Endectocide use in livestock as a tool to help eliminate malaria in Central America

Endectocides are chemicals that are widely used in the livestock industry to control parasites such as intestinal nematodes, ticks, mange mites, lice, and cattle grub. When ingested by mosquitoes in a bloodmeal, endectocides have also been shown to reduce the survival and fecundity of Anopheles malaria vectors. These outcomes provide human health benefits by impacting mosquito vector populations available to bite people. We are evaluating endectocides in Belize, Central America in partnership with local cattle ranchers and investigators at the University of North Dakota.

Malaria is a major health problem throughout the tropical world and is transmitted by a variety of Anopheles mosquitoes. Core vector control interventions consist of indoor residual spraying of insecticides and longlasting insecticidal nets. These are logical strategies in areas where the primary vector species feed at night on people sleeping in their houses and where mosquitoes rest inside the house after blood-feeding. But in Central America, much of the malaria transmission is due to malaria vectors that are exophagic (i.e., prefer to bite outdoors), exophilic (i.e., prefer to remain outdoors), and zoophaghic (i.e., as likely to feed on non-humans as humans). To control mosquitoes with these behavioral characteristics requires a different approach. This proposal addresses the control of zoophagic vectors.

Hypothesis: Targeted use of endectocides in peridomestic livestock can significantly reduce the survival and longevity of zoophagic Anopheles vectors that feed on treated cattle. Because zoophagic vectors are responsible for much of the malaria transmission in Central America, malaria transmission will be reduced in areas where endectocides are given to livestock.

This proposal will determine if endectocides, when administered to cattle, reduces the survival and fecundity of zoophagic malaria vectors in Central America. Significance: If experimental results support the hypothesis, then it is probable that malaria transmission can be reduced in areas where mass drug administration (MDA) of endectocides in livestock is instituted. The logical next step in determining the real-world significance of this approach would be to conduct longitudinal studies to monitor zoophagic vector abundance within rural areas of Central America before and after the institution of endectocidal MDA of local livestock herds.

Publications from the study: Fipronil and Ivermectin Treatment of Cattle Reduced the Survival and Ovarian Development of Field-Collected Anopheles albimanus in a Pilot Trial Conducted in Northern Belize. Dreyer, S. M., Leiva, D., Magaña, M., Pott, M., Kay, J., Cruz, A., Achee, N. L., Grieco, J. P., & Vaughan, J. A. 2019. Malaria Journal, 18(1), 296. 

North Dakota collaborator: Dr. Jefferson Vaughan