protease domain + ns4a protease activity ( data not shown ) .
thus , the different
enzymatic domains of ns3 are fully interdependent , which suggests that they
have coevolved and that their presence on a single protein may have provided a
selective advantage to the virus .
perhaps most importantly , the results
suggest that these seemingly disparate enzymatic activities may somehow be
coupled during some aspect of viral function .
the ns3/4a polyprotein fails to catalyze proteolysis or
unwinding just as the helicase domain activates serine protease
activity , the presence of an uncleaved ns3/4a junction inhibits serine
protease activity .
the data presented herein show that polyprotein cleavage
must occur before ns3 becomes proteolytically active .
even ns3 helicase
activity requires cleavage of the ns3/4a junction sequence before any rna
unwinding activity is observed ( data not shown ) .
taken together , these data
indicate that polyprotein processing must necessarily be a very early event ,
as it is required for catalytic functions of viral constituents .
proteolysis and helicase activities are not mutually
exclusive previous work has suggested that ns3 - 4a protease activity
occurs under conditions that are incompatible with helicase activity .
this
finding implies that helicase and protease activities might be mutually
exclusive , or that their viral functions are completely unrelated .
importantly , it had been reported that ns3 - 4a protease activity is very
sensitive to salt concentrations when the protein is studied at low
concentrations ( < 1 nm ) and less sensitive to salt concentrations
at higher protein concentrations ( 1 nm )
( 22 ) .
we therefore conducted
protease assays with relatively high ns3 - 4a concentrations ( 40120 nm )
that fall within the range typically employed for rna helicase assays
( 12 ,
13 ,
25 ,
31 ) .
our ability to observe
helicase and protease activity under the same conditions may also stem from
the fact that we utilized untagged ns3 - 4a , which is more reactive than
his - tagged ns3 - 4a .
an n - terminal his tag reduces both the rate of serine
protease activity and the active fraction of protein
( fig .
proteolysis
by untagged ns3 - 4a is not highly salt dependent and the reaction is efficient
under diverse conditions ( fig .
4 ) .
earlier work has demonstrated that ns3 functions as a robust rna helicase
at nacl concentrations as high as 100 mm and it can unwind rna at
even higher nacl concentrations , although less efficiently
( 13 ) . the fact that ns3 can
cleave protein or unwind rna in the same range of salt and ph conditions
( including ionic conditions that approach physiological ( 150 mm ) )
indicates that ns3 - 4a is capable of transitioning smoothly between proteolysis
and rna unwinding during various stages of hcv replication . immediately after
ns3 - 4a autocleaves from the hcv polyprotein
, it may unwind hcv rna or use
ns3hel as a motor to translocate along the hcv polyprotein and scan for
subsequent peptide cleavage sites .
protein translocation by ns3hel has never
been demonstrated , but its potential importance is underscored by the
translocase activities of related proteins such as clpx
( 3537 ) . reconstituted forms of ns3 - 4a are significantly less reactive than
autocleaved ns3 - 4a to perform this study , it was necessary to
create reconstituted forms of the ns3 - 4a complex , in which the 4a protein was
added in trans to the serine protease domain or to the full - length
ns3 .
this provided an opportunity to compare the reactivities of ns3 - 4a
molecules that , despite identical sequences , were produced in different ways
( through autocleavage of polyprotein or reconstitution from separate
proteins ) . here
we observe that autoproteolyzed ns3 - 4a is a much more active
serine protease than complexes that were reconstituted from separate ns4a
molecules ( ns3 + ns4a ) .
consistent with this , the ns3 - 4a complex that is
disrupted by dilution into low salt buffers
( 17 ) can not be restored to
normal levels of the protease activity by the addition of salt ( data not
shown ) .
specifically , we observe that ns3 - 4a has a vmax
for ret - s1 proteolysis that is 34 times faster than ns3 + ns4a
( table 1 ) .
intriguingly , the
km values for ns3 - 4a and ns3 + ns4a proteolysis of ret - s1
do not vary significantly ( table
1 ) . taken together
, the kinetic analysis of proteolysis by ns3 - 4a ,
ns3 + ns4a , and ns3 protease + ns4a suggests that all of these constructs bind
substrate with a similar affinity , but they have large differences in
efficiency of chemical catalysis .
one possible explanation is that the ns4a co - factor may not properly
intercalate with the ns3 protease domain when ns3 and ns4a are simply mixed ,
potentially resulting in misalignment of active site residues within the ns3
protease domain .
autocleavage between ns3 and ns4a and the concurrent
intercalation of ns4a into the ns3 protease domain requires a specific
cleavage site sequence that slows the proteolysis reaction ( thr / ser as opposed
to cys / ser at other hcv polyprotein sites )
( 38 ) .
presumably , this slow
autocleavage between ns3 and ns4a facilitates the correct intercalation of
ns4a into the ns3 protease domain as ns4a is being cleaved from the ns3 c
terminus ( 38 ) .
therefore ,
whereas our findings suggest that the helicase domain allosterically
influences the protease active site , an alternative interpretation of the
results is that a coexpressed helicase domain is required for proper folding
of the protease domain and/or appropriate docking of the 4a cofactor . in
addition
, the expression strategy employed in this work may not optimally
recapitulate folding of the individual proteins . but
regardless of the
mechanistic basis for the apparent codependence of the protease and the
helicase , the data clearly show that reconstituted ns3 and 4a constructs are
significantly impaired , which has major implications for the design of protein
constructs used in drug screening and for structure / function efforts on
hcv .
many investigators have aimed to disrupt ns3 - 4a protease activity as an
approach toward antiviral therapeutics and various forms of the complex have
been employed in these studies
( 1923 ,
39 ) .
although it has been
suggested that ns3hel might enhance ns3 - 4a protease activity
( 23 ) , this synergy was not
demonstrated until now .
our findings suggest that screens for ns3 - 4a protease
inhibitors should involve full - length ns3 constructs rather than truncated
protease domains .
moreover , these screens should utilize constructs in which
ns3 - 4a is produced through autoproteolysis rather than reconstitution .
indeed ,
a recent study comparing the effects of ns3 - 4a serine protease inhibitors on
full - length ns3 - 4a produced through autocleavage , ns3 + ns4a peptide , and ns3
protease domain + ns4a peptide demonstrated that biln 2061 and vx-950 are much
better inhibitors of autocleaved ns3 - 4a serine protease activity than of
reconstituted ns3 + ns4a peptide or ns3 protease domain + ns4a
( 22 ) .
the greater protease
activity of autocleaved ns3 - 4a creates the potential for increased sensitivity
when measuring protease activity in the presence of new drugs ( i.e.
more easily measured inhibition of protease activity in screening assays of
compound libraries ) , which will lead to a greater diversity of promising lead
compounds . given the synergies observed among components of the ns3
helicase - protease , it will be interesting to monitor the influence of ns4a on
rna binding , atpase , and rna unwinding activities of ns3 in future
studies . | non - structural protein 3 ( ns3 ) is a multifunctional enzyme possessing
serine protease , ntpase , and rna unwinding activities that are required for
hepatitis c viral ( hcv ) replication .
hcv non - structural protein 4a ( ns4a )
binds to the n - terminal ns3 protease domain to stimulate ns3 serine protease
activity .
in addition , the ns3 protease domain enhances the rna binding ,
atpase , and rna unwinding activities of the c - terminal ns3 helicase domain
( ns3hel ) . to determine whether ns3hel enhances the ns3 serine protease
activity , we purified truncated and full - length ns3 - 4a complexes and examined
their serine protease activities under a variety of salt and ph conditions .
our results indicate that the helicase domain enhances serine protease
activity , just as the protease domain enhances helicase activity .
thus , the
two enzymatic domains of ns3 - 4a are highly interdependent .
this is the first
time that such a complete interdependence has been demonstrated for a
multifunctional , single chain enzyme .
ns3 - 4a domain interdependence has
important implications for function during the viral lifecycle as well as for
the design of inhibitor screens that target the ns3 - 4a protease . | EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
Supplementary Material |
many efforts have been undertaken to unravel the role of the immune system in the pathogenesis of nonalcoholic steatohepatitis ( nash ) . the balance between proinflammatory th17 and the regulatory t cells ( tregs ) , which plays a major role in the control of inflammation , appears to be disturbed in various diseases , such as autoimmune , infectious , inflammatory , and metabolic diseases .
th17 are a subset of effector t cells that express the nuclear receptor retinoid - related orphan receptor t ( rort ) and produce il17 .
an upregulation of the th17 pathway has been described in the liver in fatty liver disease and in liver fibrosis , which is the hallmark of progressive liver disease .
opposite to these findings , a protective role of il17 was described in obesity , since il17 acted as a negative regulator of adipogenesis and glucose metabolism in mice and delayed the development of obesity .
accordingly , a reduction of th17 in abdominal adipose tissue ( aat ) was described in mice fed a high fat diet ( hfd ) .
tregs derive from cd4 + th0 cells and constitutively express cd25 ( the il2 receptor chain ) .
in addition , they express foxp3 ( forkhead / winged helix transcription factor ) that is crucial for their function . in a hfd mouse model , a liver - specific and reversible depletion of tregs was observed , while human studies showed their increase in liver biopsies of nash patients with a more severe disease .
moreover , tregs were specifically reduced in the aat of preclinical insulin - resistant models of obesity [ 6 , 10 ] , while in obese patients some authors described an increase of foxp3 rna in the subcutaneous adipose tissue ( sat ) and others found a downregulation of foxp3 rna only in obese patients without insulin resistance , while no difference was found when comparing insulin - resistant obese patients and lean controls .
other key factors in the pathogenesis of nash are the adipokines , which are mainly produced in the white adipose tissue .
high to normal serum leptin levels can be found in nash patients independently from the body mass index ( bmi ) .
leptin has also important proinflammatory effects , acting both on the innate and on the adaptive immunity [ 14 , 15 ] .
recent lines of evidence have shown that leptin is implicated in the upregulation of the th17 pathway [ 16 , 17 ] and in the suppression of treg proliferation . in order to further elucidate the differential role of th17 and tregs at different anatomical sites in the pathogenesis of nash , we analyze in the present study the treg and th17 populations in mice fed hfd and their location - specific modifications with particular interest in liver and aat and sat .
moreover we analyze the possible correlation between the tissue - specific variations of these cells and the diet - induced disturbances of metabolic homeostasis .
c57bl6/j six - to - eight - week - old male mice were purchased ( charles river laboratories , brussels , belgium ) and kept at the animal facility of the university of antwerp in temperature- and light - controlled conditions .
mice were fed for 36 weeks with either hfd ( with 60% of kcals derived from fat , 20% from proteins , and 20% from carbohydrate ) ( research diets ) or normal chow , in line with what was previously described .
mice were weighed weekly and just prior to sacrifice . at sacrifice blood samples , sat , epididymal fat tissue and liver were obtained . in mice
epididymal fat is able to influence the major components of the metabolic syndrome , as shown by the improvement of insulin sensitivity and the decrease of leptin secretion by sat after its removal .
the protocols were approved by the antwerp university ethical committee on animal experiments ( permit number : 2012 - 47 ) .
the animals received human care and were treated according to the helsinki declaration , the national guidelines for animal protection , and the guide for the care and use of laboratory animals
blood samples on ethylenediaminetetraacetic acid ( edta ) were collected from anesthetized mice by cardiac puncture . sat and aat and liver were excised after flushing organs through the right ventricle with 5 ml of cold phosphate buffered saline ( pbs ) ( sigma ) and cut into small pieces of 1 - 2 mm .
liver tissue was smashed through a sieve and intrahepatic immune cells were harvested after centrifugation with 33% percoll ( sigma ) and heparin .
fat tissue fragments were incubated for 60 minutes with collagenase type ii ( sigma ) , filtered , and incubated with dnase i ( sigma ) for 20 min .
the cells were incubated with the following fluorochrome conjugated antibodies : cd45-ef450 ( bd ) , cd3-percpcy5.5 ( bio - legend ) , cd4-fitc ( e - bioscience ) , and cd25-alexafluor700 ( e - bioscience ) .
intracellular stains for foxp3-apc ( e - bioscience ) and rort - pe ( e - bioscience ) were performed using the foxp3 staining buffer set ( e - bioscience ) according to the manufacturer 's instructions .
samples were measured on a fascanto ii flow cytometer with diva software ( bd ) and analyzed with kaluza software ( beckman coulter ) .
