Studies of Susceptibility of Mosquitoes to Insecticides Guide Malaria Interventions in Ethiopia

Entomology technicians collect mosquito larval samples from breeding pools in Asendabo, Ethiopia. Source: RTI/Ethiopia

In Ethiopia, indoor residual spraying (IRS) of houses with insecticide has been one of the primary tools to prevent malaria transmission for more than 40 years. Entomological monitoring activities to study mosquito behavior and their susceptibility to insecticides were originally performed decades ago to inform IRS operations, but were discontinued due to insufficient funding and lack of trained manpower. PMI recently reintroduced these entomological monitoring activities as part of its support for IRS operations in Ethiopia.

Throughout 2009, PMI supported entomological monitoring activities at 11 sites in Oromia Regional State in order to determine and characterize the dominant mosquito species in the area, as well as test mosquitoes’ susceptibility to three classes of insecticides.

Entomology technicians conduct tests to determine if mosquitoes (kept in a cage) are susceptible to certain insecticides. Source: RTI/Ethiopia

The findings from the entomological monitoring activities indicate that Anopheles arabiensis is the predominant malaria vector in Ethiopia and that this mosquito displays varying levels of susceptibility to the tested insecticides. Susceptibility to organochlorine insecticides such as DDT was shown to be low in all sites assessed, with only 0 to 35 percent of mosquitoes killed 24 hours after insecticide exposure. Susceptibility to pyrethroid and organophosphate insecticides was more variable (46 to 76 percent and 68 to 100 percent, respectively), however, and susceptibility to carbamate insecticides was shown to be high (96 to100 percent). The susceptibility to tested insecticides largely depended on prior insecticide use, with organochlorines and pyrethroids having been extensively used in previous IRS operations and in the agricultural sector, respectively.

Ethiopia is currently scaling up IRS activities as one of the interventions to eliminate malaria in the country. “The findings are crucial to ensure that future IRS operations will remain effective and will have the desired impact on malaria transmission,” says Alemayehu Getachew, focal person for PMI’s IRS implementing partner.

Along with its support for IRS operations in Oromia Regional State, PMI will continue to support entomological monitoring activities, as well as assist other in-country malaria stakeholders to expand monitoring activity into other regions of Ethiopia.