Abstract:
In Ethiopia, vector control is the principal strategy to reduce the burden of malaria. The
entomological indicators of malaria transmission such as density, sporozoite rate and
entomological inoculation rate (EIR) are the major parameters to assess the impact of vector
control interventions. The susceptibility of the malaria vectors also determines the
effectiveness of insecticide based vector control tools. Hence, the main aim of the study was
to assess the species composition, sporozoite rate and EIR, and insecticide susceptibility
status of malaria vectors. A total of 33 houses (18 for Centre for Disease Prevention and
Control (CDC) light traps and 15 for exit traps) were randomly selected to sample Anopheles
mosquitoes from October 2015 to May 2016. The Plasmodium circum-sporozoite proteins
(CSPs) of An. arabiensis and An. pharoensis were determined using Enzyme-Linked
Immuno-Sorbent Assay (ELISA) technique. Five Anopheles species were identified by CDC
Light traps and exit traps. Anopheles arabiensis (80.2%) was the predominant species,
followed by An. pharoensis(18.5%). Anopheles pretoriensis, An. tenebrosus and An.
rhodesiensis were documented in small numbers. A total of 1056 Anophelesmosquitoes were
tested for CSPs. Of which nine (eight An. arabiensis andone An. pharoensis) were positive
for CSPs with the overall CSP rate of 0.85% (95% CI: 0.3-1.4). Four Anopheles were
positive for P.vivax_210 and 5 were positive for P. falciparum. The P. falciparum CSP rate
of An. arabiensis was 0.46% (95% CI: 0.13-1.2) and it was 0.54% (95% CI: 0.01-2.9) for An.
pharoensis. The EIR of An. arabiensis was 10.1 infectious bites per/person (ib/p)/eight
months. The highest EIR of An. arabiensis was found in February with 4.78 ib/p/month,
following the highest density of An. arabiensis in January 2016.Anopheles arabiensis was
resistant to dieldrin (4%), and deltamethrin (0.05%) with mortality rates of 57% and 71%,
respectively. Permethrin (0.75%) and malathion (0.8%) showed possible resistance with
mortality rates 90.4% and 92.5%, respectively. Anopheles arabiensiswas fully susceptible to
propoxur and bendiocarb.Based on the EIR of An. arabiensis, malaria is endemic in the Sille
village, and the main malaria transmission was occurred from December 2016-February
2016. Hence, supplementary vector control interventions are required as the vector developed
resistance to the insecticides used for impregnation of bed nets.
