Drug can block malaria transmission, studies show
Image by Ute Frevert
and Margaret Shear
PHILADELPHIA—A drug used to treat multiple tropical diseases can also inhibit malaria transmission, according to a pair of studies presented at the ASTMH 64th Annual Meeting.
One study suggests the drug, ivermectin, can reduce the transmission of malaria caused by Plasmodium falciparum, the most prevalent malaria parasite in Africa.
The other study indicates that ivermectin can block the transmission of Plasmodium vivax parasites, which are common in Southeast Asia.
Kevin Kobylinski, PhD, of the Armed Forces Research Institute of Medical Sciences in Bangkok, Thailand, presented results of the P vivax study as abstract 1283.
And Brian D. Foy, PhD, of Colorado State University in Fort Collins, presented results of the P falciparum trial as abstract LB-5237.
P falciparum malaria
Dr Foy and his colleagues are assessing the ability of ivermectin to block malaria transmission in 4 villages in Burkina Faso, Africa.
Lab studies have shown that when mosquitoes feed on the blood of people who have taken ivermectin, it interferes with the mosquitoes’ ability to transmit malaria parasites to humans. Sometimes, it kills the mosquitoes outright, but, more often, it weakens them and interferes with their digestive system so they eventually die in the harsh conditions of nature.
“Even if the mosquitoes don’t get enough ivermectin to directly kill them, we think a sublethal dose should be sufficiently toxic to reduce malaria transmission,” Dr Foy said.
But he noted that because the goal is to interrupt malaria transmission, the drug must be taken by a majority of the people in a town or village, who then pass it along to the mosquitoes.
For the last few months, most of the population in the 4 villages in Burkina Faso has been receiving a single dose of ivermectin every 3 weeks. Individuals who are not eligible to take the drug include children less than 90 cm tall, pregnant women, and newly breastfeeding women.
The measure of success is a reduction in malaria incidence among children younger than 5, most of whom will not actually take the drug. But this is the age group most at risk of serious illness and death from the disease.
Thus far, the researchers have observed a roughly 16% reduction in childhood malaria episodes.
“These are preliminary results, but we expect to see further reductions in malaria fevers as we continue with the trial, which is occurring during the rainy season when malaria transmission typically peaks,” Dr Foy said.
“The drop in malaria fevers we’re seeing with the ivermectin treatment is in addition to whatever is being achieved with insecticide-treated bednets, which are in widespread use in all of the villages participating in the study.”
P vivax malaria
Dr Kobylinski and his colleagues found that ivermectin can affect P vivax parasites as well. The researchers tested the drug’s potential to block malaria transmission by feeding blood meals containing ivermectin and P vivax parasites to Anopheles dirus mosquitoes, the predominant malaria vector in Southeast Asia.
Ivermectin effectively killed A dirus mosquitoes, and it inhibited the ability of any surviving mosquitoes to develop P vivax parasites.
Dr Kobylinski noted that malaria experts are considering combining ivermectin with other medications in mass drug administration (MDA) campaigns that would seek to stop the spread of drug-resistant parasites in Southeast Asia by eliminating malaria from the entire region.
He said ivermectin could help increase compliance with an MDA strategy in places like Thailand, where drug-resistant malaria is spreading but overall malaria infection rates are relatively low.