t lymphocytes were selected as cd45+cd3 + . among this population , tregs were defined as cd4+cd25+foxp3 + and th17 cells as cd4+rort++ .
the different populations were defined as the level of the positive population above the 99th percentile of a fluorescence - minus - one ( fmo ) sample .
after fixation and sectioning , the liver tissue samples were stained with haematoxylin - eosin and trichrome - masson .
steatosis , lobular inflammation , and ballooning were scored in a blinded way by one single experienced hepatologist according to the nash clinical research network scoring system .
the nash activity score ( nas ) was calculated as the sum of the scores for steatosis , ballooning , and lobular inflammation .
nash was diagnosed if some degree of steatosis , lobular inflammation , and ballooning were simultaneously present [ 24 , 25 ] .
total rna was extracted from stored frozen liver samples using the column - based technique ( rneasy minikit , qiagen , kj venlo , netherlands ) , according to the manufacturer 's instructions .
the total rna extraction for the sat and aat samples was based on the trizol ( invitrogen , life technology , belgium ) procedure from w. m. keck foundation biotechnology microarray resource laboratory at yale university .
purified total rnas were treated with dnase to obtain dna - free rna ( turbo dnase free , ambion , life technology , belgium ) .
cdna was synthesized using a transcriptor first strand cdna synthesis kit ( roche applied science , indianapolis , in ) .
taqman gene expression assay for il10 ( life technologies , belgium , gene i d 16153 , reference mm00439614_m1 ) , il17a ( life technologies , belgium , gene i d 16171 , reference mm00439618_m1 ) , and leptin ( gene i d 16846 , reference mm00434759_m1 ) was performed on an abi prism 7300 sequence detector system ( applied biosystems , life technology , belgium ) in 25 l reaction volumes containing 2 l cdna and 23 l master mix .
the master mix was prepared using 12.5 l taqman universal pcr master mix ( life technologies , belgium ) , 1.25 l primer , and 9.25 l rnasednase free water ( gibco , life technologies , belgium ) .
the parameter for pcr amplification was followed by 50 cycles of 95c for 15 s ( denaturation ) and 60c for 1 minute ( annealing and extension ) .
glyceraldehyde 3-phosphate dehydrogenase ( gadph ) was used as a housekeeping gene to normalize the results ( life technologies , belgium , gene i d 14433 , reference mm99999915_g1 ) .
the ct value corresponds to the number of cycles to reach a defined threshold and therefore it increases with a decreasing amount of the template .
alanine aminotransferase ( alt ) was measured by means of enzyme - linked immunosorbent assay ( elisa ) .
the mann - whitney u test and student 's t - test were used to compare independent variables , as appropriate .
liver histology showed steatosis , lobular inflammation , and ballooning in the mice fed hfd and therefore confirmed the presence of nash .
moreover the blood tests showed higher fasting glucose levels and alt levels in the hfd group in comparison with the nd group .
these data confirmed the validity of the experimental model to obtain hfd - induced nash together with an impairment of glucose metabolism and obesity - like disturbances .
no modifications in the percentage of leukocytes ( cd45 + cells ) , t - lymphocytes ( cd45+cd3 + cells ) , and cd4 + t - lymphocytes were found in mice fed a hfd in comparison with the lean counterparts , except for a decrease of the cd4 + in the aat after hfd .
tregs were significantly increased in the sat of mice fed hfd versus mice fed nd ( p = 0.02 ) , while no difference was found in aat or liver ( figure 2(a ) ) . moreover ,
an increase of the percentage of the highly polarized th17 ( cd4+rort++ ) was detected in the liver ( p = 0.02 ) and the aat ( p = 0.01 ) of mice fed hfd , in comparison with mice fed nd ( figure 2(a ) ) .
rt - pcr showed a positive cytokine response to hfd : both il10 and il17a were expressed in liver ( ct values , resp .
, 15.5 ( 15.416.5 ) and 21.7 ( 21.222.3 ) ) and both the aat ( resp . , 10.8 ( 5.110.9 ) and 8 ( 6.98.2 ) ) and the sat ( resp . ,
11.3 ( 811.7 ) and 6.4 ( 5.56.9 ) ) of mice fed hfd , while they were nondetectable in mice fed nd .
moreover leptin gene expression was increased in the adipose tissue of mice fed hfd compared to mice fed nd .
this increase was more pronounced in the sat district : in the abdominal district leptin increased 2-fold versus 986-fold in the sat ( figure 2(b ) ) .
in addition the significant correlations ( table 3 ) between the t - cell modifications and metabolic parameters and histology were investigated .
the aat - derived cd4+rort++ cells positively correlated with the weight gain and with liver histology : a positive correlation was detected with the nas as well as with its subscores steatosis , ballooning , and lobular inflammation .
moreover the sat - derived tregs positively correlated with the weight gain , the glucose levels , and liver histology ( nas , ballooning , and inflammation ) ( table 3 ) .
there is a growing interest in the role of the immune system as a key contributor to the pathogenesis of nash and the metabolic syndrome .
given the discordant data on the role of tregs and th17 in the development of nash , we performed a study to further elucidate the differential role of these subsets of cells at the different anatomical sites involved in the pathogenesis of nash and we analyzed the correlation between the tissue specific variations of these cells and the diet - induced metabolic disturbances .
the histologic features fulfilled the histologic criteria for nash ( defined as the simultaneous presence of steatosis , inflammation , and ballooning ) .
moreover the mice fed a hfd were obese and showed an impaired glucose tolerance and a leptin upregulation .
our model hence mimics all features of human nash [ 27 , 28 ] . when considering the different organs investigated ( figure 3 ) , the liver showed an increase of cd4+rort++ cells in mice fed a hfd in comparison with mice fed a nd , while there was no difference in tregs .
thus , the balance between th17 and tregs in the liver was shifted towards th17 .
importantly , the increase in cd4+rort++ cells showed a correlation with liver inflammation ( which is an important determinant of liver damage in nash ) , but not with metabolic disturbances . in the aat ,
similar to the liver , we observed an increase of the cd4+rort++ in the mice fed a hfd , while tregs did not show statistically significant variations .
also in this organ hfd shifted the balance between th17 and th10 towards the th17 . in line with the active role of the aat in the onset of nash and of the metabolic syndrome , the aat cd4+rort++ correlated with liver histology as well as with some features of metabolic impairment , including weight gain . in the sat
the tregs played a predominant role as we observed no statistically significant variations of the cd4+rort++ while the tregs were significantly increased in the mice fed a hfd .
this increase correlated with liver histology impairment and with metabolic alterations , namely , glucose impairment and weight gain .
as far as the th17 are concerned , our results are in agreement with tang et al . , who demonstrated an increased number of hepatic th17 and an increased hepatic gene expression in a hfd mouse model , as well as an attenuation of the lps - induced liver injury after neutralization of il17 .
others , however , found a decrease of th17 in the aat of mice fed hfd .
moreover , in an il17-deficient mouse model il17 appeared to act as a negative regulator of adipogenesis and glucose metabolism and to delay the development of diet - induced obesity .
this discrepancy could be explained by the different animal models used . in our model , which was able to represent the main characteristics of human nash , not only in terms of liver histology but also in terms of metabolic impairment , the th17 were increased in the liver and in the aat which are key organs in the onset of nash and positively correlated with liver histology and obesity .
this observation , although it can not mechanistically explain the role of the th17 in nash , suggests that th17 could be key players in nash and the associated metabolic disease . regarding the tregs , previous preclinical studies
reported that aat is a preferential site of accumulation of tregs in mice fed a nd and that they decrease after hfd [ 10 , 29 ] .
others showed an increase of tregs in the sat in obesity [ 29 , 30 ] . in agreement with the latter ,
our data confirm an increase of the tregs specifically in the sat in histologically proven nash accompanied by metabolic alterations .
these data suggest that also the sat plays an active role in liver disease - related and metabolic - related inflammation .
it could also be speculated that in this hfd model the treg increase in the sat is an attempt to restore the proinflammatory prone th17/treg balance .
finally we found a leptin upregulation in mice fed a hfd , mainly in the sat , which , through its systemic effect , may have contributed to the stimulation of immune cells , and particularly the th17 , at distance .
it is known that leptin is able to stimulate the th17 pathway : in experimental conditions of leptin deficiency , lower levels of il17 and an impairment of the th17 pathway are observed while the administration of increasing doses of leptin is able to restore and increase the th17 pathway .
this process could explain , at least in part , the increase of the cd4+rort++ cells in the aat and the liver as a consequence of increased levels of circulating leptin , mainly originating from the sat . in addition leptin has shown proinflammatory , profibrogenic , and prodiabetogenic effects .
this is in line with our observation of a significant correlation between leptin and the alt levels and hepatocellular ballooning , highlighting the link between leptin disturbances and hepatocellular damage . in line with the ability of leptin to stimulate the inflammatory immune response
, we found an upregulation of mrna of il17a in the liver and adipose tissue of mice fed hfd .
these results nicely fit with the aforementioned observed increase of cd4+rort++ in the liver and the abdominal adipose tissue .
in contrast to what could be expected , however , this increase in the proinflammatory il17a was not counterbalanced by a decrease of the il10 mrna in the same sites .
moreover we observed a positive correlation between adipose tissue - derived il10 and hepatic inflammation at histology .
its role , however , in diet - induced steatohepatitis and insulin resistance is controversial .
although il10 has been reported to be protective against diet - induced insulin resistance , it has also been reported that il10 does not improve hepatic or systemic insulin sensitivity in high fat feeding and therefore it does not protect against insulin resistance .
in contrast to the flow - cytometric data , the gene expression analysis showed a cytokine upregulation in the liver and in both the aat and sat . this discrepancy can be explained by the contribution to cytokine secretion by other cell types , which can not be discriminated by this method .
il10 increase could be explained , at least in part , due to a tissue - recruitment of m2 macrophages in response to hfd , as previously described .
il17a on the other hand can be produced by cell types other than th17 , such as nkt and t lymphocytes . given the active role of these cells in the onset of nash and the correlated metabolic disease [ 39 , 40 ] , it could be speculated that also these cells constitute a source of il17 . in conclusion
our results show a stimulation of both the th17 and the treg axis in nash , also in correlation with its metabolic complications .
these pathways seem to act differently at different sites , the th17 axis being upregulated at the level of the aat and the liver , and the treg axis being upregulated in the sat .
it has recently been shown that sat expresses genes that are implicated in inflammation that correlate with liver damage and is therefore also potentially implicated in nash pathogenesis .
the treg upregulation in sat observed in our study could hence be as a tentative to increase the anti - inflammatory mechanisms in response to inflammation and , therefore , it could represent a compensatory mechanism to counterbalance the th17 enhancement .
furthermore , obesity - related overproduction of leptin in sat could be one of the drivers of the upregulation of the th17 pathway , further highlighting the potential contribution of the sat , besides that of the aat .
as this is , however , a cross - sectional study , it is not possible to draw clear cause - effect conclusions . |
background and aims .
inflammatory mediators that cross - talk in different metabolically active organs are thought to play a crucial role in the pathogenesis of nonalcoholic steatohepatitis ( nash ) .
this study was aimed at investigating the cd4+rort+ t - helper cells and their counterpart , the cd4+cd25+foxp3 + regulatory t cells in the liver , subcutaneous adipose tissue ( sat ) , and abdominal adipose tissue ( aat ) in a high fat diet ( hfd ) mouse model .
methods .
c57bl6 mice were fed a hfd or a normal diet ( nd ) .
liver enzymes , metabolic parameters , and liver histology were assessed .
the expression of cd4+rort+ cells and regulatory t cells in different organs ( blood , liver , aat , and sat ) were analyzed by flow cytometry .
cytokine and adipokine tissue expression were studied by rt - pcr .
results .
mice fed a hfd developed nash and metabolic alterations compared to normal diet .
cd4+rort++ cells were significantly increased in the liver and the aat while an increase of regulatory t cells was observed in the sat of mice fed hfd compared to nd .
inflammatory cytokines were also upregulated .
conclusions .
cd4+rort++ cells and regulatory t cells are altered in nash with a site - specific pattern and correlate with the severity of the disease .
these site - specific differences are associated with increased cytokine expression . | 1. Introduction
2. Materials and Methods
3. Results
4. Discussion |
two proven vector control strategies are currently advocated to reduce transmission of malarial disease in africa , namely indoor residual spraying ( irs ) [ 1 - 5 ] and insecticide - treated bednets ( itns ) [ 6 - 9 ] . both methods are based on the use of residual insecticides in the intra - domiciliary domain and target mosquito vectors either before ( itns ) or after host - feeding ( irs ) .
