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Ivermectin and Malaria
Abstract & Commentary
Alan D Tice, MD, FACP, Infectious Disease Consultant, John A. Burns School of Medicine, University of Hawaii, Honolulu, CA, is Associate Editor for Infectious Disease Alert.
Dr. Tice reports no financial relationships relevant to this field of study.
Synopsis: Ivermectin, an old and safe anti-parasitic medication, may be useful in reducing malaria in hyperendemic areas through administering it to humans and animals to kill the unsuspecting mosquitoes who obtain blood meal.
Source: Chaccour C, Lines J, Whitty CJ. Effect of ivermectin on Anopheles gambiae mosquitoes fed on humans: The potential of oral insecticides in malaria control. J Infect Dis. 2010;202:113-116.
Ivermectin is a well-known anti-parasitic medication that has been used for years, with little toxicity to humans. It has been the mainstay for therapy of onchocerciasis in Africa and Latin America, and also is active against other worms, with effective therapy against strongyloides, ascaris, trichiura filaria, and enterobius. In addition to this, it has taken an increasing role in the treatment of ectoparasites, such as scabies and lice. Ivermectin and other avermectins are derived from Streptomyces avermitilis with their neurotoxic effect via glutamate-gated chloride channels, which are specific for invertebrates.
Ivermectin also is unusual in that it has a half-life of about a day in people and, hence, can persist for a week or more at significant concentrations after oral administration of a single dose. Its use on a once-yearly basis has been quite successful with onchocerciasis, although it kills only the microfilaria. Although ivermectin has been postulated as a potential agent against malaria, it has not generally been used as an insecticide.
A group at the London School of Hygiene and Tropical Medicine took on the question of whether levels of ivermectin after a single oral dose of 200 mcg/kg would affect mosquitoes after being allowed a blood meal. They were able to find 25 volunteers to take the medication and then allow Anopheles mosquitoes to feed on them the day after. Half of the volunteers were given a placebo. The others took ivermectin with minimal or no adverse effects, but the effects on the mosquitoes who fed on them were devastating. They had a mean survival after the feeding of only 2.3 days, compared with the control group, which had a survival of 5.5 days (p < .001). The mosquito mortality rate in the treatment group progressed, with 73% on day 2 after the dose, 84% on day 3, and 89% by day 4 of follow-up. Many of the survivors also were affected by neurologic effects, including lethargy and inability to fly. A second blood feeding was done at day 14 after treatment but the ivermectin group did not differ from the control one at that point.
The authors concluded that ivermectin, in a single standard dose, was well tolerated, and reached blood levels, in otherwise normal humans, that were lethal to mosquitoes that ingested it, none with their blood meal.
Other than the satisfaction of retribution for the humans who live in malaria areas, the authors suggest there may be some opportunities to use ivermectin to control mosquitoes in malarious areas, especially in regions where it is endemic.
Giving people ivermectin may be helpful in malaria areas, but needs further study. In addition, other innocent victims, such as cows and other animals, may serve as carriers of this remarkable agent. The concepts are presently being explored.
Another interesting aspect of ivermectin is that it has somehow managed to avoid the development of resistance by any of the broad range of parasites it affects. How long this will last remains uncertain; field trials are needed.
Perhaps ivermectin will offer some help in containing the age-old scourge of malaria, which continues to regroup and continuously elude the historical methods of control. New ideas such as this may be helpful.