Mosquitoes kill more than a million people every year. They transport deadly diseases such as yellow fever and malaria while supping on the blood of unsuspecting victims. The American Mosquito Control Association estimates that malaria alone kills one child every 40 seconds somewhere in the world. The recent work of Colorado State University Prof. Brian Foy seeks to blunt the impact of mosquitoes on human health in a most satisfying way. He plans to make the insects so sick that their malarial parasite hitchhikers don’t live long enough to mature in the mosquito’s salivary glands and thus invade a human host.
The Bill and Melinda Gates Foundation awarded Foy an exploratory grant of $100,000 to perform clinical trials next spring in Burkina Faso, in West Africa. Part of the beauty of Foy’s approach is that no new drugs are involved in the experiment. Ivermectin, a drug currently used to treat worm diseases like river blindness, also has a deadly effect on mosquitoes, but the insect’s role in spreading malaria plays out at a different time of year. Foy will treat villagers with ivermectin during peak malaria season in the spring and see how that impacts the spread of the disease.
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Unlike blanket insecticides, such as DDT, that can exterminate vast numbers of mosquitoes, ivermectin tends to reduce the number of old females — the ones that harbor fully mature malarial parasites. It takes up to two weeks for the malarial plasmodium to complete its life cycle and migrate to the mosquito’s salivary glands where it can be transmitted during a bite. In Foy’s estimation, reducing disease transmission rather than killing mosquitoes in large numbers is a good thing. It lessens the chance that mosquitoes will become resistant to the drug, because there is less intense pressure on the younger breeding part of the population. In practical terms, that means that mosquitoes will still be out and about biting, but fewer of them will be capable of passing on malaria.
Foy also says that ivermectin is “one of the safest drugs out there.” Ivermectin disrupts proteins unique to invertebrates, like worms and insects, and doesn’t cross the blood-brain barrier in humans to cause problems. The World Health Organization dubs ivermectin as an “essential medicine” with moderate possible side effects in humans, including eye irritation, fever, joint pain, tender glands, and rapid heartbeat.
Foy says health personnel administer over a billion doses of ivermectin yearly, counting humans and livestock, although cows, for example, can handle over 10 times the dosage considered safe for humans. Thus, biting a cow becomes a more dangerous proposition for a mosquito than lunching on people.
The Gates Foundation issues their relatively modest hundred thousand dollar grants in batches of 50 or so to various researchers to see which deserve further funding in the $1 million range. Foy is hoping his work next year will earn that additional boost.
Ivermectin doesn’t sicken all mosquitoes equally. It works well against the malarial vector, Anopheles, but not as well against Aedes aegypti, the carrier for dengue fever, chikungunya, and yellow fever diseases. However, as a result of a different grant, Foy has shown that ivermectin does make life difficult for culex mosquitoes, the ones responsible for transmitting the West Nile virus that is now endemic to Colorado.
It would be especially satisfying for Coloradans to make a few of those mosquitoes pay dearly for their blood meals.
Gary Raham is a Wellington-based science writer and illustrator. His new book, “Confessions of a Time Traveler,” featuring several past articles from the North Forty News, will be released next February.