impressive reductions in childhood morbidity and mortality have been demonstrated in a variety of epidemiological settings , and it can be expected that irs / itns will remain in the forefront of malaria vector control for at least the remainder of this decade . in spite of their proven effectiveness [ 5 - 9 ] ,
both methods have some drawbacks and limitations , such as insecticide resistance [ 10 - 13 ] , environmental or human health concerns and socio - economic or cultural acceptance by communities .
it is also clear that these powerful tools are not sufficient on their own to eliminate or drastically reduce the malaria burden from the most intensely endemic regions of the tropics , notably sub - saharan africa .
an expansion of this limited arsenal of vector - control tools , with new strategies to reduce human exposure , the size of mosquito populations , or transmissibility of disease , is therefore needed , and preferably appropriate for use in an integrated fashion with irs / itns [ 19 - 21 ] .
new innovative strategies , involving the release of genetically - engineered mosquitoes , aimed at rendering vector populations less susceptible to infection by human pathogens have seen enormous developments over the past few years [ 22 - 27 ] . if transposable genetic elements can be used to drive genes coding for refractoriness into fixation in wild vector populations , a substantial reduction in disease transmission may result .
however , advances to date have been confined to laboratory settings and many questions relating to the fitness , behaviour , ecology and phenotypic characteristics of transformed insects remain unanswered [ 27 - 29 ] .
the spread of desired traits , such as refractoriness to plasmodium infection , will depend on the reproductive fitness , evolutionary cost of the introduced trait , and manifestation of life - history behaviours , such as dispersal and mating , by engineered specimens .
for instance , given the likelihood of assortative mating , transgenic males and females may face strong competition upon release , which necessitates an increased understanding of the behavioural and ecological determinants of gene flow in mosquito populations . the characteristics of genetically - engineered mosquitoes should preferably be similar to those of their wild con - specifics but may be compromised by genetic modification , selection for specific traits or routine laboratory maintenance and difficult to assess realistically under standard laboratory conditions .
many of the ecological and population biology issues thus remain serious challenges to the application of genetically - engineered mosquitoes .
moreover , until such time that the probability of potential public health benefits can be maximised , it will be unlikely that approval for release can and will be granted .
the use of large contained field - based research settings is now widely advocated to face the shortfalls in our understanding of the behaviour and ecology of genetically - engineered vectors , prior to their release in the wild .
contained semi - field systems have been used for a variety of studies on mosquitoes , albeit outside africa [ 37 - 40 ] . in kenya , we have recently rejuvenated this approach and developed semi - field systems to study the behavioural ecology of malaria vectors [ 32,41 - 44 ] . by doing so
we present the first attempts to complete the life - cycle of this important vector in such systems , as a first step towards studies involving genetically - engineered specimens .
we transformed an existing greenhouse ( cambridge glass house co. ltd . , uk ) , measuring 11.4 7.1 m ( fig .
1a,1b,1c,1d ) into a ' malariasphere ' ( an enclosed environment with all components of a natural anopheles ecosystem ) by replacing all glass parts with dark - green shade netting ( density 90% ) permitting airflow ( wind ) and precipitation to enter the system . consequently ,
a sliding door provides entrance to the sphere , after passing a double layer of similar shade netting to prevent escape of released mosquitoes and entry of wild ones .
the sphere is located on the shores of lake victoria , west kenya at the mbita point research & training centre ( 0025 's , 3413'e ) of the international centre of insect physiology and ecology ( icipe ) .
the area experiences two rainy seasons ; the long rains from mid - march through june and short rains from october through december .
relatively high temperatures prevail throughout the year , ranging from 16c to 34c . during the rainy season , there are ample breeding sites in the mbita area for an .
suba district is inhabited by some 156,000 people , mostly belonging to the luo ethnic group , who practice mainly fishing and subsistence farming .
; data - loggers are shown as grey cubes ) and photographs of the hut ( b , note the white arrow showing the breeding site in front of the hut ( c , d ) .
further details see text . inside the sphere , a traditional luo house ( 3.2 2.8 1.7 m , fig .
a mixture of wood ash and clay was used for plastering and smoothing the wall surfaces .
the roof ( 2.8 m at its apex ) was made of grass thatch mounted on a wooden frame .
the house has a single door and no windows , which is typical for a local ' simba ' house .
eaves ( height 15 cm ) all around provide ventilation and serve as the predominant entry point for mosquitoes .
we maintained the depth of the site at 15 cm by replenishing it with water collected from lake victoria .
in each site we suspended a hobooptic stowaway tidbit data logger just below the water surface , and recorded the temperature at 30 min intervals . in order to monitor climatic conditions inside the system , we fitted six more hoboh8 data loggers , three inside the hut ( at 0.5 , 1.5 and 2.5 m from ground level ) and three outside the hut on a pole at similar heights ( fig .
climatic data were collected in february ( peak summer ) and june ( onset of the cold season ) .
we allowed plants to emerge from seeds present in the soil brought into the sphere , and in addition to this we planted a variety of food crops normally found around local homesteads ( table 1 ) . prior to the release of mosquitoes and during construction of the house and planting of crops , a wide variety of other organisms entered the sphere , including some known mosquito predators such as ants ( formicidae ) , spiders ( e.g. salticidae ) and geckos ( geckonidae ) .
mosquitoes used in the experiments originates from njage village ( 70 km from ifakara ) , south - east tanzania , and has been maintained under laboratory conditions since april 1996 .
adult insects were kept in standard 30 30 30 cm netting cages and offered 6% glucose as a carbohydrate source .
the cages were kept under ambient climatic conditions and females given the opportunity to feed on an arm of a volunteer for 10 min three times per week .
eggs were collected on wet filter paper disks ( 9 cm diameter ) and transferred to plastic containers containing water from lake victoria .
larvae were fed daily on tetraminfish food . upon pupation , insects were transferred to cages for emergence . in order to assess
whether all major life - history behaviours ( i.e. mating , sugar feeding , host seeking and oviposition ) occurred successfully in the sphere , we attempted to complete the life - cycle during three separate experiments by introducing i ) a group of 100 blood - fed females , ii ) groups of 500 virgin females and 1500 males or iii ) batches of 500 eggs in both breeding sites : i ) in the first experiment we introduced 100 three - day - old females ( f0 ) , which had been held in cages with males since the time of emergence .
they were blood fed ( for the first time ) on the forearm of a volunteer for 15 min and subsequently released ( at 21.30 hrs ) from a paper cup placed on the bed inside the hut .
we then monitored the presence and development of eggs , larvae and pupae by inspecting the breeding sites at daily intervals .
following emergence of the first adults , we deliberately waited for six days before entering the greenhouse at night , in order to assess whether mosquitoes would successfully mate and survive / feed on the plants in the system . on day 17
, 19 , 20 and 21 following the introduction of females , a volunteer slept inside the hut from 21.30 hrs until 07.00 the following day , which allowed the f1 population , and any of their parents that had survived , to feed on human blood .
ii ) as some of the parental ( f0 ) females could have survived until day 17 , it needed to be ascertained that virgin ( newly emerged ) insects survived , mated and blood - fed successfully too .
we therefore introduced 500 , 3 to 5 day - old virgin females , which had emerged from the pupa individually in glass vials , together with 1500 , 5 to 7 day - old males at 21.00 hrs .
starting three days afterwards , a volunteer slept in the hut for 5 consecutive nights .
we observed daily whether eggs were laid in the breeding sites to ensure that insemination , blood feeding and oviposition had taken place for two weeks following the release .
all pupae were collected from the breeding sites as they appeared so that assessments of survival by the f0 generation would not be confounded by the emergence of an overlapping f1 generation .
iii ) a third experiment was started by introducing 500 eggs at night ( 22.30 hrs ) in each of the two breeding sites .
concurrently we reared one thousand eggs from the same batch under standard laboratory conditions described above .
this enabled us to determine the sex ratio and thus the number of males and females released .
a volunteer occupied the hut for four consecutive nights , starting on day 22 after the start of the experiment .
thereafter , the breeding sites were monitored daily for the presence of eggs / larvae until day 32 .
a research protocol for the above experiments was submitted to the kenya national ethical review committee , based at the kenya medical research institute ( kemri ) , in which the discomfort and potential risks of ( non - infectious ) mosquito bites to volunteers was explained .
bnn , bgjk and gfk were involved in the experiments , and do not object to their names being revealed for publication .
a parasite - free environment was ensured through a ) regular screening of the volunteers ' peripheral blood for plasmodium parasites and b ) non - occupancy of the sphere beyond 5 days after the mosquitoes were given the first opportunity to obtain a blood meal .
as malaria infections in mosquitoes take at least 10 days to reach the sporozoite - infective stage , this procedure minimised risks of volunteers being infected within the experimental set up .
we transformed an existing greenhouse ( cambridge glass house co. ltd . , uk ) , measuring 11.4 7.1 m ( fig .
1a,1b,1c,1d ) into a ' malariasphere ' ( an enclosed environment with all components of a natural anopheles ecosystem ) by replacing all glass parts with dark - green shade netting ( density 90% ) permitting airflow ( wind ) and precipitation to enter the system . consequently ,
a sliding door provides entrance to the sphere , after passing a double layer of similar shade netting to prevent escape of released mosquitoes and entry of wild ones .
the sphere is located on the shores of lake victoria , west kenya at the mbita point research & training centre ( 0025 's , 3413'e ) of the international centre of insect physiology and ecology ( icipe ) .
the area experiences two rainy seasons ; the long rains from mid - march through june and short rains from october through december .
relatively high temperatures prevail throughout the year , ranging from 16c to 34c . during the rainy season , there are ample breeding sites in the mbita area for an .
suba district is inhabited by some 156,000 people , mostly belonging to the luo ethnic group , who practice mainly fishing and subsistence farming .
; data - loggers are shown as grey cubes ) and photographs of the hut ( b , note the white arrow showing the breeding site in front of the hut ( c , d ) .
further details see text . inside the sphere , a traditional luo house ( 3.2 2.8 1.7 m , fig .
a mixture of wood ash and clay was used for plastering and smoothing the wall surfaces .
the roof ( 2.8 m at its apex ) was made of grass thatch mounted on a wooden frame .
the house has a single door and no windows , which is typical for a local ' simba ' house .
eaves ( height 15 cm ) all around provide ventilation and serve as the predominant entry point for mosquitoes .
we maintained the depth of the site at 15 cm by replenishing it with water collected from lake victoria .
in each site we suspended a hobooptic stowaway tidbit data logger just below the water surface , and recorded the temperature at 30 min intervals . in order to monitor climatic conditions inside the system , we fitted six more hoboh8 data loggers , three inside the hut ( at 0.5 , 1.5 and 2.5 m from ground level ) and three outside the hut on a pole at similar heights ( fig .
climatic data were collected in february ( peak summer ) and june ( onset of the cold season ) .
we allowed plants to emerge from seeds present in the soil brought into the sphere , and in addition to this we planted a variety of food crops normally found around local homesteads ( table 1 ) . prior to the release of mosquitoes and during construction of the house and planting of crops , a wide variety of other organisms entered the sphere , including some known mosquito predators such as ants ( formicidae ) , spiders ( e.g. salticidae ) and geckos ( geckonidae ) .
mosquitoes used in the experiments originates from njage village ( 70 km from ifakara ) , south - east tanzania , and has been maintained under laboratory conditions since april 1996 .
adult insects were kept in standard 30 30 30 cm netting cages and offered 6% glucose as a carbohydrate source .
the cages were kept under ambient climatic conditions and females given the opportunity to feed on an arm of a volunteer for 10 min three times per week .
eggs were collected on wet filter paper disks ( 9 cm diameter ) and transferred to plastic containers containing water from lake victoria .
in order to assess whether all major life - history behaviours ( i.e. mating , sugar feeding , host seeking and oviposition ) occurred successfully in the sphere , we attempted to complete the life - cycle during three separate experiments by introducing i ) a group of 100 blood - fed females , ii ) groups of 500 virgin females and 1500 males or iii ) batches of 500 eggs in both breeding sites : i ) in the first experiment we introduced 100 three - day - old females ( f0 ) , which had been held in cages with males since the time of emergence .
