Bloodmeals from ivermectin-treated cattle reduce survivorship and fecundity of the human malaria vector Anopheles gambiae s.s.

Human malaria occurs broadly throughout the tropics, but the largest malaria burden is experienced in Sub-Saharan Africa, where over 1 million children die annually of this disease. Although insecticide-treated bednets have had some success in controlling vectors, such as the mosquito Anopheles gambiae s.s., malaria transmission persists. It is becoming increasingly clear that malaria transmission in areas of high bednet coverage is due to the propensity of the mosquito vectors to feed on livestock as well as humans. This work quantifies the lethal and sub-lethal effects of two commercially available cattle dewormers: ivermectin and moxidectin, on the malaria vector An. gambiae. Ivermectin, moxidectin, or sterile saline solution was applied to native Kenyan Zebu cattle via subcutaneous injection. Starting 1 day post treatment of cattle, cohorts of mosquitoes were fed on dewormed or saline-injected cattle every three days for up to 23 days post-treatment. Survivorship and egg production within each cohort was quantified. Ninety percent of An. gambiae that fed on ivermectin-treated cattle within 2 weeks of treatment failed to survive >10 days post blood meal. No eggs were deposited by An. gambiae fed on ivermectin-treated cattle within 10 days of treatment. Moxidectin-treated cattle produced no such effect. These results suggest that treatment of cattle with ivermectin could be used as part of an integrated control program to reduce zoophilic vector populations that contribute to malaria transmission.