Human Diet Drugs May Take Bite Out of Mosquitoes

(CN) – Researchers are hopeful they can lessen the spread of mosquito-borne diseases after identifying drugs that reduce the insect’s hunger for blood, according to a study released Thursday in the journal Cell.

Female mosquitoes are to blame for passing infections between humans as the males do not consume blood. After feeding on human blood, this nuisance with wings will lose her appetite for several days before going on the hunt again to nourish eggs of the next generation. Researchers are now working with drug compounds that act on the hormone pathways that signal to a female mosquito that she's full.

"We're starting to run out of ideas for ways to deal with insects that spread diseases, and this is a completely new way to think about insect control," said senior study author Leslie Vosshall, a Howard Hughes Medical Institute investigator and head of the laboratory of neurogenetics and behavior at Rockefeller University, in a statement.

"Insecticides are failing because of resistance, we haven't come up with a way to make better repellents, and we don't yet have vaccines that work well enough against most mosquito-borne diseases to be useful," she said.

Scientists used Aedes aegypti mosquitoes, which spread pathogenic viruses including yellow fever, dengue, Zika, and chikungunya. The species has several broods over the course of its lifetime with each requiring multiple meals. Each time they feed is another chance they will pass on an infectious virus.

Mosquito mothers double their weight with each meal and lose the drive to eat again for about four days, according to researchers. Vosshall and her colleagues hypothesize that certain neuropeptide hormones are responsible for a mosquito's attraction to humans and that feeding temporarily turns these pathways off.

"We know these pathways are important in hunger in humans. Because they are evolutionarily conserved, we made the decision to use human diet drugs to see if they would suppress the appetite of the mosquitoes," Vosshall said. "Finding that the pathways work the same way in the mosquitoes gave us the confidence to move ahead with this research."

The researchers zeroed in on the specific receptor, neuropeptide Y-like receptor 7 or NPYLR7, as the one that signals to the female mosquito whether she's hungry. They then used tissue culture cells to screen for more than 265,000 compounds to determine which ones would activate the NPYLR7 receptor.

Next, they tested 24 of the best compound candidates and found compound 18 worked best. When the mosquitoes with drug number 18 were introduced to the scent of a human or a source of warm blood, their biting and feeding behaviors diminished.

"When they're hungry, these mosquitoes are super motivated. They fly toward the scent of a human the same way that we might approach a chocolate cake," Vosshall said. "But after they were given the drug, they lost interest."

While this is a positive breakthrough, scientists say more work must be done before the compound can be developed for mosquito control. Researchers need to further understand the basic biology of the receptor, how best to exploit it and then how to get mosquitoes to ingest the drug. One idea is a feeder that would attract the females to come and drink the drug rather than drinking blood.

Vosshall believes effective techniques developed from this and related studies will likely work with other kinds of mosquitoes, such as those that spread malaria. Researchers also hope and anticipate their work will transfer to other blood sucking insects including ticks carrying Lyme disease.

While humans would love to avoid the pesky bugs altogether, many other species depend on them for their own survival including birds, bats and other critters. Vosshall lauded the impermanent benefit of the drug to reduce mosquito appetite while not outright killing the bugs.

"It reduces the appetite for a few days, which will also naturally reduce reproduction, but it doesn't attempt to eradicate mosquitoes, an approach that could have many other unintended consequences,” Vosshall said.

The Robertson Therapeutic Development Fund, the National Institutes of Health, a Rockefeller University Women & Science Fellowship, an APS Postdoctoral Fellowship in Biological Science from the American Philosophical Society, and the Howard Hughes Medical Institute provided financial support to the study.

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