they were blood fed ( for the first time ) on the forearm of a volunteer for 15 min and subsequently released ( at 21.30 hrs ) from a paper cup placed on the bed inside the hut .
we then monitored the presence and development of eggs , larvae and pupae by inspecting the breeding sites at daily intervals .
following emergence of the first adults , we deliberately waited for six days before entering the greenhouse at night , in order to assess whether mosquitoes would successfully mate and survive / feed on the plants in the system . on day 17 , 19 , 20 and 21 following the introduction of females , a volunteer slept inside the hut from 21.30 hrs until 07.00 the following day , which allowed the f1 population , and any of their parents that had survived , to feed on human blood .
ii ) as some of the parental ( f0 ) females could have survived until day 17 , it needed to be ascertained that virgin ( newly emerged ) insects survived , mated and blood - fed successfully too .
we therefore introduced 500 , 3 to 5 day - old virgin females , which had emerged from the pupa individually in glass vials , together with 1500 , 5 to 7 day - old males at 21.00 hrs .
starting three days afterwards , a volunteer slept in the hut for 5 consecutive nights .
we observed daily whether eggs were laid in the breeding sites to ensure that insemination , blood feeding and oviposition had taken place for two weeks following the release .
all pupae were collected from the breeding sites as they appeared so that assessments of survival by the f0 generation would not be confounded by the emergence of an overlapping f1 generation .
iii ) a third experiment was started by introducing 500 eggs at night ( 22.30 hrs ) in each of the two breeding sites .
concurrently we reared one thousand eggs from the same batch under standard laboratory conditions described above .
this enabled us to determine the sex ratio and thus the number of males and females released .
a volunteer occupied the hut for four consecutive nights , starting on day 22 after the start of the experiment .
thereafter , the breeding sites were monitored daily for the presence of eggs / larvae until day 32 .
a research protocol for the above experiments was submitted to the kenya national ethical review committee , based at the kenya medical research institute ( kemri ) , in which the discomfort and potential risks of ( non - infectious ) mosquito bites to volunteers was explained .
bnn , bgjk and gfk were involved in the experiments , and do not object to their names being revealed for publication .
a parasite - free environment was ensured through a ) regular screening of the volunteers ' peripheral blood for plasmodium parasites and b ) non - occupancy of the sphere beyond 5 days after the mosquitoes were given the first opportunity to obtain a blood meal . as malaria infections in mosquitoes
take at least 10 days to reach the sporozoite - infective stage , this procedure minimised risks of volunteers being infected within the experimental set up .
figure 2 shows the climatic conditions recorded in the greenhouse over a 3-week period in june 2000 , coinciding with the time of the third experiment ( onset cold dry season ) .
similar data sets for february 2000 ( peak of the main hot and dry season ) showed an average temperature at the water surface of 24.0c ( range 20.029.8c ) .
other studies have recorded slightly lower average temperatures and larger ranges over which these fluctuate , both in artificially constructed and natural sites .
haddow recorded a range of 19.034.5c in pans of similar size that were supplemented with soil and had water of similar depth near kisumu ( 80 km from mbita point ) .
gimnig et al . recorded an average of 26.4 0.7c from natural sites between march and august 1998 in that same area , as did koenraadt et al .
( pers . comm . ) , with 25.8 4.2c , in two subsequent years .
the lower temperatures recorded from sites in the sphere were probably caused by reduced infiltration of sunlight through the roof 's shade netting .
temperature ( a ) and relative humidity ( b ) data recorded in one of the two the breeding sites and different heights ( 0.5 , 1.5 and 2.5 m ) inside the hut over a 3-week period in june 2000 . arrows on y - axis show maximum and minimum recorded and accompanying figures show the same data for data - loggers outside the hut at those same heights .
2a ) inside the hut at various heights fluctuated much more considerably but nevertheless remained relatively consistent throughout the observational periods .
average temperatures increased both inside ( 23.1 , 23.8 and 23.9c for 0.5 , 1.5 and 2.5 m respectively ) and outside the hut with height as did the range over which these fluctuated daily . corresponding data for february inside the hut showed higher averages ( 24.8 , 25.1 and 25.2c for 0.5 , 1.5 and 2.5 m respectively ) .
between the seasons , maximum variation between temperatures was found outside the hut at 2.5 m , from 37.0c ( february - maximum ) to 16.4c ( june - minimum ) .
the smallest variation was observed inside the hut at 0.5 m , from 28.7c ( february - maximum ) to 19.7c ( june - minimum ) . as such
, the range over which temperatures fluctuated between seasons was 2.3 times larger outside ( 2.5 m ) than inside ( 0.5 m ) the hut .
haddow recorded mean temperatures between october and december in local huts ( at 1 m height ) in the kisumu area and found an average temperature of 24.2c ( range 21.027.0c ) .
our own measurements inside the hut in the sphere between 18 october and 15 november ( 2000 ) at 1.5 m height gave values of 24.0 1.76c ( range 19.829.1c ) whereas measurements inside 4 local houses in mbita of similar design during that same period gave higher average values ( 0.50.8c ) and absolute maxima ( 0.8c ) .
ambient conditions inside local houses are more constant than outdoor climatic conditions ( this study and ) and it would seem that the sphere itself exerts a similar , albeit small , insulating effect : slightly lower temperatures and smaller ranges over which these fluctuate , both inside and outside the hut . relative humidity ( rh ) data ( fig .
relative humidity is fairly constant and averages inside the hut during june ranged from 63.5% ( 1.0 m ) to 69.3% ( 2.5 m ) .
minimum values were always higher inside the hut than outside , providing more suitable microclimatic conditions for resting mosquitoes .
measurements in october / november , both in the sphere and a local house of similar design in mbita point , showed slightly higher average rh values outdoors in both settings than indoors with minimal differences between the sphere and the village hut .
overall , as with temperatures , the range over which the rh fluctuated was smaller inside than outside the hut and minima inside the sphere were always 3 to 4 % higher than those measured in village huts .
although small , these climatic differences may affect development of immature stages and survival of adults , and research findings from experiments inside the sphere should be compared with field conditions at slightly higher altitudes .
the introduction of blood - fed females into the greenhouse resulted in the presence of eggs in the breeding sites on day 3 ( 2.5 days after release ) , and eggs continued to be observed in the sites until day 7 ( fig .
3 ) . larvae ( from l1 to l4 stage ) were seen feeding at the water surface until day 23 , when the last l4 larva pupated .
the first five pupae were seen in the breeding sites in the evening of day 10 , meaning that the variation in maturation time from egg to pupa was 720 days . in spite of having conditions with higher larval density and smaller water surface area , gimnig et al . recorded much reduced periods to pupation , from 5 to 12 days . in total , 57 pupae were counted in the breeding site 3.8 m in front of the hut and 130 in the site 1.1 m behind it , and on average they harboured only 0.08 and 0.18 larva / cm , respectively .
these densities are lower than those observed in natural habitats , and given the fact that we observed algal growth , considered important for larval growth , it seems that the prolonged time to pupation in this trial may be attributed to the relatively small range over which temperatures fluctuate .
alternatively , re - introducing mosquitoes that had been maintained under laboratory conditions for several years in a more natural setting may have caused these effects , and poor adaptation to these conditions may have stunted their development .
completion of the anopheles gambiae life - cycle in the greenhouse over a 27-day period .
blood - fed females were released on day 1 , and arrows show time periods during which the various developmental stages were observed .
the first adults were seen inside the hut on day 11 , and continued to be present until the end of the experiment ( day 27 ) .
starting in the morning of day 22 , we observed new eggs in the breeding sites and subsequent larval development . from the above it
can be deduced that specific behaviours of the adult insects occurred during certain time periods ( fig .
oviposition activity took place twice during this trial , meaning that females survived until eggs were mature , that they successfully located a breeding site , accepted it for oviposition , and laid eggs .
other potential breeding sites , like the leaf axils of the banana trees in the sphere , were examined but were not found to harbour eggs , larvae or pupae .
the period for reaching sexual maturity for males may be at least one day and for females up to 60 hrs , so mating of the f1 generation may not have taken place until dusk on day 14 . in spite of regular observations during dusk , we did not see any swarming activity typically associated with mating in an .
this is a particularly interesting point , because in contrast with other settings ( e.g. ) , where mating swarms were frequently observed we failed to do so over a 3-year period in the mbita area as did charlwood ( pers.comm . ) who observed only one anopheline swarm during 4 years in the kilombero valley of tanzania , raising the question as to whether swarming is an obligate component of the an .
alternatively , maintenance of mosquitoes in laboratory cages for several years forced this strain to become stenogamous ( i.e. the ability to mate in small cages ) , and this adaptation may have interfered with its ability to swarm when introduced into the sphere . as newly emerged adults rarely survive for more than 48 hrs without the availability of an energy source , mosquitoes must have supplemented their energy reserves with carbohydrates from the plants in the sphere ( table 1 ) for up to 6 days before they were allowed access to a blood source , in the form of a human volunteer sleeping in the hut .
some plants like castorbean ( ricinus communis l. ) were flowering at the time of the experiment , and may have provided nectar sources . in cage experiments ( impoinvil et al . , in prep . )
we have observed a mean survival time of 7.0 0.2 days on this plant , which is comparable to mosquitoes given 6% glucose ( 8.7 0.2 days ) .
gambiae mosquitoes emerge from the pupal stage with a deficit not only in carbohydrates , but also lipid and protein , which usually is compensated for by consuming a ( small ) blood meal within the first few days of adult life , it is likely that mortality during the 6-day post - emergence period in the current trial was too high to have a good number of the 8090 females that emerged survive long enough to obtain their first blood meal . within 15 min of entering the hut at night ,
the volunteer noticed the sound of mosquitoes and subsequently felt mosquito bites on his exposed lower limbs .
this implies that females were receptive to host cues , entered the hut , probably through the eaves , and then successfully located and fed on the human host . at sunrise ,
several engorged females were seen resting on the walls , indicating successful blood feeding and endophily ( indoor resting ) , which is typical for this species . following maturation of eggs ,
the second oviposition began during the night of day 21 , thus completing the life - cycle .
we continued to observe both immature and adult insects ( presumably mostly from the f1 generation ) until day 27 , when the experiment was terminated ( by refraining from entering the sphere for about 1 month ) .
the second experiment , in which we released 500 virgin females together with 1500 males demonstrated that mating does occur in a relatively small , semi - field system .
after the third night that a volunteer had slept in the hut , we observed eggs in the breeding sites .
the production of offspring , though , was low , and we only collected 40 pupae by the end of the trial period .
this may have been caused by heavy rainfall during three consecutive nights ( day 24 ) , which may have affected the survival of the adults and/or larvae or washed away the larvae from the breeding sites due to overflow .
since we observed few mosquitoes , we decided to conduct a human landing catch during two nights inside the hut , starting two nights after sleeping in the hut had ended .
nevertheless , the life - cycle was completed , as manifested by the harvested pupae , which were removed from the breeding sites to prevent emergence of the f1 generation which would have compromised interpretation of survival of the f0 generation .
the third experiment started by introducing 500 eggs into each of the breeding sites , whilst 1000 eggs ( from the same original batch ) were reared under laboratory conditions . in the laboratory , larvae developed at the same rate and
most reached maturity by day 10 , when the first pupae were observed ( fig .
this was similar for the breeding sites in the sphere , except that development was highly asynchronous , i.e. some larvae pupated by day 10 , whereas others took up to day 24 before pupation .
these times to pupation are similar to those observed in the first trial , but are again in contrast with other studies .
on day 7 we counted all larvae and observed 887 in the insectary , as opposed to 652 in the sphere .
overall , the laboratory batch yielded 804 pupae , versus 495 from the breeding sites .
on the basis of these data , the average daily survival was 0.90 for the laboratory larvae , and 0.83 for the larvae in the sphere . with nearly half the larvae surviving to the adult stage , these results contrast sharply with much higher mortalities ( up to 90% ) observed in the kisumu area and so tome ( charlwood , pers .
the sex ratio of emerging adults in the laboratory was 2:3 , which translated into a female population in the sphere of 297 , on the assumption that no insects died during emergence . on day 28 , after the release of eggs in the breeding sites , we observed that eggs had been laid by the f1 generation , but with only 6 and 3 eggs in the two breeding sites respectively .
cumulative percentage of pupation of eggs introduced in the two breeding sites inside the greenhouse ( ) or under insectary conditions ( ) .
