Diseases spread by mosquitoes, like malaria and dengue, kill the best part of a million people a year. Vaccines against the diseases and ways to kill the carriers have brought this down, but not enough. Dr Laura Duvall has a new idea, making mosquitoes, and possibly other biting invertebrates, feel as though they have had a full meal so they don't go seeking more.
For most of their life cycle, mosquitoes are vegetarian, living off nectar. However, they need the blood of vertebrates for their eggs to grow, so reproductive-age females turn into the blood-seeking missiles we sadly know.
Rockefeller University's Duvall observed that once a mosquito has enough blood to supply her eggs, she loses interest in pestering humans and goes back to that sweet, sweet nectar. “It's like the ultimate Thanksgiving dinner,” Duvall said in a statement.
This effect has been reproduced using neuropeptides that kill the mosquito's appetite, but the process is not one likely to be usable in the wild. Duvall sought something more practical. She turned to anti-obesity drugs designed to affect NPY receptors that influence hunger.
When Duvall fed some Aedes Aegypti mosquitoes drugs that activate NPY receptors in humans by adding them to saline solution, while feeding others undoped saline, she found dramatic differences in their hunger for human blood. Rather than using the traditional method of having a research assistant stick their arm in a jar of mosquitoes and see how many bite, Duvall tested their hunger by wearing a stocking long enough for it to absorb the human smell and seeing whether mosquitoes flew towards the clothing. Presumably, the saving on bonuses for research assistants is substantial.
Having demonstrated the anti-obesity drugs worked, Duvall reports in Cell her team tested the drugs on all 49 neuropeptide receptors in the mosquito brain and identified NPYLR7 as the affected receptor. Mosquitoes genetically engineered to lack the NPYLR7 receptor retain their desire to feed after meals of human blood that would satisfy their wild-type counterparts.
We don't want to put the entire animal kingdom off their food, so something more specific than releasing anti-obesity drugs into the wild is needed. From 265,000 possibilities Duvall identified one, known as compound 18, that doesn't seem to affect humans, but makes female Ae. Aegypti lose interest in blood meals for several days.
Delivery remains a problem, as well as whether any beneficial species might be affected. However, Duvall is considering options such as using baited traps, or even genetically modifying male mosquitoes to produce a compound 18-like molecule they transmit to females through their semen. She hopes whatever she finds will prove applicable to other mosquito species, such as those that spread malaria, and the flies and ticks that transmit other diseases.