Ivermectin, a workhorse of a drug that a few weeks ago earned its developers a Nobel prize for its success in treating multiple tropical diseases, is showing early promise as a novel and desperately needed tool for interrupting malaria transmission, according to new findings presented today at the American Society of Tropical Medicine and Hygiene (ASTMH) Annual Meeting.

Researchers presented preliminary results from a trial in the West African country of Burkina Faso that show approximately 16 percent reduction in childhood malaria episodes in four villages where, for the last few months, the majority of the population has been receiving a single dose of the anti-parasite drug ivermectin every three weeks. The villages are located in an area that experiences a high burden of both malaria and worm diseases, raising the possibility of addressing several health problems at once. 

"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," said Brian D. Foy, the lead investigator on the project from Colorado State University. "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."

There have been previous studies showing ivermectin, even at very low levels, is toxic to the Anopheles mosquitoes that carry malaria. But the trial in Burkina Faso is the only thus far to evaluate ivermectin solely as a strategy to fight malaria disease in sub-Saharan Africa, which is home to the majority of the 584,000 people--most them young children--who die from malaria each year. 

Why Ivermectin for Malaria?

Over the last three decades more than 1 billion doses of ivermectin have been distributed in Africa and Latin America in mass drug administration (MDA) campaigns that have dramatically reduced the burden of lymphatic filariasis, which causes elephantiasis, and onchocerciasis, the disease that causes river blindness. Ivermectin also can kill several types of debilitating intestinal worms known as soil-transmitted helminths.

Earlier this month, the Nobel Prize in Physiology or Medicine was awarded to developers of ivermectin, William C. Campbell of Drew University and Satoshi Ōmura of Japan's Kitasato University, who isolated the precursor of ivermectin from an organism discovered in a single soil sample collected in Japan in the 1970s. The drug was originally used to treat parasites in livestock and pets before becoming the mainstay of the global campaigns to combat lymphatic filariasis and onchocerciasis.

Lead investigator Foy noted that ivermectin's potential efficacy as a malaria control strategy differs from the drug's use against worm diseases because ivermectin is not intended to actually cure a malaria infection. Rather, he said it is intended to reduce infections that lead to fevers in children by interrupting local transmission of Plasmodium parasites. Foy said laboratory studies indicate that when mosquitoes feed on the blood of people who have taken ivermectin, it interferes with the mosquito's ability to transmit malaria parasites to humans--sometimes by killing them outright, but more often by weakening them and interfering with their digestive system so they eventually die in the harsh conditions of nature.

Last year, growing interest in adding ivermectin to the malaria toolkit prompted the creation of the global Ivermectin Research for Malaria Elimination Network to set up a common research agenda for ivermectin-based malaria strategies.