our results have shown that by starting either at the post - blood feeding , pre - mating , or egg stage , a new generation of insects can be reared under these semi - field conditions , and that all life - history behaviours were successfully completed to a lesser or greater extent .
this therefore represents the first and promising step towards continuous maintenance of parasite - free an .
gambiae populations under semi - natural conditions that can be experimentally manipulated in studies of malaria vector ecology and transmission control .
russell and rao used a large outdoor cage , based on a design by hackett and bates , to study swarming and oviposition behaviour of an .
culicifacies giles in india , and showed that such systems can be used to unravel aspects of the behavioural ecology of anophelines .
our study shows that such systems can now also be developed for studies on african malaria vectors in order to start filling the gaps in our understanding of the behavioural ecology of these insects .
first and foremost , it provides a suitable intermediate between laboratory - based studies addressing mosquito behaviour and ecology , and the field situation .
too often , conclusions are drawn from results obtained under laboratory conditions that necessitate speculation as to what may or may not happen in the field .
fixed climatic conditions , cage - experiments , olfactometers and windtunnels , in which the mosquito strains used have been laboratory - reared for sometimes decades , may readily distort behavioural and ecological phenomena .
here we have shown that , beyond introducing f1 generation malaria - free mosquitoes from wild populations , it may be possible to rear vectors in situ within a semi - natural system that may minimize such artefacts .
conversely , the advantage of using insectary - reared mosquitoes is in the level of control that may be exerted that would not otherwise be possible : experiments can be conducted all - year - round , with fixed numbers of insects , of known age and physiological status , in a malaria parasite - free environment under ambient climatic conditions . this enables more direct inferences to be drawn from data analysis as compared to longitudinal field studies , because of constant conditions and simplified experimental design .
we have recently evaluated the efficacy of several plants traditionally used by the luo community as repellents in a similar semi - field set - up , and simple logistic regression , on data collected during four nights per plant , yielded significant results . within a year of nearly continuous experimentation
, the repellency of 8 plant species and 3 combinations thereof was evaluated through thermal expulsion or direct burning , and 9 species and 2 combinations thereof were tested in potted form .
such studies would have taken several years under field conditions , and would be limited to times when mosquito densities would have been sufficiently high to permit meaningful experiments .
gambiae maintained on a variety of diets ( blood or sugar alone , or a combination of both ) and revealed similar results to those obtained under laboratory conditions .
within one year of starting studies on the behaviour of mosquitoes around bednets in a semi - field setup , we transformed a regular conical bednet into a trap that may catch up to 70% of the females released .
recent field evaluation of this trap shows it to be a promising replacement for the human landing catch ( mathenge et al .
with the trap now being considered for commercial manufacturing ( it took a mere two years to reach this stage ) , this would have been impossible without the availability of a semi - field set - up in which continuous experimentation ensured rapid progress towards product development .
even though our system resembles more closely the field situation , it remains to be ascertained to what extent .
our current study was mainly qualitative in design and focused on life - cycle completion .
for instance , observation of eggs in the breeding sites in the morning of day 22 during the first trial implies that these originated from females that fed once on day 19 , as those that fed on day 17 should have laid before .
however , it is likely that these females fed twice , on day 17 and day 19 , and should be classified as pre - gravids , before fully maturing a batch of eggs
. furthermore , in the absence of a human host , mosquitoes survived up to six days after emergence , confirming field results that feeding on plant sugars does occur and may be an important feature of the life - cycle in this species ( foster and knols , unpublished data ) .
there may be other , yet unknown , factors that affect the behavioural ecology of the insects in such systems . or , as bates wrote , following his outdoor cage studies in albania : " one still can not be sure that the reactions of the mosquito are ' natural ' because there is always the barrier of wire liable to be encountered on extended flights ; and when the flight of a mosquito has been interrupted by this wire barrier its further activity may be definitely unnatural " .
rightly so , and even though we did not observe any obvious distorted behaviours , it is imperative that findings from semi - field studies be verified under natural outdoor conditions
. additional studies in which the release and performance of field - collected , blood - fed mosquitoes in the sphere is compared with that of laboratory specimens in terms of egg - recovery , developmental periods and important behavioural characteristics ( like swarming ) will provide further insight to what extent such systems mimic the natural anopheles environment and colony adaptation impairs natural behaviours . nevertheless , since bates ' days , advances in science merit a renewed impetus towards semi - field studies in contained near - natural environments , particularly with respect to transgenic mosquitoes .
fitness evaluations of engineered strains of vectors are mandatory for transformation technology to become an established disease control tool in africa . perhaps this alone , is ample justification for more intensive sphere studies , hopefully not only in kenya , but also in other african countries likely to be involved in this endeavour .
studies on gene flow , mating behaviour and reproductive fitness , combined with studies on the effects of laboratory maintenance on the genetic make - up of transformed strains to be released , can be conducted in semi - field systems .
such systems , particularly when used to study genetically - engineered mosquitoes will require more advanced containment levels than the system described here . guidelines for facility location , physical and biological containment , safety practices and calamity control need to be developed and adapted from existing arthropod containment guidelines .
there are several good reasons to further such studies in disease - endemic settings . under such conditions it will be possible to transform offspring from wild mosquitoes , conduct experiments under local ambient climatic conditions and evaluate transgene spread and fixation in offspring from field - collected gravid females that emerge in a semi - field setup .
last , but not least , it will enable scientists from developing countries to become more directly involved in evaluating the potential use and application of transgenic mosquitoes for future malarial disease control .
figure 2 shows the climatic conditions recorded in the greenhouse over a 3-week period in june 2000 , coinciding with the time of the third experiment ( onset cold dry season ) .
similar data sets for february 2000 ( peak of the main hot and dry season ) showed an average temperature at the water surface of 24.0c ( range 20.029.8c ) .
other studies have recorded slightly lower average temperatures and larger ranges over which these fluctuate , both in artificially constructed and natural sites .
haddow recorded a range of 19.034.5c in pans of similar size that were supplemented with soil and had water of similar depth near kisumu ( 80 km from mbita point ) .
gimnig et al . recorded an average of 26.4 0.7c from natural sites between march and august 1998 in that same area , as did koenraadt et al .
( pers . comm . ) , with 25.8 4.2c , in two subsequent years .
the lower temperatures recorded from sites in the sphere were probably caused by reduced infiltration of sunlight through the roof 's shade netting .
temperature ( a ) and relative humidity ( b ) data recorded in one of the two the breeding sites and different heights ( 0.5 , 1.5 and 2.5 m ) inside the hut over a 3-week period in june 2000 . arrows on y - axis show maximum and minimum recorded and accompanying figures show the same data for data - loggers outside the hut at those same heights .
2a ) inside the hut at various heights fluctuated much more considerably but nevertheless remained relatively consistent throughout the observational periods .
average temperatures increased both inside ( 23.1 , 23.8 and 23.9c for 0.5 , 1.5 and 2.5 m respectively ) and outside the hut with height as did the range over which these fluctuated daily . corresponding data for february inside the hut showed higher averages ( 24.8 , 25.1 and 25.2c for 0.5 , 1.5 and 2.5 m respectively ) .
between the seasons , maximum variation between temperatures was found outside the hut at 2.5 m , from 37.0c ( february - maximum ) to 16.4c ( june - minimum ) .
the smallest variation was observed inside the hut at 0.5 m , from 28.7c ( february - maximum ) to 19.7c ( june - minimum ) . as such
, the range over which temperatures fluctuated between seasons was 2.3 times larger outside ( 2.5 m ) than inside ( 0.5 m ) the hut .
haddow recorded mean temperatures between october and december in local huts ( at 1 m height ) in the kisumu area and found an average temperature of 24.2c ( range 21.027.0c ) .
our own measurements inside the hut in the sphere between 18 october and 15 november ( 2000 ) at 1.5 m height gave values of 24.0 1.76c ( range 19.829.1c ) whereas measurements inside 4 local houses in mbita of similar design during that same period gave higher average values ( 0.50.8c ) and absolute maxima ( 0.8c ) .
ambient conditions inside local houses are more constant than outdoor climatic conditions ( this study and ) and it would seem that the sphere itself exerts a similar , albeit small , insulating effect : slightly lower temperatures and smaller ranges over which these fluctuate , both inside and outside the hut . relative humidity ( rh ) data ( fig .
relative humidity is fairly constant and averages inside the hut during june ranged from 63.5% ( 1.0 m ) to 69.3% ( 2.5 m ) .
minimum values were always higher inside the hut than outside , providing more suitable microclimatic conditions for resting mosquitoes .
measurements in october / november , both in the sphere and a local house of similar design in mbita point , showed slightly higher average rh values outdoors in both settings than indoors with minimal differences between the sphere and the village hut .
overall , as with temperatures , the range over which the rh fluctuated was smaller inside than outside the hut and minima inside the sphere were always 3 to 4 % higher than those measured in village huts .
although small , these climatic differences may affect development of immature stages and survival of adults , and research findings from experiments inside the sphere should be compared with field conditions at slightly higher altitudes .
the introduction of blood - fed females into the greenhouse resulted in the presence of eggs in the breeding sites on day 3 ( 2.5 days after release ) , and eggs continued to be observed in the sites until day 7 ( fig .
3 ) . larvae ( from l1 to l4 stage ) were seen feeding at the water surface until day 23 , when the last l4 larva pupated .
the first five pupae were seen in the breeding sites in the evening of day 10 , meaning that the variation in maturation time from egg to pupa was 720 days . in spite of having conditions with higher larval density and smaller water surface area , gimnig et al . recorded much reduced periods to pupation , from 5 to 12 days . in total , 57 pupae were counted in the breeding site 3.8 m in front of the hut and 130 in the site 1.1 m behind it , and on average they harboured only 0.08 and 0.18 larva / cm , respectively .
these densities are lower than those observed in natural habitats , and given the fact that we observed algal growth , considered important for larval growth , it seems that the prolonged time to pupation in this trial may be attributed to the relatively small range over which temperatures fluctuate .
alternatively , re - introducing mosquitoes that had been maintained under laboratory conditions for several years in a more natural setting may have caused these effects , and poor adaptation to these conditions may have stunted their development .
completion of the anopheles gambiae life - cycle in the greenhouse over a 27-day period .
blood - fed females were released on day 1 , and arrows show time periods during which the various developmental stages were observed .
the first adults were seen inside the hut on day 11 , and continued to be present until the end of the experiment ( day 27 ) .
starting in the morning of day 22 , we observed new eggs in the breeding sites and subsequent larval development . from the above it
can be deduced that specific behaviours of the adult insects occurred during certain time periods ( fig .
oviposition activity took place twice during this trial , meaning that females survived until eggs were mature , that they successfully located a breeding site , accepted it for oviposition , and laid eggs .
other potential breeding sites , like the leaf axils of the banana trees in the sphere , were examined but were not found to harbour eggs , larvae or pupae . the period for reaching sexual maturity for
males may be at least one day and for females up to 60 hrs , so mating of the f1 generation may not have taken place until dusk on day 14 . in spite of regular observations during dusk , we did not see any swarming activity typically associated with mating in an .
this is a particularly interesting point , because in contrast with other settings ( e.g. ) , where mating swarms were frequently observed we failed to do so over a 3-year period in the mbita area as did charlwood ( pers.comm . ) who observed only one anopheline swarm during 4 years in the kilombero valley of tanzania , raising the question as to whether swarming is an obligate component of the an .
alternatively , maintenance of mosquitoes in laboratory cages for several years forced this strain to become stenogamous ( i.e. the ability to mate in small cages ) , and this adaptation may have interfered with its ability to swarm when introduced into the sphere . as newly emerged adults rarely survive for more than 48 hrs without the availability of an energy source , mosquitoes must have supplemented their energy reserves with carbohydrates from the plants in the sphere ( table 1 ) for up to 6 days before they were allowed access to a blood source , in the form of a human volunteer sleeping in the hut . some plants like castorbean ( ricinus communis l. ) were flowering at the time of the experiment , and may have provided nectar sources . in cage experiments ( impoinvil et al . , in prep . )
we have observed a mean survival time of 7.0 0.2 days on this plant , which is comparable to mosquitoes given 6% glucose ( 8.7 0.2 days ) .
gambiae mosquitoes emerge from the pupal stage with a deficit not only in carbohydrates , but also lipid and protein , which usually is compensated for by consuming a ( small ) blood meal within the first few days of adult life , it is likely that mortality during the 6-day post - emergence period in the current trial was too high to have a good number of the 8090 females that emerged survive long enough to obtain their first blood meal . within 15 min of entering the hut at night ,
the volunteer noticed the sound of mosquitoes and subsequently felt mosquito bites on his exposed lower limbs .
