Scientists Develop ‘Mosquito STD’ to Combat Malaria

The pesky mosquito’s sex life could be its downfall. By creating what amounts to a sexually transmitted disease specifically for mosquitoes, an international team of researchers including a University of Maryland entomologist has unveiled a potentially powerful new weapon in the global fight against malaria.

Published in the journal Scientific Reports earlier this year, the team’s study reveals how this innovative approach exploits mosquito mating behavior to deliver a deadly fungal infection to female mosquitoes—the ones responsible for biting and spreading disease to humans.

The researchers’ invention, which was supported by a National Institutes of Health award, could have wide-ranging implications for controlling malaria, which kills over 600,000 people annually, with children under 5 in sub-Saharan Africa bearing the heaviest burden. In recent years, progress in fighting malaria slowed as mosquitoes developed resistance to chemical treatments and mosquito-borne parasites become more resistant to antimalarial drugs.

“It’s essentially an arms race between the mosquitoes and us,” said study co-author Raymond St. Leger, a Distinguished University Professor in the Department of Entomology. “Just as they keep adapting to what we create, we have to continuously develop new and creative ways to fight them.”

One reason combating mosquitoes—and the deadly diseases they can carry—is so difficult is the speed with which the pests adapt to control methods. As traditional indoor mosquito defenses like bed nets or spraying improved in efficacy, mosquitoes learned to avoid them by lying in wait outside to feed instead.

To target these hard-to-reach mosquitoes, the researchers engineered a naturally occurring fungus called Metarhizium to produce insect-specific neurotoxins that kill when injected into a female mosquito’s body. By spraying male mosquitoes with fungal spores, scientists could ensure the spread of the fungus to the female mosquitoes the males mated with. In tests conducted in Burkina Faso in West Africa, the team found that nearly 90% of the female mosquitoes died within two weeks after mating with males carrying the modified fungus, compared to only 4% mortality in the group without the modified fungus. Though the modified Metarhizium fungus is deadly to female mosquitoes, it is harmless to humans.

“What makes this fungus particularly promising is that it works with existing mosquito behavior rather than against their natural habits,” St. Leger said. “Unlike pesticides or other chemical control methods that mosquitoes can develop resistance to, this method uses the mosquitoes’ own biology to deliver the control agent.”

The researchers also observed that the male mosquitoes treated with the fungus transferred deadly fungal spores to female mosquitoes for up to 24 hours after initial exposure. Thus, male mosquitoes treated with the fungal strain could be released into the environment and continue spreading the fungus through multiple mating encounters.

The presence of the fungus on males did not deter females from mating, and moreover, the fungus boosts the effectiveness of insecticides, “so it’s really a double blow against them,” St. Leger said.

While challenges remain before this “mosquito STD” can be fully deployed at scale, St. Leger noted that the team’s invention represents a significant step forward in humanity’s age-old battle against mosquitoes—and the bites that spread disease.

“Mosquitoes are the world’s deadliest animal. It’s believed that they alone, by transmitting disease, have killed half of all human beings who have ever lived,” St. Leger said. “Being able to eliminate mosquitoes quickly and effectively will save people all over the world.”