Duration of the mosquitocidal effect of ivermectin

Background. Ivermectin (IVM) reduces the lifespan of malaria-transmitting mosquitoes after feeding on humans treated with IVM. If this effect is sufficiently long and strong, IVM could form part of a drug combination that not only treats malaria patients but also reduces onward transmission. Limited data are available on the exact duration of the mosquitocidal effect of IVM; daily mosquito feeding assays are required for this. Materials and Methods. We determined mortality rates of Anopheles stephensi mosquitoes that took a blood meal on Swiss mice, Wistar rats and Cynomolgus monkeys that received IVM orally at 200-400 μg/kg. Mosquito feeding assays were performed on five consecutive days after IVM administration. Mosquito mortality was determined in the first 72 hours after feeding. Results. Mosquito mortality was 70-100% when mosquitoes fed on any of the animals 1-2 days after the last IVM administration. After this time-point the mosquitocidal effect was still evident in some animals but became more variable. Conclusions. Our findings of a pronounced but short-lived mosquitocidal effect makes the timing of IVM administration crucial to form a useful addition to anti-malarial drugs.