this implies that females were receptive to host cues , entered the hut , probably through the eaves , and then successfully located and fed on the human host . at sunrise
, several engorged females were seen resting on the walls , indicating successful blood feeding and endophily ( indoor resting ) , which is typical for this species . following maturation of eggs ,
the second oviposition began during the night of day 21 , thus completing the life - cycle .
we continued to observe both immature and adult insects ( presumably mostly from the f1 generation ) until day 27 , when the experiment was terminated ( by refraining from entering the sphere for about 1 month ) .
the second experiment , in which we released 500 virgin females together with 1500 males demonstrated that mating does occur in a relatively small , semi - field system .
after the third night that a volunteer had slept in the hut , we observed eggs in the breeding sites
. the production of offspring , though , was low , and we only collected 40 pupae by the end of the trial period .
this may have been caused by heavy rainfall during three consecutive nights ( day 24 ) , which may have affected the survival of the adults and/or larvae or washed away the larvae from the breeding sites due to overflow .
since we observed few mosquitoes , we decided to conduct a human landing catch during two nights inside the hut , starting two nights after sleeping in the hut had ended .
nevertheless , the life - cycle was completed , as manifested by the harvested pupae , which were removed from the breeding sites to prevent emergence of the f1 generation which would have compromised interpretation of survival of the f0 generation .
the third experiment started by introducing 500 eggs into each of the breeding sites , whilst 1000 eggs ( from the same original batch ) were reared under laboratory conditions . in the laboratory , larvae developed at the same rate and
most reached maturity by day 10 , when the first pupae were observed ( fig .
this was similar for the breeding sites in the sphere , except that development was highly asynchronous , i.e. some larvae pupated by day 10 , whereas others took up to day 24 before pupation .
these times to pupation are similar to those observed in the first trial , but are again in contrast with other studies . on day 7
we counted all larvae and observed 887 in the insectary , as opposed to 652 in the sphere .
overall , the laboratory batch yielded 804 pupae , versus 495 from the breeding sites .
on the basis of these data , the average daily survival was 0.90 for the laboratory larvae , and 0.83 for the larvae in the sphere . with nearly half the larvae surviving to the adult stage , these results
contrast sharply with much higher mortalities ( up to 90% ) observed in the kisumu area and so tome ( charlwood , pers .
. the sex ratio of emerging adults in the laboratory was 2:3 , which translated into a female population in the sphere of 297 , on the assumption that no insects died during emergence .
on day 28 , after the release of eggs in the breeding sites , we observed that eggs had been laid by the f1 generation , but with only 6 and 3 eggs in the two breeding sites respectively .
cumulative percentage of pupation of eggs introduced in the two breeding sites inside the greenhouse ( ) or under insectary conditions ( ) .
our results have shown that by starting either at the post - blood feeding , pre - mating , or egg stage , a new generation of insects can be reared under these semi - field conditions , and that all life - history behaviours were successfully completed to a lesser or greater extent .
this therefore represents the first and promising step towards continuous maintenance of parasite - free an .
gambiae populations under semi - natural conditions that can be experimentally manipulated in studies of malaria vector ecology and transmission control .
russell and rao used a large outdoor cage , based on a design by hackett and bates , to study swarming and oviposition behaviour of an .
culicifacies giles in india , and showed that such systems can be used to unravel aspects of the behavioural ecology of anophelines .
our study shows that such systems can now also be developed for studies on african malaria vectors in order to start filling the gaps in our understanding of the behavioural ecology of these insects .
first and foremost , it provides a suitable intermediate between laboratory - based studies addressing mosquito behaviour and ecology , and the field situation .
too often , conclusions are drawn from results obtained under laboratory conditions that necessitate speculation as to what may or may not happen in the field .
fixed climatic conditions , cage - experiments , olfactometers and windtunnels , in which the mosquito strains used have been laboratory - reared for sometimes decades , may readily distort behavioural and ecological phenomena .
here we have shown that , beyond introducing f1 generation malaria - free mosquitoes from wild populations , it may be possible to rear vectors in situ within a semi - natural system that may minimize such artefacts .
conversely , the advantage of using insectary - reared mosquitoes is in the level of control that may be exerted that would not otherwise be possible : experiments can be conducted all - year - round , with fixed numbers of insects , of known age and physiological status , in a malaria parasite - free environment under ambient climatic conditions .
this enables more direct inferences to be drawn from data analysis as compared to longitudinal field studies , because of constant conditions and simplified experimental design .
we have recently evaluated the efficacy of several plants traditionally used by the luo community as repellents in a similar semi - field set - up , and simple logistic regression , on data collected during four nights per plant , yielded significant results . within a year of nearly continuous experimentation
, the repellency of 8 plant species and 3 combinations thereof was evaluated through thermal expulsion or direct burning , and 9 species and 2 combinations thereof were tested in potted form .
such studies would have taken several years under field conditions , and would be limited to times when mosquito densities would have been sufficiently high to permit meaningful experiments .
gambiae maintained on a variety of diets ( blood or sugar alone , or a combination of both ) and revealed similar results to those obtained under laboratory conditions .
within one year of starting studies on the behaviour of mosquitoes around bednets in a semi - field setup , we transformed a regular conical bednet into a trap that may catch up to 70% of the females released .
recent field evaluation of this trap shows it to be a promising replacement for the human landing catch ( mathenge et al .
, in preparation . ) . with the trap now being considered for commercial manufacturing ( it took a mere two years to reach this stage ) ,
this would have been impossible without the availability of a semi - field set - up in which continuous experimentation ensured rapid progress towards product development .
even though our system resembles more closely the field situation , it remains to be ascertained to what extent .
our current study was mainly qualitative in design and focused on life - cycle completion .
for instance , observation of eggs in the breeding sites in the morning of day 22 during the first trial implies that these originated from females that fed once on day 19 , as those that fed on day 17 should have laid before .
however , it is likely that these females fed twice , on day 17 and day 19 , and should be classified as pre - gravids , before fully maturing a batch of eggs .
furthermore , in the absence of a human host , mosquitoes survived up to six days after emergence , confirming field results that feeding on plant sugars does occur and may be an important feature of the life - cycle in this species ( foster and knols , unpublished data ) .
obviously , there are limitations associated with these studies . some phenomena , like dispersal ,
there may be other , yet unknown , factors that affect the behavioural ecology of the insects in such systems . or , as bates wrote , following his outdoor cage studies in albania : " one still can not be sure that the reactions of the mosquito are ' natural ' because there is always the barrier of wire liable to be encountered on extended flights ; and when the flight of a mosquito has been interrupted by this wire barrier its further activity may be definitely unnatural " .
rightly so , and even though we did not observe any obvious distorted behaviours , it is imperative that findings from semi - field studies be verified under natural outdoor conditions .
additional studies in which the release and performance of field - collected , blood - fed mosquitoes in the sphere is compared with that of laboratory specimens in terms of egg - recovery , developmental periods and important behavioural characteristics ( like swarming ) will provide further insight to what extent such systems mimic the natural anopheles environment and colony adaptation impairs natural behaviours . nevertheless , since bates ' days , advances in science merit a renewed impetus towards semi - field studies in contained near - natural environments , particularly with respect to transgenic mosquitoes .
fitness evaluations of engineered strains of vectors are mandatory for transformation technology to become an established disease control tool in africa . perhaps this alone , is ample justification for more intensive sphere studies , hopefully not only in kenya , but also in other african countries likely to be involved in this endeavour .
studies on gene flow , mating behaviour and reproductive fitness , combined with studies on the effects of laboratory maintenance on the genetic make - up of transformed strains to be released , can be conducted in semi - field systems .
such systems , particularly when used to study genetically - engineered mosquitoes will require more advanced containment levels than the system described here . guidelines for facility location , physical and biological containment , safety practices and calamity control need to be developed and adapted from existing arthropod containment guidelines .
there are several good reasons to further such studies in disease - endemic settings . under such conditions it will be possible to transform offspring from wild mosquitoes , conduct experiments under local ambient climatic conditions and evaluate transgene spread and fixation in offspring from field - collected gravid females that emerge in a semi - field setup .
last , but not least , it will enable scientists from developing countries to become more directly involved in evaluating the potential use and application of transgenic mosquitoes for future malarial disease control .
the introduction of blood - fed females into the greenhouse resulted in the presence of eggs in the breeding sites on day 3 ( 2.5 days after release ) , and eggs continued to be observed in the sites until day 7 ( fig .
3 ) . larvae ( from l1 to l4 stage ) were seen feeding at the water surface until day 23 , when the last l4 larva pupated .
the first five pupae were seen in the breeding sites in the evening of day 10 , meaning that the variation in maturation time from egg to pupa was 720 days . in spite of having conditions with higher larval density and smaller water surface area , gimnig et al . recorded much reduced periods to pupation , from 5 to 12 days . in total , 57 pupae were counted in the breeding site 3.8 m in front of the hut and 130 in the site 1.1 m behind it , and on average they harboured only 0.08 and 0.18 larva / cm , respectively .
these densities are lower than those observed in natural habitats , and given the fact that we observed algal growth , considered important for larval growth , it seems that the prolonged time to pupation in this trial may be attributed to the relatively small range over which temperatures fluctuate .
alternatively , re - introducing mosquitoes that had been maintained under laboratory conditions for several years in a more natural setting may have caused these effects , and poor adaptation to these conditions may have stunted their development .
completion of the anopheles gambiae life - cycle in the greenhouse over a 27-day period .
blood - fed females were released on day 1 , and arrows show time periods during which the various developmental stages were observed .
the first adults were seen inside the hut on day 11 , and continued to be present until the end of the experiment ( day 27 ) .
starting in the morning of day 22 , we observed new eggs in the breeding sites and subsequent larval development . from the above it
can be deduced that specific behaviours of the adult insects occurred during certain time periods ( fig .
oviposition activity took place twice during this trial , meaning that females survived until eggs were mature , that they successfully located a breeding site , accepted it for oviposition , and laid eggs .
other potential breeding sites , like the leaf axils of the banana trees in the sphere , were examined but were not found to harbour eggs , larvae or pupae . the period for reaching sexual maturity for
males may be at least one day and for females up to 60 hrs , so mating of the f1 generation may not have taken place until dusk on day 14 . in spite of regular observations during dusk , we did not see any swarming activity typically associated with mating in an .
this is a particularly interesting point , because in contrast with other settings ( e.g. ) , where mating swarms were frequently observed we failed to do so over a 3-year period in the mbita area as did charlwood ( pers.comm . ) who observed only one anopheline swarm during 4 years in the kilombero valley of tanzania , raising the question as to whether swarming is an obligate component of the an .
alternatively , maintenance of mosquitoes in laboratory cages for several years forced this strain to become stenogamous ( i.e. the ability to mate in small cages ) , and this adaptation may have interfered with its ability to swarm when introduced into the sphere . as newly emerged adults rarely survive for more than 48 hrs without the availability of an energy source , mosquitoes must have supplemented their energy reserves with carbohydrates from the plants in the sphere ( table 1 ) for up to 6 days before they were allowed access to a blood source , in the form of a human volunteer sleeping in the hut . some plants like castorbean ( ricinus communis l. ) were flowering at the time of the experiment , and may have provided nectar sources . in cage experiments ( impoinvil et al . , in prep . )
we have observed a mean survival time of 7.0 0.2 days on this plant , which is comparable to mosquitoes given 6% glucose ( 8.7 0.2 days ) .
gambiae mosquitoes emerge from the pupal stage with a deficit not only in carbohydrates , but also lipid and protein , which usually is compensated for by consuming a ( small ) blood meal within the first few days of adult life , it is likely that mortality during the 6-day post - emergence period in the current trial was too high to have a good number of the 8090 females that emerged survive long enough to obtain their first blood meal . within 15 min of entering the hut at night ,
the volunteer noticed the sound of mosquitoes and subsequently felt mosquito bites on his exposed lower limbs .
this implies that females were receptive to host cues , entered the hut , probably through the eaves , and then successfully located and fed on the human host . at sunrise
, several engorged females were seen resting on the walls , indicating successful blood feeding and endophily ( indoor resting ) , which is typical for this species . following maturation of eggs ,
the second oviposition began during the night of day 21 , thus completing the life - cycle .
