Jpn. J. Infect. Dis., 53, 107‑Ilo, 2000

Original Article

The Impact of Houslng Structures on Filarial Infection
Kalpana Baruah* and Raj Narayan Rail

Medical Entomology and Vector Control Division, National Institute ofCommunicable Diseases,
22‑Shamnath Marg, Delhi ll 0054 andJRegional Filaria Training and Resewch Centre, National Institute ofCommunicable Diseases, Varanasi Branch,
B‑20/44, Bhelupura, Varanasi 221 001, Uttar Pradesh, India(Received December 13, 1999. Accepted May 12, 2000)
SUMMARY: A study was undertaken to correlate the impact ofhouslng and pattems of house construction onthe vector densityand transmission of filaria among the inhabitants of these houses. Three different types ofhouses in ecologically similar hamlets of Hariharpur village in Varanasi were selected for determining the densityof Culex quinquefasciatus･ the vector of Wuchereria bancnofti and its infectivity･ The maximum pe.r man hourdensity of the vector was recorded during March (31.66, 40.33 and 41.33) while mlnlmum Was
recorded during June (I.3, 2.6 and 0.33) in all the threetypes of houses. Infection rate in the vectors collectedfrom poorly constructed houses was observed during April, May, October and January of the followlng year,
whereas in moderately constructed houses, infection was observed only in September and in the wellconstructed houses dissection results did not reveal any infection during the months of the study. Infectivity rate

was observed to be 10･0% in moderately constructed houses (group B) during the month of September and
14･2% in poorly constructed houPes (group C) during the month ofOctober･ Parasitological observations Ofthe

population showed a 12.2% mlCrOfilaria (mq rate and 6.7% disease rate among the residents of poorly
constructed houses, 5.8% mf rate and 2.9% disease rate among residents of moderately constructed houses.
Among residents of well built houses (Group A), none were found to be positive with mf, but disease rate wasobserved to be 2.7%. Throughout the year the relative humidity was observed to be higher in the poorly
constructed houses and ambient temperatures were found to be lower during the summer but higher during thewinter than to those of the better constructed houses. The study made evident that the construction of houses
plays an important role in the vector's resting preference, leading to a higher density in poorly constructedhouses, thereby increasing the possibility of infection within them, and thus maintaining a higher potential forfilarial transmission among its inhabitants.

Considering the encouraglng findings of the above study,

INTRODUC TION

as well as observations made by various authors in other parts

TYle findings ofa longitudinal study for esdmatingthe vectorof the globe, the present study was undertaken to assess thedensity of Culex.quinquefasciat?∫ showed the vector ofrestlng Preference of this vector in houses constructed bybancroRian filariasIS in Varanasi projected high‑vector density

various means, by studying its denslty, infection and infec‑

in houslng COnditions which were unhygienic due to improper

tivityrates. The impact of the above factors was assessed bylighting and ventilation and suggested conditions which wouldundertaking a night blood survey of the inhabitants or theidentified classes of houses. An effort has been made in thisbe ideally conducive f♭r resting this vector species (1,2).

Varanasi is a city situated on the bank of the river Ganges

paper to correlate the probability of filarial infection byassesslng entomological and parasitological parameters.

and is known for its high rllaria endemicity(2). It has been
observed thatthe disease rate is higher among the inhabitantsof such houses. These findings authenticate the congenial

h4ATERIALS AND METHODS

conditions for the preferred resting of Cx. quinquefasciatus;
inhabitants of unhygienic houses were more exposed toThe study was camied out between March 1 994 and February

infection with Wuchereria bancrlOfti as compared to those who

1995 in Hariharpur village orVaranasi which has a popula‑

livedinthe properly designed houses withadequate ventilation

tion of approximately 2,000 and depends on agrlCulture forand lighting. This observation was supported by the results

its livelihood. The village is composed ofsmall hamlets. Forof the dissection. Higher Cx. quinquefasciatus infection andthe study, three types of houses from ecologlCally similar

