THE IMPACT OF HOUSE SCREENING INTERVENTION ON EXPOSURE TO VECTORS AND ON MALARIA TRANSMISSION, AND THE SUSCEPTIBILITY STATUS OF ANOPHELES ARABIENSIS TO INSECTICIDES IN ARBAMINCH TOWN, SOUTHWESTERN ETHIOPIA: A RANDOMIZED TRIAL

Abstract

House is the major site for malaria infection where most human-vector contact takes places. Hence, screening of houses might reduce the risk of malaria infection by limiting house entry of vectors. This study was assessed the impact of screening doors and windows on indoor density, sporozoite and entomological inoculation rate (EIR) of malaria vectors in malaria hotspot Kebeles (smallest administrative unit in Ethiopia) of Arba Minch town, southwest Ethiopia. The insecticide susceptibility status of Anopheles arabiensis was assessed. Pre-intervention mosquito collection was made by Center for Disease Control and Prevention (CDC) light traps from 92 randomly selected houses. The 92 households were randomized into control and intervention groups. The doors and windows of 46 houses were screened by wire-mesh. Post-intervention mosquito sampling was done by CDC light traps in intervention and control houses. Anophelesmosquitoes were identified into species using a morphological key, and then the circum- sporozoite proteins (CSPs) analysis was conducted using Enzyme-Linked Immuno-Sorbent Assay (ELISA). All the household members both in the intervention and control groups were screened for malaria parasite using a rapid diagnostic test. Anopheles larvae and pupae were collected from natural breeding habitats within the Kebeles, and 2-3 days old female An. arabiensis was tested for susceptibility to insecticide. Probit analysis was employed to calculate the knock down time of An. arabiensis. A Generalized Estimating Equations with a negative binomial distribution was used to see the impact of screening intervention by account for over dispersion of An. arabiensis counts and repeated catches made in the same house. There was a 48% reduction in indoor density of An. arabiensis and it was statistically significant (p = 0.001). The impact of house screening intervention was substantially high (69%) on unfed (active host-seeking) An. arabiensis than other abdominal stages. Plasmodium falciparum CSP rate was 1.6% in houses screened with wire-mesh and 2.7 % in control houses. Screening doors and windows reduced the sporozoite rate of An. arabiensis by 41%, but the reduction was not statistically significant (p>0.05). Screening doors and windows reduced the infectious bites of An. arabiensis by 70%, and the risk of receiving infectious bites was 3.3 times higher in control houses compared to the screened houses. House screening may not affect bed net use rate. Anopheles arabiensis has developed resistance to deltamethrin but was highly susceptible to bendiocarb, propoxur, and malathion. Finally, house screening intervention has played a substantial role byreducing the exposure to malaria vectors, and hence can be recommended as an important intervention to include in malaria vector control package.