we continued to observe both immature and adult insects ( presumably mostly from the f1 generation ) until day 27 , when the experiment was terminated ( by refraining from entering the sphere for about 1 month ) .
the second experiment , in which we released 500 virgin females together with 1500 males demonstrated that mating does occur in a relatively small , semi - field system .
after the third night that a volunteer had slept in the hut , we observed eggs in the breeding sites .
the production of offspring , though , was low , and we only collected 40 pupae by the end of the trial period .
this may have been caused by heavy rainfall during three consecutive nights ( day 24 ) , which may have affected the survival of the adults and/or larvae or washed away the larvae from the breeding sites due to overflow .
since we observed few mosquitoes , we decided to conduct a human landing catch during two nights inside the hut , starting two nights after sleeping in the hut had ended .
nevertheless , the life - cycle was completed , as manifested by the harvested pupae , which were removed from the breeding sites to prevent emergence of the f1 generation which would have compromised interpretation of survival of the f0 generation .
the third experiment started by introducing 500 eggs into each of the breeding sites , whilst 1000 eggs ( from the same original batch ) were reared under laboratory conditions . in the laboratory , larvae developed at the same rate and
most reached maturity by day 10 , when the first pupae were observed ( fig .
this was similar for the breeding sites in the sphere , except that development was highly asynchronous , i.e. some larvae pupated by day 10 , whereas others took up to day 24 before pupation .
these times to pupation are similar to those observed in the first trial , but are again in contrast with other studies . on day 7
we counted all larvae and observed 887 in the insectary , as opposed to 652 in the sphere .
overall , the laboratory batch yielded 804 pupae , versus 495 from the breeding sites .
on the basis of these data , the average daily survival was 0.90 for the laboratory larvae , and 0.83 for the larvae in the sphere . with nearly half the larvae surviving to the adult stage , these results contrast sharply with much higher mortalities ( up to 90% ) observed in the kisumu area and so tome ( charlwood , pers .
. the sex ratio of emerging adults in the laboratory was 2:3 , which translated into a female population in the sphere of 297 , on the assumption that no insects died during emergence . on day 28 , after the release of eggs in the breeding sites , we observed that eggs had been laid by the f1 generation , but with only 6 and 3 eggs in the two breeding sites respectively .
cumulative percentage of pupation of eggs introduced in the two breeding sites inside the greenhouse ( ) or under insectary conditions ( ) .
our results have shown that by starting either at the post - blood feeding , pre - mating , or egg stage , a new generation of insects can be reared under these semi - field conditions , and that all life - history behaviours were successfully completed to a lesser or greater extent .
this therefore represents the first and promising step towards continuous maintenance of parasite - free an .
gambiae populations under semi - natural conditions that can be experimentally manipulated in studies of malaria vector ecology and transmission control .
russell and rao used a large outdoor cage , based on a design by hackett and bates , to study swarming and oviposition behaviour of an .
culicifacies giles in india , and showed that such systems can be used to unravel aspects of the behavioural ecology of anophelines .
our study shows that such systems can now also be developed for studies on african malaria vectors in order to start filling the gaps in our understanding of the behavioural ecology of these insects .
first and foremost , it provides a suitable intermediate between laboratory - based studies addressing mosquito behaviour and ecology , and the field situation .
too often , conclusions are drawn from results obtained under laboratory conditions that necessitate speculation as to what may or may not happen in the field .
fixed climatic conditions , cage - experiments , olfactometers and windtunnels , in which the mosquito strains used have been laboratory - reared for sometimes decades , may readily distort behavioural and ecological phenomena .
here we have shown that , beyond introducing f1 generation malaria - free mosquitoes from wild populations , it may be possible to rear vectors in situ within a semi - natural system that may minimize such artefacts .
conversely , the advantage of using insectary - reared mosquitoes is in the level of control that may be exerted that would not otherwise be possible : experiments can be conducted all - year - round , with fixed numbers of insects , of known age and physiological status , in a malaria parasite - free environment under ambient climatic conditions .
this enables more direct inferences to be drawn from data analysis as compared to longitudinal field studies , because of constant conditions and simplified experimental design .
we have recently evaluated the efficacy of several plants traditionally used by the luo community as repellents in a similar semi - field set - up , and simple logistic regression , on data collected during four nights per plant , yielded significant results . within a year of nearly continuous experimentation , the repellency of 8 plant species and 3 combinations thereof was evaluated through thermal expulsion or direct burning , and 9 species and 2 combinations thereof were tested in potted form .
such studies would have taken several years under field conditions , and would be limited to times when mosquito densities would have been sufficiently high to permit meaningful experiments .
gambiae maintained on a variety of diets ( blood or sugar alone , or a combination of both ) and revealed similar results to those obtained under laboratory conditions .
within one year of starting studies on the behaviour of mosquitoes around bednets in a semi - field setup , we transformed a regular conical bednet into a trap that may catch up to 70% of the females released .
recent field evaluation of this trap shows it to be a promising replacement for the human landing catch ( mathenge et al .
with the trap now being considered for commercial manufacturing ( it took a mere two years to reach this stage ) , this would have been impossible without the availability of a semi - field set - up in which continuous experimentation ensured rapid progress towards product development .
even though our system resembles more closely the field situation , it remains to be ascertained to what extent .
our current study was mainly qualitative in design and focused on life - cycle completion .
for instance , observation of eggs in the breeding sites in the morning of day 22 during the first trial implies that these originated from females that fed once on day 19 , as those that fed on day 17 should have laid before .
however , it is likely that these females fed twice , on day 17 and day 19 , and should be classified as pre - gravids , before fully maturing a batch of eggs .
furthermore , in the absence of a human host , mosquitoes survived up to six days after emergence , confirming field results that feeding on plant sugars does occur and may be an important feature of the life - cycle in this species ( foster and knols , unpublished data ) . obviously , there are limitations associated with these studies
there may be other , yet unknown , factors that affect the behavioural ecology of the insects in such systems . or , as bates wrote , following his outdoor cage studies in albania
: " one still can not be sure that the reactions of the mosquito are ' natural ' because there is always the barrier of wire liable to be encountered on extended flights ; and when the flight of a mosquito has been interrupted by this wire barrier its further activity may be definitely unnatural " .
rightly so , and even though we did not observe any obvious distorted behaviours , it is imperative that findings from semi - field studies be verified under natural outdoor conditions .
additional studies in which the release and performance of field - collected , blood - fed mosquitoes in the sphere is compared with that of laboratory specimens in terms of egg - recovery , developmental periods and important behavioural characteristics ( like swarming ) will provide further insight to what extent such systems mimic the natural anopheles environment and colony adaptation impairs natural behaviours . nevertheless , since bates ' days , advances in science merit a renewed impetus towards semi - field studies in contained near - natural environments , particularly with respect to transgenic mosquitoes .
fitness evaluations of engineered strains of vectors are mandatory for transformation technology to become an established disease control tool in africa . perhaps this alone , is ample justification for more intensive sphere studies , hopefully not only in kenya , but also in other african countries likely to be involved in this endeavour .
studies on gene flow , mating behaviour and reproductive fitness , combined with studies on the effects of laboratory maintenance on the genetic make - up of transformed strains to be released , can be conducted in semi - field systems .
such systems , particularly when used to study genetically - engineered mosquitoes will require more advanced containment levels than the system described here . guidelines for facility location , physical and biological containment , safety practices and calamity control need to be developed and adapted from existing arthropod containment guidelines
. there are several good reasons to further such studies in disease - endemic settings . under such conditions it will be possible to transform offspring from wild mosquitoes , conduct experiments under local ambient climatic conditions and evaluate transgene spread and fixation in offspring from field - collected gravid females that emerge in a semi - field setup .
last , but not least , it will enable scientists from developing countries to become more directly involved in evaluating the potential use and application of transgenic mosquitoes for future malarial disease control .
bgjk conceived of the study , and developed the system and experiments together with bnn , emm and wrm .
jcb and gfk actively contributed to the interpretation of the findings and drafting of the final manuscript .
bgjk and emm are engaged in commercialising the mbita bednet trap , developed in semi - field systems similar in nature to that described in this article , in collaboration with the vestergaard frandsen group ( denmark ) .
bos of wageningen university and research centre ( the netherlands ) for assistance with plant nomenclature .
this research was supported by the national institutes of health , usa ( grant numbers u19 ai45511 , d43 tw01142 , d43 tw00920 ) .
emm and wrm receive financial support from the undp / world bank / who special programme for research and training in tropical diseases ( tdr ) under grants i d 980794 and 980692 respectively . | backgroundthe development and implementation of innovative vector control strategies for malaria control in africa requires in - depth ecological studies in contained semi - field environments .
this particularly applies to the development and release of genetically - engineered vectors that are refractory to plasmodium infection .
here we describe a modified greenhouse , designed to simulate a natural anopheles gambiae giles ecosystem , and the first successful trials to complete the life - cycle of this mosquito vector therein.methodswe constructed a local house , planted crops and created breeding sites to simulate the natural ecosystem of this vector in a screen - walled greenhouse , exposed to ambient climate conditions , in western kenya . using three different starting points for release ( blood - fed females , virgin females and males , or eggs ) , we allowed subsequent stages of the life - cycle to proceed under close observation until one cycle was completed.resultscompletion of the life - cycle was observed in all three trials , indicating that the major life - history behaviours ( mating , sugar feeding , oviposition and host seeking ) occurred successfully.conclusionthe system described can be used to study the behavioural ecology of laboratory - reared and wild mosquitoes , and lends itself to contained studies on the stability of transgenes , fitness effects and phenotypic characteristics of genetically - engineered disease vectors .
the extension of this approach , to enable continuous maintenance of successive and overlapping insect generations , should be prioritised .
semi - field systems represent a promising means to significantly enhance our understanding of the behavioural and evolutionary ecology of african malaria vectors and our ability to develop and evaluate innovative control strategies . with regard to genetically - modified mosquitoes , development of such systems
is an essential prerequisite to full field releases . | Background
Methods
Design
Mosquitoes
Life-cycle completion
Ethical considerations
Results and Discussion
Microclimate
Life-cycle completion
Blood-fed females
Males and virgin females
Eggs
Authors contributions
Competing interests
Acknowledgements |
causality assessment ( ca ) , is a method of evaluation used in pharmacovigilance to find out the relationship between drugs exposed and reported adverse drug reactions ( adr ) .
it includes , finding the temporal relationship between drugs and reported adr , dechallenge , rechallenge , clinical and pathological characteristics of the events .
it is difficult for the practitioner with careful monitoring to identify the drugs causing adr .
in such a condition the withdrawal of drugs one at a time and evaluating the reaction of dechallenge has become essential .
dechallenge is a response observed in a patient such as reduction or disappearance of adr after withdrawal of a drug .
there are two types of dechallenge namely positive dechallenge which resolves with the withdrawal of drug and the negative dechallenge which follows a course of its own .
decision on the withdrawal of drug has been considered from the point of adr underlying the disease .
a typical procedure has to be followed before attempting rechallenge , with an understanding of risk involved for the patient .
so the prescribers and the patients may not come forward for the procedures involved except on a few occasions .
the prescribers too prefer to adopt dechallenge rather than rechallenge . detecting adverse drug reactions and dechallenge
data mining is a kind of statistical approach for discovering useful patterns from enormous amount of data .
it contains algorithms to find out the pattern by means of various approaches like classification , prediction , clustering and association .
data - mining algorithm called multi - item gamma position shrinker is now used for signaling potential adrs by food and drug administration ( fda ) in us .
the naive bayes ( nb ) a statistical classifier predicts class membership probabilities widely used by researchers in data mining for classification . it is assumed that all the variables contributing toward classification are mutually independent .
medical dictionary for regulatory activities ( meddra ) , an international medical terminology developed under the auspices of the international conference of harmonization of technical requirements for registration of pharmaceuticals for human use ( ich ) is a controlled medical vocabulary for describing adverse events with five levels : the coarsest is system organ class ( soc ) , followed by high level group term ( hlgt ) , higher level term ( hlt ) , preferred term ( pt ) , and lowest level term ( llt ) , the finest grained description .
the duplicate reports were deleted in accordance to fda 's recommendation of adopting in recent case number as described in one of the files asc - nts.doc from the website of the fda .
fda had stored diseases category at preferred terms ( pt ) level . among the five levels of adverse events hierarchy of meddra
, soc level was used to classify the diseases category by referring to cancer therapy evaluation program simplified disease classification v4.0 ( meddra v 12.0 ) .