infectivity rate were collected &om poorly constructed houses

backgrounds were selected and co°ed as groups A, B and Cthan from well constructed ones.
favorable and congenial resting place for the vector of(Table 1). Group A houses were better constmcted, withconcrete wallsand roofsand cement floors, withWell ventilatedrooms and proper lighting. Group B houses had unplasteredbancroftian filariasis as compared to houses with tiled roofs

brick walls, tiled roofs and mud floors with inadequate light

Reports show that poor housing withdim lighting is a moreand ceilings and stone or brick walls or houses with tiledand ventilation. Group C houses were poorly constructed,roofs and cement floors resulting ln more intense transmission

with mud‑plastered walls, tiled roofs and mud‑plasteredin the poorly constructed houses (3‑5).

floors, With inadequate ventilation and light. Twelve houses
from each group were selected for the study.

*Corresponding author: Tel/Fax: +91‑1 113912963

Adult house‑resting mosqultOeS Were COllected fortnightly

107

Table I. Classification of various types of houses

Code 夫ﾆﾂ

Roof 杷ﾆ"GroupA WellConstmcted

GroupB

Moderate

VﾖV蹌

&GroupC Poor 蕃VBVentilation andLightingCementVﾖV蹌

W&6V蹤"VﾆAdequaterⅠnadequateRｲTiledVﾖV蹌

ﾆ7FW&VB

Tiled 蕃VBF柳笋

Verypoor 鼎ゅ'Percent inhabitants of thevillage, residing ln Particular group of houses

mosqultOeS COllection 9.33, 13.1 8 and 13. 19. The 95% confi‑

during early moming hours (6:00 ‑9:00 a.m.)from every housein each group. Collections from every house in the study weredence limit for pmhd in well constructed or group A houses

made f♭r 15 min with aspirator tubes (suction tubes) as per

was found to be 6 to 30; in moderately constructed, or group

World Health Organization (WHO) guidelines (6) and kept

B houses, ll to 41; and in poorly constructed, or group C

separately. Mosquitoes were identified and per man hourhouses, 10 to 42. The arithmetic mean of group C was testeddensitybmhd) was calculated･ Females of the vFctOr Species

for slgnificance against that ofAand B:the 't'valuefor C vs. ACx. quinquefasciatus were dissected to determlne infection

was calculated to be 0.86 which was not significant; similarly

andinfectivity rate, if any. The mid‑gut blood content of eachthe ̀t'value f♭r C vs. B was calculated to be 0.13, which ismosqultO Was COllected on filter paper for serological analyses,

also not slgnificant.

and through the use ofgel difhsion method, the host predilec‑

Comparative analyses of the pmhd of group Cwith that oftion of the vector was determined (7). The comparative datagroups A and B did not show any slgnificant differences. Chi
square values obtained for group C with A were x2= 5.577

generated from each of the three groups was subjected tostatistical analyses. Temperatureand humidityWere recorded(P < 0.5) on ll degrees offreedom; likewise with group B

inside each house at the time of collection.

they were x2= 5.338 (P< 0.5) on 1 1 degrees offreedom. ThisA night blood survey was camied out during the month ofshows that the month‑Wise distribution of pmhd also not

April I 994. Finger‑prick blood smears were collected on glassdifferent between the groups.
Dissection of vectors from each group (Table 2) revealed
that in group C houses infections were observed during April,slides between the hours of 9:00 and I I:00 p.m. Effort wasmade to collect blood slides kom the inhabitants of each group

ofhouses･ These slides were stained with J･S･B (JasYant SinghMay, October and January of the followlng year, While inand Bhattacharjee) stain and ex?mined under a mlCrOSCOPe

group B houses 10.0% infection was observed only during

for the presence of microfilariae ln accordance with NationalFilaria Control Program (NFCP) guidelines (9).
TTle indicesand parameters used in the studyare as follows:

the month of September. However, no infection was found ingroup A houses at any time throughout the year. TTLe infectivity
rate was found to be 10.0% in the month of September ingroup a houses and 14.2% in group C houses in the mon血ofpmhd =No. of mosquitoes collected

October. The mid‑gut blood of2375 (halffed,fullfedand Semi

Time in hours spent on mosquito collectiongravid) females was subjected to serological analyses by gel
di瓜lSion method, which revealedthat 92.0% (2 1 85 out of2375)

No. offemales in the vector found tocontain developlngand developed

Vector infection rate (%) =of the vector Cx. quinquefagcidhLS COllected危d on humanblood.

