High entomological inoculation rate of malaria vectors in area of high coverage of interventions in southwest Ethiopia: Implication for residual malaria transmission.

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 mosquitoes from October 2015 to May 2016. circum-sporozoite proteins (CSPs) of and were determined using Enzyme-Linked Immuno-Sorbent Assay (ELISA). Five species were identified from CDC Light traps and exit traps. (80.2%) was the predominant species, followed by (18.5%). , and were documented in small numbers. 1056 mosquitoes were tested for CSPs. Of which nine (eight and one ) were positive for CSPs with an overall CSP rate of 0.85% (95% CI: 0.3-1.4). Five mosquitoes were positive for and four were positive for _210. CSP rate of was 0.46% (95% CI: 0.13-1.2) and it was 0.54% (95% CI: 0.01-2.9) for . The overall EIR of was 5.3 infectious bites per/person (ib/p)/eight months. 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 , 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.