The researchers tested both and reported clear results on the mosquito side of the equation:

• The drugs did not affect mosquito survival.
• They did not change feeding behavior.
• They did not impair reproduction.
• Desethylamodiaquine—the active form of one of the world's most widely used antimalarial drugs—was absorbed into the mosquito's circulatory fluid, the insect equivalent of blood.
• Once there, the compound remained detectable for several days.

"To our knowledge, it's the first time that someone has demonstrated that in mosquitoes ingesting long-acting antimalarials via blood meal, the drugs can be absorbed into their circulatory fluid and be present for long periods," Goheen says. "That means that parasites developing in the mosquito are certainly being exposed to these drugs."

In other words, the drugs do not simply sit in the gut and get excreted. They travel through the mosquito's body during the same window in which parasites are maturing.

Why does this matter for drug resistance?

The timing is what makes the discovery significant. Parasites inside a mosquito develop over about 10–14 days, and desethylamodiaquine can persist in the insect for several of those days. That overlap creates a sustained, low-level exposure scenario that scientists have largely overlooked.

Sub-lethal drug exposure is a classic recipe for resistance. If parasites encounter small amounts of an antimalarial while inside the mosquito, the drugs could kill the weakest parasites and leave behind the ones that tolerate the medication. Over many transmission cycles, that could nudge resistant strains toward dominance.

The Yale study does not yet prove this happens. It establishes the exposure. Whether that exposure changes parasite development or fuels resistance is the question Goheen's team is now investigating, working at Yale and in Burkina Faso, West Africa.

"We thought there was a high likelihood that infected mosquitoes are ingesting antimalarials during the time period that parasites are developing within them," Goheen says. "So we wondered, what effect do drugs have on parasites within the mosquitoes?"

What are the study's limits?

The research is in its early stages. The team demonstrated drug absorption and persistence in mosquitoes, not consequences for the parasites themselves. No data yet show that this exposure speeds resistance or alters how parasites mature.

The experiments also focused on desethylamodiaquine, the active form of one widely used drug. Whether other long-acting antimalarials behave the same way inside mosquitoes remains to be tested.

Still, the study reframes how researchers might think about malaria control. Prevention measures already in wide use—medications taken by millions of people in endemic regions—may be quietly shaping the parasites carried by mosquitoes.

"The antimalarial prevention measures that we use may have other impacts on the parasite that we haven't been thinking about," Goheen says. "Gaining a better understanding of how drugs interact with parasites inside mosquitoes could inform future efforts to slow the spread of drug-resistant malaria and help identify new ways to interrupt transmission."

The full paper, by Morgan M. Goheen and colleagues, appears in The Journal of Infectious Diseases (2026), DOI: 10.1093/infdis/jiag300.