Results of the night blood survey presented in Table 3 show

stages of parasite (stage I, II and III)×100

No. offemale dissected in the vector

that, out ofa total of 194 blood smears collected, 15 were

found to be positive for mf(mf rate 7.7%) and 9 0fthese( Micromaria (mf) stage is not included in the enumerator of vector

positive blood smears had disease manifestations. The mfrateinfection.)

was 5.8 and 12.2% in group B and C houses respectively; noNo. Offemales in the vector found topositive blood smears were found in group A houses. The
disease rate was found to be 2.7, 2.9 and 6.7 in group A, B

contain developed stages of parasite

Vector infectivityrate (%) =Mfrate (%) =(stage III)

×100

and C houses respectively. Temperature and relative humidity

No. offemale dissected in the vector

data inside the houses of each group at the time of collection

Totalno. of persons found to harbor mf
×100

are presented in Table 4. The room temperature in group C

Totalno. of persons examinedhouses was observed to be 0.5 to 1.OoC lower during warm

No. of persons showing slgnS and symptoms

Disease rate (%) =months (March to September) than that of group A and Bof filaria disease manifestation

houses while during cooler months (October to February), it

No. of persons examined for filaria disease

was 0.5 to 1.OoC higher. Similarly, the relative humiditywas
observed to be 5.0 to 10.0% higheringroup C houses.Analysesof the meteorologlCal data for the studyperiod revealed thatRESUIXS

the 95% confidence limit of average room temperature wasMonth by month pmhd of Cx. quinquefasciatus, along withll to39ingroupA, ll to 39 ingroupB and 12 也 37 ingroupthe results of each group's dissection,are presented in Table 2.

0.33 during June, in group A, B and C houses respectively.

C houses. Similarly, the 95% confidence limit of relativehumidity was 19 to 78 ingroupA, 20 to 81 in group B and26
to 90ingroup C houses. However, the 5 to lO% difference inthe relative humidityin group C houses could not be proven

The aritlmetic mean for group A, B and C houses was foundto be statistically slgnificant for the present sample.

A maximum pmhd of3 1.66, 40.33 and 41.33 were obseⅣed
during the mon仇ofMarch and a minimum of 1.3, 2.6 andto be ll.95, 15.28 and 15.98, with a standard deviation of108

Table 2. Manhour density, infection and infectivity rate of Culex quz'nquefasciatus among three groups of houses
GroupA
Moれ血s 彦F/Year 稗蝟ﾅ6Wﾆ踉踐b
9 ﾆD

U2

Man 薄詛V7F柳Infectivity 彦

hour density

FRMar94
S

都

Jul鼎B

Åug

4.00

Octb

2.6Nov

都B
B
都"田"

SD
95%

00"

02.60

07.33

0002ll.95

06.00

B013.30B

17.30

R014.212.66

塔008.33

都b000

7.66

5.30rate02bFR0b19.33

鉄015.28

釘絣19.1000015.98

13.18

澱ﾓ341.33

鼎b

Infectivity

hour density

0.33

017.20Man 薄詛V7F柳

ﾆﾆV7FVB

41.13"15.000mean

015.30涛610.00

8.33

涛"ﾆ踉踐bW2

C05.30

鉄17.3

FV友b

5.00

09.33
C.し.

24.33

鼎B

7Cr3.33

12.0

metlC

rate 蒙00010.3

Infectivity 彦FR

40.33

012.3

Dec

Man 薄詛V7F柳

39.33

b5.33

B

Ar坤一0

劔GroupC

hour density

C"

