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: 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  observed in children age 5-14 years in Gato. The scenario was different in Onota and Layignaw-
Arguba 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.