A clinical trial published in Lancet Infectious Diseases shows that multiple, high doses of ivermectin are well tolerated and able to kill mosquitoes feeding on humans for up to one month after treatment. In a linked Comment, Regina Rabinovich, from the Harvard TH Chan School of Public Health and director of the Malaria Elimination Initiative at ISGlobal – center supported by the “la Caixa” Foundation- says “this study sets the stage for progress in the development and evaluation of ivermectin for vector control”. The study was funded by the Malaria Elimination Scientific Alliance (MESA), with headquarters in ISGlobal.
Ivermectin is an anti-parasite medicine that has been successfully used to treat worm infections such as onchocerciasis and lymphatic filariasis. It also kills arthropods feeding on a treated individual, including the Anopheles mosquitoes that transmit malaria. Because of this, scientists have started to consider mass drug administration with ivermectin as a potentially powerful tool to help reduce malaria transmission. Importantly, it could kill mosquitoes that can bite outdoors and before dusk (and are therefore not targeted by nets or indoor spraying) and probably also insecticide-resistant mosquitoes. However, the mosquito-killing effects of this drug at a single low dose (i.e. those used for helminth control) are short-lived.
In a trial conducted at Kisumu, Kenya, and led by the Liverpool School of Tropical Medicine, researchers tested the safety and efficacy (in terms of mosquito-killing capacity) of higher doses of ivermectin. They treated 141 adults with uncomplicated malaria with the antimalarial treatment plus either 3 days of ivermectin (600 or 300 µg/kg per day) or placebo. Results show that the blood of patients treated with both ivermectin doses induced high mosquito mortality, even 28 days after treatment. Modelling analysis suggests that adding the 300 µg/kg dose of ivermectin to mass antimalarial drug administration could significantly reduce malaria prevalence by an additional 44% in low transmission settings aiming at malaria elimination.
In her comment, Rabinovich underlines that “given the high variability of the vector and the parasite, it will likely take more than one approach to confront the challenge of malaria elimination. Ivermectin would provide a short-term option, while new endectocides with improved characteristics like longer duration of action are developed.”
Menno R Smit, Eric O Ochomo, Ghaith Aljayyoussi, et al. Safety and mosquitocidal efficacy of high-dose ivermectin when co-administered with dihydroartemisinin-piperaquine in Kenyan adults with uncomplicated malaria (IVERMAL): a randomised, double-blind, placebo-controlled trial. 27 March 2018. https://doi.org/10.1016/S1473-3099(18)30163-4
Regina Rabinovich. Ivermectin: repurposing an old drug to complement malaria vector control. 27 March 2018. https://doi.org/10.1016/S1473-3099(18)30176-2.