Cb7.33Sept

ﾆ踉踐b9 ﾆW23b01.3"Jan95013.00

唐F

ﾒ胯ﾅ6W

026.33

JunFebrate

31.66

AprMay劔GroupB

13.19

免ﾂﾓC

ﾓC"

X2 (C vs. A)=5.577 0n ll degrees of舟eedom (P < 0.5); (C vs. B)=5.338 0n ll degrees offreedom (P < 0.5), C･L･: confidence limit･

DISCUSSION

Table 3. Results orthe night blood suⅣey

GroupA 背&W"

Totalno.ofblood smearscollected

Positivefbr

microfilariaGroupC 彦b68 涛辻4FHouse construction and ambient eco‑climatic conditionsﾂ

influence vector densityand man/ mosquito contact, which

194

免ﾂin tum determine theintensity of disease transmission. A longterm study in Tanzania satisfactorily demonstrated that modifi‑

15

cation of houses may supplement other control strategies forfilariasis (8).

Microfilariarate(%) 辻
Disease

5.8"

manifestation

27.7
澱Parasitological observations in the present study clearly

indicate a higher prevalence of mfrate (12.2%) among the9inhabitants of poorly constructed houses than that among theDiseaserate(%)

縒2.9 澱縒

inhabitants of moderately constructed houses (5.8%) and nil
inwell constructed houses. In a study camied out at the sea port

4.6

Table 4. Average temperatureand relative humidity recorded atthetime of collection
between 6:00 and 9:00 a.m.

Month/Year

背&W

TempoCMarchノ94

April

May"纈

b縒

R縒

June

縒

August偵纈November
DecemberJanuary/95

February

Arithmetic mean

途

95%C.し.

B

35.9

B絣

43.2

20.8
絣

偵

60.7

偵

ゅ

R

59.6

50.2
R

(Mean土2SD)=

49.07

途

免ﾂﾓ3

ゅR

46.5

b絣

64.5

53.8
"56.2b纈

65.7

61.5

b69.4

r

58.9

R貳ﾂ50.69

15.18

19‑78

6s3

lO980.2

52.0"

RH: relative humidity, C.L.: confidence limit

30.0
85.0

69.9

ゆ60.0

14.69

縒

72.0

偵

49.7

R經r

50.0

"

48.0R

絣R縒

57.4

b縒

43.9

澱20‑81

W３

41.9

58.5

絣

背&R縒

45.3

R縒

"

TempOC

35.3

67.8

偵

W

３"b絣

70.2

September

SD

42.0

20.3

July

October

TempoC

34.6

35.0

"纈

背&

３R

2

58.23

15.96
"ﾓ3r

26‑90

2

ofAlleppy in Kerala, India, showed that 41. 1% of the total

Institute of Communicable Diseases (N.I.CD.) for his

mf carriers were inhabitants of thatched houses and onlyencouragement and the Joint Director of the Division ofHelminthology, N.I.C.D., Delhi, for providing facilities for

22.6% were inhabitants of tiled houses (5). Reports from Indo‑nesia showed higher mfand disease ratesinPoorly constructed

the study. The authors are also thankful to Dr. M. A.

houses with partial brick/wooden or bamboo‑Woven walls,Devadathan, Deputy Director, N.I.C.D., for the statisticalmud or partly cement floors, and unscreened windows which

guidance provided in prepanng this manuscrlpt. The teclmical

were inadequately lit or poorly ventilated (3). In Mambrui,assistance provided by the staffs ofRFT & RC in Varanasi isKenya, transmission was observed to be more intense, With

duly acknowledged.

higher mf rates and heavy mf densities, along with enlarged

lymplmodesinthe grolnS Ofpeople inhabiting poorly conshcted

REFERENCE S

houses (4).

