Forty-five days. That is how long it took for a fungus to nearly wipe out a population of malaria-carrying mosquitoes inside a giant screened enclosure in rural Burkina Faso.

The enclosure, called the MosquitoSphere, covered about 6,550 square feet and was built to mimic a West African village, with small huts, plants and breeding pools. Researchers released mosquitoes into separate chambers and hung a cloth treated with fungus in each. In the chamber with an ordinary fungus, 455 adult mosquitoes were left after 45 days. In the chamber with no fungus at all, there were 1,396. In the chamber with the engineered fungus, there were 13.

The results, published in Science in 2019, came out of a collaboration between scientists in Burkina Faso and the lab of Raymond St. Leger, a Distinguished University Professor of Entomology at the University of Maryland in College Park. The paper later won the Newcomb Cleveland Prize for the most impactful article Science published that year.

A needle made of fungus

St. Leger, who grew up in England and earned his PhD at the University of Bath, has spent decades studying a group of fungi called Metarhizium. These fungi naturally infect insects. Their spores land on an insect's body, punch through its outer shell and grow inside it.

The natural version is slow, though, and mosquitoes can spread a lot of disease before they die. So St. Leger's team gave the fungus a boost. They engineered it to produce a toxin based on the venom of the Australian Blue Mountains funnel-web spider. The fungus only makes the toxin once it is inside a mosquito.

"You can think of the fungus as a hypodermic needle we use to deliver a potent insect-specific toxin into the mosquito," St. Leger said in a 2019 university release. He has emphasized that the fungi only target insects and are harmless to people. "These fungi are very selective," he said.

Why this matters now

Malaria kills about 600,000 people a year, about 95 percent of them in Africa, according to Maryland Today. Young children in sub-Saharan Africa bear the heaviest burden. Burkina Faso alone had more than 16,000 malaria deaths in 2023.

The main tools for fighting malaria mosquitoes, insecticide-treated bed nets and indoor spraying, are losing ground. Decades of insecticide use have bred mosquitoes that are resistant to it, and some have shifted to biting outdoors, where nets and indoor sprays cannot reach them. In the MosquitoSphere trial, the engineered fungus killed insecticide-resistant mosquitoes just as well as non-resistant ones.

The problem is not as far away as it sounds. As of 2025, the United States had recorded nine cases since 2023 of locally acquired malaria, including one in Maryland, Maryland Today reported.

"It's an arms race between the mosquitoes and us," St. Leger told Maryland Today. "Just as they keep adapting to what we create, we have to continuously develop new and creative ways to fight them."

New ways to deliver it

Since the 2019 trial, St. Leger and his collaborators have focused on a practical question: how do you get the fungus onto mosquitoes in the wild?

One answer is to use mosquitoes themselves. In a 2025 study in Scientific Reports, led by Burkina Faso scientist Etienne Bilgo with UMD researchers, the team coated male mosquitoes, which do not bite, with fungal spores. The males passed the fungus to females during mating. Nearly 90 percent of those females died within two weeks, compared with 4 percent of controls. The university's own release called it a "mosquito STD."

"What makes this fungus particularly promising is that it works with existing mosquito behavior," St. Leger said in the university's release.

Another answer is to lure them in. In October 2025, St. Leger and an international team reported in Nature Microbiology that they had engineered a Metarhizium strain to release longifolene, a sweet-smelling compound that mosquitoes turn out to be drawn to. In lab tests, the fungus killed 90 to 100 percent of mosquitoes, even in a large room with competing human and flower scents. It can be grown on cheap materials like rice husks and wheat scraps, and its scent lasts for months.

"We're letting nature give us a hint to tell us what works against mosquitoes," St. Leger said.

What comes next

None of these strains is in use yet. Larger outdoor trials are underway to support regulatory approval, and modeling suggests the mating strategy would require releasing about 10 treated males for every wild female, every few days, for months. Any genetically engineered organism released outdoors also faces careful scrutiny from regulators and the communities where it would be used.

Still, the work shows how a lab in College Park can be tied to the daily lives of families thousands of miles away. St. Leger has described the motivation simply. "If I want to help people in Africa, I should help with this terrible burden of insect-borne diseases," he told Maryland Today.

And he does not expect the fight to be over anytime soon. "Mosquitoes love many of the ways we are changing our world," he said in 2025. The fungi, at least, have had a head start. As he put it: "The fungi have evolved their own strategies against the mosquitoes."