Ivermectin and the Mectizan Donation Program

River blindness, or onchocerciasis, is caused by the worm Onchocerca volvulus and spread by the bites of blackflies that breed in flowing water. The damage is done by the microscopic larvae the adult worms release: severe itching, disfiguring skin disease and loss of sight, including permanent blindness. More than 99 percent of infected people live in Africa and Yemen.

The drug came from Japanese soil. In 1973 Satoshi Ōmura of the Kitasato Institute in Tokyo began a collaboration with Merck, Sharp and Dohme's research laboratories, sending cultures of soil microbes for testing. In one of the first 50 selected cultures, sent in 1974, William Campbell's team at Merck found a strain, from a soil sample collected near a golf course at Kawana in Ito City, whose broth cleared worms from infected mice. The active compounds were named avermectins, and a chemically modified form, ivermectin, went on sale as a veterinary product in 1981. No other avermectin-producing organism has been found.

When ivermectin proved active against a related Onchocerca parasite of horses, Campbell pressed for a human trial, and Roy Vagelos, then head of Merck research, approved one. In February 1981 Mohammed Aziz of Merck and colleagues from the universities of Dakar and Paris tested it in patients in Senegal and found that it killed the larvae in the skin. French regulators approved ivermectin for human use in October 1987.

Within a month Vagelos, by then Merck's chief executive, announced that the company would donate the drug, as Mectizan, in whatever amounts were needed for as long as needed, and the Kitasato Institute gave up its royalties. In 1998 the donation was extended to lymphatic filariasis in Africa and Yemen, given with albendazole donated by GlaxoSmithKline. Campbell and Ōmura shared half of the 2015 Nobel Prize in Physiology or Medicine. The program reports more than 14 billion tablets shipped since 1987. WHO has verified Colombia (2013), Ecuador (2014), Mexico (2015), Guatemala (2016) and Niger (2025) free of river blindness transmission.