How giving mosquitoes diet pills could combat spread of malaria, Zika, dengue

*Scientists discover reducing vectors’ appetite stops them sucking blood
Although mosquitoes do not need to watch their weight, giving the pests diet pills could combat the spread of malaria, Zika and dengue fever.
Researchers found the insects given drugs containing NPY-like receptors were less likely to suck blood when they were presented with a human arm.

These receptors regulate appetite in everything from roundworms to humans, and are even used in experimental anti-obesity medication to curb our desire for food.Scientists believe if female mosquitoes could be coaxed into receiving these drugs, it may help control deadly diseases with limited treatment options.

The research was carried out by The Rockefeller University in New York and led by Professor Leslie Vosshall, from the laboratory of neurogenetics and behavior. Female mosquitoes suck human blood to help their eggs mature, with each insect having several blood-sucking and egg-laying cycles in her life.

This means when a female bites a human with a disease like Zika, she has several opportunities to pass that infection on.Nearly half the world’s population is at risk of malaria, with around 212million cases and 429,000 deaths in 2015 alone, according to the World Health Organization (WHO).

And Zika – which is most commonly found in South America but has spread to the United States (US) – causes birth defects in around one in ten pregnant women who are infected with the mosquito-spread virus. “Preventing mosquitoes from biting humans is an important point of intervention in global public health strategy,” the authors wrote in the journal Cell.

After a female feeds, she stops seeking blood for several days while she allows her eggs to mature. Certain peptides – which make up proteins – have been shown to activate NPY-like receptors.

These suppress a mosquito’s appetite after she has fed.NPY-like receptors have also been shown to influence food intake, fullness and obesity in humans. To test whether drugs containing these receptors could control mosquitoes, the researchers fed NPY-like receptors to females of the mosquito species Aedes aegypti.

This made the insects less likely to seek out food, as well as bite or suck blood, when exposed to a human arm. “When they’re hungry, these mosquitoes are super-motivated,” Professor Vosshall said. “They fly toward the scent of a human the same way we might approach a chocolate cake. After they were given the drug, they lost interest.” NPY-receptors drugs could be administered by drawing mosquitoes into ‘baited traps’ that mimic the signs of a host the insects are attracted to, such as body odour and carbon dioxide.

This may be preferable to other techniques that aim to eradicate mosquitoes – even males ones – despite them being important pollinators and food to many fishes. Existing control methods, such as insecticides, have limited success due to the insects often developing resistance.

Meanwhile, previous infections with dengue virus may have protected some people in an urban slum in Brazil from getting Zika. In a study of more than 1,400 people in the Pau da Lima area of Salvador, those with higher levels of antibodies against a particular dengue virus protein were at lower risk of contracting Zika, researchers report in the Feb. 8 Science. “The higher the antibody, the higher the protection,” says Albert Ko, an infectious disease physician and epidemiologist at the Yale School of Public Health.

That finding contrasts with previous studies in mice and in cells grown in lab dishes, in which antibodies against dengue seemed to make Zika worse.Ko and other researchers had been tracking a rat-borne bacterial illness in the poverty-stricken neighborhood for two years when the Zika outbreak hit in 2015. “We were at the epicenter of the pandemic,” Ko says. Blood samples taken every six months enabled researchers to track people there before, during and after the outbreak.

Zika infected an estimated 73 percent of people in the slum but “it really, really varied geographically,” says Isabel Rodriguez-Barraquer, an epidemiologist at the University of California, San Francisco. In some areas of the 0.17-square-kilometer community, 83 percent of people were infected. In other pockets, just 29 percent were.

Blood tests showed that many of the residents had contracted dengue in the past and had protective antibodies that could ward off Zika, or lessen its ability to cause fever. But “this protection was not absolute,” Ko says. People with a type of antibody, called IgG3 antibodies, indicating recent dengue infection were at higher risk of getting Zika. It’s puzzling why recent, but not older, dengue infections affect Zika risk differently, but that doesn’t necessarily mean that new dengue antibodies directly aid Zika infection, the researchers say. The finding may just mean people who get bitten often by mosquitoes are at higher risk of getting both dengue and Zika.