Man‑hour densityofthis vector in the present study showed

1. Baruah, K., Shanna, R. S., Dey, K. P.andRai, R. N. (1995):

similar seasonal variations to those fわund in earlier studies

Bio ecology of filariasis vector Culex quinquefasciatus,(1). Dissection of vectors in group B houses revealed a 10.0%
infectionand infectivityrate during the month of September.

in Varanasi, India. Mosquito‑Bomモ Disease Bull., 12,This high rate may be due to the low sample size: out or 10

2. National Institute of Communicable Diseases, Directorate

females collected during a 3 h time span, only I was positive,

General ofHealth Services, Ministry ofHealthand Family

and this positive female contained third or infective stage

Welfare of India (1995): Annual Report.
3. Mahfudin, H., Partono, F., Pumomo and Idris, K. N.

87‑91.

larvae. However, in group C houses, infections were observed

during April, May, Octoberand January of the followlng year.
Earlier filaria vector Cx. quinquefasciatus was also observed
inVaranasi to be positive with mfduring the months of March,
April and May, and again in September and October (1 ,2). In

4. Wijers, D. J. B. and Kiilu, G. (1977): Bancroftian filari‑

the present study, the anthropophilic index was found to beasis in Kenya. ⅠⅠI EntomologlCal investigations in92.0%. It may be due to the fact that the entire collection wasMumbrui, a small town and Jaribuni, arural area more

( 1 977): Parasitological and clinical suⅣey ofBancro氏ianfilariasis in Kepu District, Central Jakarta, Indonesia.

South EastAsian J. Trop. Med., 8, 173‑178.

comprised ofadultsand collected only &om humandwellings.

inland (Coast Province). Ann. Trop. Mらd. Parasito1., 7 1 ,Earlier reports show that the density of an anthropophilic

433‑459.

species is not the only major factor in determlnlng Prevalence

5. Joseph, A. (1971): Studies on the pattem of distributionof filaria carriers in a seaport in Kerala. Indian J. Pub.

of the disease; the relationship between the human host andthe vector densityis equally important (10).

Health., 15, 103‑108.

Duringthe study it was observed that the average humidity
in group C houses was 5.0 to 10.0% higher throughout the6. World Health Organization (1975): Manual on practical0rganization, entomology ln malaria, Part I and II. World

year thanthat of group A and B houses. Earlier reports showthat high humidityis required by the filaria larvae because assoon as the larvae escapes from the proboscis of the infected

7. Collins, 良. T., Dash, B. K.,Agarwala, 良. K. and Dhar,

vector a drop of nuid exudes from the labium and the larvae

for identifying the source of mosquito blood meals.

Health Organization, Geneva, Switzerland.
K. B. (1986): An adaption of the gel di瓜sion techniquemust enter into the bite wound of the human host before thisIndian ∫. Malario1., 23, 8ト89.

8. Kolstrup, N., McMohan, J. E., Magayuka, S. A., Mosa,F. W., Bushrod, F. M. and Bryan, J. H. (1981): Controlfluid evaporates ( I 0). Though the entomological data has not

yet revealed any slgnificant difference between the various
groups of houses, infective mosquitoes prefer to rest indoor,

measures against bancroftian filariasis in coastalvillages

and the high humidityingroup C or poorly constructed houses

in Tanzania. Ann. Trop. Med. Parasito1., 75, 433‑451.
9. Directorate of National Malaria Eradication Programmeof India (1984): Operational Manual. National filaria

probably results in more exposure of their inhabitants toinfective bites, a conclusion which is well supported by thecontrol programme. p. 1 52.

parasitologlCal findings. However, measurement of theintensityoftransmission ofhumanfilarial infection is complex

10. McGreevy, P. B., Kolstrup, N., Tao, J., McGreevy, M.
M･ and Marshal, T. F. de C. (1982): Ingestionand develop‑
ment of Wuchereria bancrofti in Culex quinquefasciatus,
Anopheles gambiae and Aedes aegwti after feeding on

and none of the methods available for measurlng it is ideal.

ACKNOWLEDGMENTS

humans with varylng densities of microfilariae inTanzania. Trans. R. Soc. Trop. Med. Hyg., 76, 288‑296.

The authors are thankful to the Director of the National

110