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 parameters used to assess the impact of the interventions and
the intensity of malaria transmission. The susceptibility of malaria vectors also determines the
effectiveness of insecticide based vector control tools. Hence, the aim of the study was to assess
the species composition, sporozoite rate and EIR, and insecticide susceptibility status of malaria
vectors.
33 houses (18 for Centre for Disease Control and Prevention (CDC) light traps and 15 for exit
traps) were randomly selected to sample Anopheles mosquitoes from October 2015 to May 2016.
Plasmodium circum-sporozoite proteins (CSPs) of An. arabiensis and An. pharoensis were
determined using Enzyme-Linked Immuno-Sorbent Assay (ELISA).
Five Anopheles species were identified from CDC Light traps and exit traps. An. arabiensis
(80.2%) was the predominant species, followed by An. pharoensis (18.5%). An. pretoriensis, An.
tenebrosus and An. rhodesiensis were documented in small numbers. 1056 Anopheles mosquitoes
were tested for CSPs. Of which nine (eight An. arabiensis and one An. pharoensis) were positive for
CSPs with an overall CSP rate of 0.85% (95% CI: 0.3–1.4). Five Anopheles mosquitoes were
positive for P. falciparum and four were positive for P.vivax_210. 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 overall EIR of An. arabiensis was 5.3 infectious bites per/person (ib/p)/eight months. An.
arabiensis was resistant to dieldrin (mortality rate of 57%) and deltamethrin with mortality rates
of 71% but was fully susceptible to propoxur and bendiocarb. Based on the EIR of An. arabiensis,
indoor malaria transmission was high regardless of high coverage of indoor-based interventions.
Finally, there was an indoor residual malaria transmission in a village of high coverage of bed
nets and where the principal malaria vector is susceptibility to propoxur and bendiocarb;
insecticides currently in use for indoor residual spraying. The continuing indoor transmission of
malaria in such village implies the need for new tools to supplement the existing interventions
and to reduce indoor malaria transmission.