researchers suggested that it might be more advantageous to perform data mining , using a coarser grained adverse event representation soc than pt level .
the data were loaded from fda 's text file to oracle database using extract , transform and load ( etl ) tools .
records with soc as gastrointestinal , renal and urinary , metabolism and nutrition disorders were considered for dechallenge classification .
the attributes considered to evaluate dechallenge were the diseases categories denoted as system organ class ( soc ) in meddra , drug with valid trade and verbatim name represented by code 1 and 2 by fda , outcoming like life - threatening ( lt ) , death ( de ) , congenital anomaly ( ca ) , hospitalization - initial or prolonged ( ho ) , disability ( ds ) , required intervention ( ri ) to prevent permanent impairment had been considered for determining the occurrence of dechallenge .
the process of determining suitable algorithm for detecting dechallenge was accomplished by comparing nb and nb .
the performance of data mining algorithm was estimated by the parameters like percentage of accuracy , error , precision and receiver operating characteristic ( roc ) curve .
all the parameters were depicted by 2 2 confusion matrixes , containing the total number of true positive ( tp ) , true negative ( tn ) , false positive ( fp ) and false negative ( fn ) , where positive referred to identified set and negative to rejected set .
accuracy , precision and error were calculated by formula 1 , 2 and 3 as follows : roc curve was used to convey the graphical representation of perfect , liberal , random and conservative performance of an algorithm .
statistical data mining techniques had been implemented in the field of post - marketing surveillance .
safety signal detection problems in pharmacovigilance were examined by roy and jeffrey et al . , statistical data sources and data mining methods used in safety signal were studied by atsuko and manfred et al . , liang and rongzhan et al .
corani and zaffalon proposed an extension of nb named as naive credal classifier to issue reliable classifications for a domain with high uncertain information .
zhang et al . , proposed a novel model called hidden naive bayes to avoid computational complexity . for data mining model , each patient
the disease category was denoted in soc level , by mapping the pt of fda with meddra pt using extensible markup language ( xml ) mapping .
nb theorem given in formula 4 had been used to calculate the probability of an outcome .
the class label attribute dechallenge had two distinct values ( yes , no ) represented by hypothesis ( h ) .
p(h / x ) is the posterior probability where hypothesis ( h ) represents the presence of dechallenge with x as known disease category , drug code and outcome .
p ( x / h ) is the posterior probability of x on the subject of h. p ( h ) is the prior probability of h regardless of disease category , drug code and outcome .
p(x ) is the prior probability of x. for calculating the prior probability p ( x ) , dechallenge record sets with
then the posterior probability was calculated based on outcome , disease category and drug code .
the data set of 2011 and 2012 records contained the constraints mentioned for the failure of naive bayes classifier . to overcome this , nb algorithm proposed by balamurugan et al . , was applied in the present study as detailed below .
this algorithm starts with the influence factor as the first step to determine the dependability of an attribute value on the class attribute .
influence factor was calculated for the attributes drug code , disease category and outcome on the class label dechallenge .
where i(x / ci)=influence factor n(x\ci ) = number of records in which attribute value x had the class label ci and n(ci)=total number of records in which the class label were ci .
statistical data mining techniques had been implemented in the field of post - marketing surveillance .
safety signal detection problems in pharmacovigilance were examined by roy and jeffrey et al . , statistical data sources and data mining methods used in safety signal were studied by atsuko and manfred et al . , liang and rongzhan et al .
corani and zaffalon proposed an extension of nb named as naive credal classifier to issue reliable classifications for a domain with high uncertain information .
zhang et al . , proposed a novel model called hidden naive bayes to avoid computational complexity . for data mining model , each patient
the disease category was denoted in soc level , by mapping the pt of fda with meddra pt using extensible markup language ( xml ) mapping . the fundamental assumption to attribute independence
nb theorem given in formula 4 had been used to calculate the probability of an outcome .
the class label attribute dechallenge had two distinct values ( yes , no ) represented by hypothesis ( h ) .
p(h / x ) is the posterior probability where hypothesis ( h ) represents the presence of dechallenge with x as known disease category , drug code and outcome .
p ( x / h ) is the posterior probability of x on the subject of h. p ( h ) is the prior probability of h regardless of disease category , drug code and outcome .
p(x ) is the prior probability of x. for calculating the prior probability p ( x ) , dechallenge record sets with
then the posterior probability was calculated based on outcome , disease category and drug code .
the data set of 2011 and 2012 records contained the constraints mentioned for the failure of naive bayes classifier . to overcome this , nb algorithm proposed by balamurugan et al . , was applied in the present study as detailed below .
this algorithm starts with the influence factor as the first step to determine the dependability of an attribute value on the class attribute .
influence factor was calculated for the attributes drug code , disease category and outcome on the class label dechallenge .
/ ci)=influence factor n(x\ci ) = number of records in which attribute value x had the class label ci and n(ci)=total number of records in which the class label were ci .
statistical data mining techniques had been implemented in the field of post - marketing surveillance .
safety signal detection problems in pharmacovigilance were examined by roy and jeffrey et al . , statistical data sources and data mining methods used in safety signal were studied by atsuko and manfred et al . , liang and rongzhan et al .
corani and zaffalon proposed an extension of nb named as naive credal classifier to issue reliable classifications for a domain with high uncertain information .
zhang et al . , proposed a novel model called hidden naive bayes to avoid computational complexity .
the other data were outcome of drug and disease category . drug classified by fda as 1 for valid trade and 2 for verbatim name .
the disease category was denoted in soc level , by mapping the pt of fda with meddra pt using extensible markup language ( xml ) mapping .
nb theorem given in formula 4 had been used to calculate the probability of an outcome .
the class label attribute dechallenge had two distinct values ( yes , no ) represented by hypothesis ( h ) .
p(h / x ) is the posterior probability where hypothesis ( h ) represents the presence of dechallenge with x as known disease category , drug code and outcome .
p ( x / h ) is the posterior probability of x on the subject of h. p ( h ) is the prior probability of h regardless of disease category , drug code and outcome .
p(x ) is the prior probability of x. for calculating the prior probability p ( x ) , dechallenge record sets with
then the posterior probability was calculated based on outcome , disease category and drug code .
the data set of 2011 and 2012 records contained the constraints mentioned for the failure of naive bayes classifier . to overcome this , nb algorithm proposed by balamurugan et al . , was applied in the present study as detailed below .
this algorithm starts with the influence factor as the first step to determine the dependability of an attribute value on the class attribute .
influence factor was calculated for the attributes drug code , disease category and outcome on the class label dechallenge .
where i(x / ci)=influence factor n(x\ci ) = number of records in which attribute value x had the class label ci and n(ci)=total number of records in which the class label were ci .
it is observed from table 1 , influence factor is high for outcomes such as ho and lt , drug code with code 1 and disease category such as gastrointestinal disorder .
yes for combinations like gastrointestinal disorder with outcome as ho and lt and for drugs with code 1 . hence classifying the dechallenge for unknown records with same combinations of attributes can be predicted as
influence factor analysis of outcome , disease category , and drug code with dechallenge performance analysis of nb and nb provided in table 2 , where the average accuracy of nb is 90.11 and nb is 70.25 , average error of nb is 19.8 percent higher than nb , and precision of nb is 7.4 percent higher than nb . it is observed from experimental result , nb performs well in case of attributes with categorical values and zero probability issue . in the roc graph shown in figure 1 ,
although nb fits in the category of liberal performance with true positive rate as ( .7 , .8 , .9 , .9 ) , there is also substantial number of false positive rate ( .6 , .7 , .6 , .5 ) ; whereas nb fits in perfect performance with true positive rate as ( .9 , .9 , .9 , .9 ) , and minimal false positive rate as ( .2 , .8 , .0 , 0 ) .
comparison of performance analysis of error , precision and accuracy of nb and nb receiver operating characteristic curve for improved nave bayes and naive bayes
the fda uses data mining to screen the aers database using bayesian protocol for the presence of disproportionality in large adverse event - drug product pairs , but the data must be evaluated to determine causality reviews like dechallenge .
the performance of any data - mining algorithm depends on the type of attributes and its application .
a common means of identifying the association between drug and disease in pharmacovigilance is through disproportionality analysis .
this produces the results based on 2 2 tables as there are relevant drug and adr combination .
hence for large amount of data , this method will produce more number of tables which reduces the effectiveness of the approach .
several studies reported the need of data mining algorithms to review the data to make authoritative conclusion .
many studies reported the usage of mining algorithms like proportional reporting ratio , multi - item gamma - poisson shrinker .
further investigation of statistical methods to analyze large amount of data is essential to improve the effectiveness of pharmacovigilance activities .
hence in this study the data mining algorithms like nb and nb for determining the performance of algorithms in enormous data for detecting dechallenge have been investigated . among the 26 soc disease categories ,
the results presented here are based on 3 socs such as gastrointestinal , metabolism and nutrition , renal and urinary disorders . when nb is used to detect the dechallenge ,
the posterior probability is zero for records with outcome as ca and disease category as gastrointestinal disorder .
hence 72 records of the year 2011 fourth quarter are classified as unknown by nb algorithm .
the algorithm fails when the probability of a particular outcome or disease is uniformly distributed .
nb resolved zero probability issue by determining attributes with high influence factor and thus reducing the noise present in data for effective detection of dechallenge .
nb can be applied to any dataset which suffers from zero probability exertion . from the experimental analysis ,
it is clear that nb can be used for large data set in detecting causality reviews . for the fda
record sets , nb produced higher accuracy than nb and detected the dechallenge value as yes for drugs with code 1 and gastrointestinal disorder with outcome as ho and lt .
influence factor analysis in nb proved the usage of this algorithm in pharmacovigilance for predicting unknown samples .
most data available in fda and world health organisation ( who ) have neither brought in health science education , nor trained to utilise for patient care purpose .
post - marketing surveillance techniques like detecting dechallenge will help the practitioners and prescribers to gain knowledge about drugs with various reactions .
the outcome of the classification algorithms show that nb outperformed nb in traditional interesting measures like accuracy and minimal error in classifying dechallenge . | aim : dechallenge is a response observed for the reduction or disappearance of adverse drug reactions ( adr ) on withdrawal of a drug from a patient . currently available algorithms to detect dechallenge have limitations .
hence , there is a need to compare available new methods . to detect dechallenge in spontaneous reporting systems , data - mining algorithms like naive bayes and improved
naive bayes were applied for comparing the performance of the algorithms in terms of accuracy and error .
analyzing the factors of dechallenge like outcome and disease category will help medical practitioners and pharmaceutical industries to determine the reasons for dechallenge in order to take essential steps toward drug safety.materials and methods : adverse drug reactions of the year 2011 and 2012 were downloaded from the united states food and drug administration 's database.results:the outcome of classification algorithms showed that improved naive bayes algorithm outperformed naive bayes with accuracy of 90.11% and error of 9.8% in detecting the dechallenge.conclusion:detecting dechallenge for unknown samples are essential for proper prescription .
to overcome the issues exposed by naive bayes algorithm , improved naive bayes algorithm can be used to detect dechallenge in terms of higher accuracy and minimal error . | Introduction
Materials and Methods
None
Related Works
Data Mining Model
The Algorithms Used
Improved Naive Bayes
Results
Discussion
Conclusions |
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"to report a case of visually significant band keratopathy associated with ocular inflammation and s(...TRUNCATED) | " purposeto report a case of visually significant band keratopathy associated with ocular inflammati(...TRUNCATED) | Purpose
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Case report
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"unilateral vestibular hypofunction ( uvh ) is a vestibular disorder in which a total or \n partial (...TRUNCATED) | " [ purpose ] this study investigated to determine whether the sideways stepping test ( sst ) \n is (...TRUNCATED) | INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION |
"the most radical example is natural - orifice transluminal endoscopic surgery ( notes ) , which int(...TRUNCATED) | " background and objectives : natural - orifice approaches for nephrectomy have included access via (...TRUNCATED) | INTRODUCTION
METHODS
RESULTS
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"cervical spondylotic myelopathy ( csm ) and cervical spondylotic radiculopathy ( csr ) are classica(...TRUNCATED) | " \n background . the authors describe a lateral approach to the cervical spine for the management o(...TRUNCATED) | "1. Introduction\n2. Technique Indication\n3. Inclusion-Exclusion Criteria\n4. Surgical Technique\n5(...TRUNCATED) |
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