ALTITUDINAL VARIATION IN SPECIES COMPOSITION AND INFECTION  RATE OF ANOPHELES MOSQUITOES, AND THE RISK OF MALARIA AND  ITS CONTROL ACTIVITIES IN THE HIGHLAND OF DIRASHE WOREDA,  SOUTH ETHIOPIA
Creators: name: TAYE YOHANNES DAYGENA
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2016

description: Malaria is one of the  most important public health problems  in Ethiopia.  The  changing  climatic 
condition of  highlands  creates a  suitable  environment  for vector  development  and  increase the 
chance  of  malaria  transition  locally,  but  little  information  is  available  on  indigenous  malaria 
transmission in  most highlands. Hence, the current study aimed to investigate variation in species 
composition,  infectivity rates of vectors,   malaria infection  and its control interventions  along the 
altitudinal gradients in  Dirashe Woreda, South Ethiopia.  Longitudinal entomological  study was 
carried  out  in  three  kebeles  (Gato,  Onota  and  Layignaw-Arguba)  from  August  2015  to  April 
2016.  Thirty  houses  were  randomly  selected  (ten  from  each  kebele)  for  biweekly  Anopheles
mosquito collection. The circum-sporozoite proteins  (CSPs)  rate  of  Anopheles  mosquitoes were 
detected using  Enzyme-Linked Immuno-Sorbent Assay  (ELISA). Health  facility  based  malaria 
cases  (August 2015-April 2016) were collected from laboratory registration book of four health 
posts and two health centers to determine malaria cases and  Plasmodium  species in each  kebele.
Malaria control intervention data were collected  from 477 randomly selected households of the 
three  kebeles.  Nine  species of Anopheles  mosquitoes comprising  An.  arabiensis,  An.  demeilloni, 
An. cinereus, An. pharoensis, An. funestus group, An.  pretoriensis, An. christyi, An. ardensis and 
An. tenebrosus   from adult collections and six species such as An. arabiensis, An. demeilloni, An.
cinereus,  An.  An.  funestus  group,  An.  pretoriensis,  An.  christyi  from   larval  collections    were 
documented in the study area.  An.  arabiensis was by far the most dominant in Gato whereas An.
demeilloni  was  the  dominant  species  in  Layignaw-Arguba.  No  An.  arabiensis  were  collected 
from  Layignaw-Arguba  and was rarely found in  Onota. A total of 1102  Anopheles  mosquitoes
were tested for CSPs. Of which five  Anopheleses  were positive  for  P. falciparum  CSP with the 
overall sporozoite rate of 0.45%. The P. falciparum sporozoite rate of An. arabiensis  in Gato was 
0.4% (3/754)  and the  estimated EIR was 8.6  infective bites per person per  nine months.  Two An. 
demeilloni  from Layignaw-Arguba were positive for P. falciparum  CSP and hence its sporozoite 
rate was  0.64%  (2/311).  No  P. vivax  sporozoite positive  An. arabiensis  and  An.  demeilloni  were 
detected.  The  number  of  malaria  cases  was  significantly  different  (p  &lt;001)  with  more  malaria 
cases in  Gato.  P.  falciparum  (including the mixed infection) was the predominant  Plasmodium
species (88%  in Gato and Onota (57.5%), whereas  in  Layignaw-Arguba  P. vivax  (59.4%) cases 
were  dominant. Although malaria cases occurred in all age groups, increased malaria cases were 
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observed in children age 5-14 years in Gato. The scenario was different in Onota and LayignawArguba  where more malaria cases were reported in age group &gt;15 years.  The study revealed that 
92.7% of the  households  in the study  area owned at  least one  LLIN  and overall 77.6% of the 
households  members slept under the  net during the preceding  night of the survey.  The  overall 
LLINs  usage  was  significantly  higher  (86.4%)  in  the  Gato  compared  to  71.3%  in  Onota  and 
64.6% in Layignaw-Arguba (χ
2
= 23.86, DF = 2, P &lt; 0.001). In contrast, the utilization of bed net 
by mothers and under 5 years children were increasing from the  lower altitude  to high altitude.
About 64.4% of the households in Gato were protected by IRS. However, the spray time was not 
considering  the  local  information  and  performed  when  the  indoor  Anopheles  density  was  very 
low and malaria cases  were already built up  and hence,  less likely effective.  In conclusion,  the 
incrimination  of  Plasmodium  positive  Anopheles  species  in  Layignaw-Arguba  justifies  the 
existence of  local  malaria transmission  and the  need of increasing bed nets distribution based on 
the  family  sizes  for  effective  control  of  malaria.  On  the  other  hand,  there  is  a  need  of  further 
investigation  and  confirmation  using  more  sensitive  molecular  techniques  to  consider  An. 
demeilloni as a proven vector of malaria.