A laboratory study assessing the attractiveness of the malaria vector Anopheles to rabbits treated with a long-acting ivermectin formulation

Abstract

Mass treatment of humans and livestock with ivermectin is seen as a promising strategy in the fight against malaria vectors. However, before implementation of this approach, it is essential to assess whether hosts treated with ivermectin display varying attractiveness to mosquitoes. Our study aimed to assess the attractiveness of Anopheles coluzzii to rabbits treated with ivermectin.

Fourteen rabbits were divided into two groups: an ivermectin -treated group (subcutaneously injected with a long-acting ivermectin formulation, herein IVM) and a control group (subcutaneously injected with the adjuvant of the formulation, herein VHC). Laboratory-reared female An. coluzzii mosquitoes were released into a dual-choice olfactometer impregnated with the odors of IVM-treated or control rabbits between 7 PM and 2 AM, based on four odor combinations (VHC vs IVM, IVM vs empty, VHC vs empty, and empty vs empty). The activation and trophic preference of An. coluzzii were measured in relation to these different odor sources.

The results showed that treatment with IVM did not have a significant impact on the attractiveness of An. coluzzii to rabbits [X2 2 = 47.111; p = 0.48]. However, a slight preference of An. coluzzii towards IVM-treated rabbits was observed at Days 14 and 28 after injection [X22 = 2.9587; p = 0.048]. Ivermectin treatments of rabbits seem not to pose a risk of trophic diversion of the malaria vector An. coluzzii. However, due to the varying attractiveness of Anopheles mosquitoes depending on vertebrate hosts, field trials with natural alternative hosts of Anopheles are required for more powerful conclusions.