The mosquito is regularly crowned the most deadly animal on Earth, and with good reason. Infectious diseases spread by these insects—including malaria, dengue, and Zika—mean mosquitoes are responsible for 725,000 human deaths every year.
Rather than looking for a vaccine for each of these different diseases, what if we made a vaccine against mosquitoes themselves?
That's exactly what scientists have done, and they're about to test it on humans for the first time. The vaccine, called AGS-v, was developed by researchers in London and is about to be tested through a small trial conducted by the National Institutes of Health.
Here's how it works: researchers have learned that mosquitoes' saliva is spiked with a cocktail of proteins that makes it easier for them to feed. When a mosquito bites you, these proteins interact with your body and cause a number of changes that help the skitter to suck up some blood: your blood vessels dilate, your blood thins a little bit, and your body's immune response is disabled very slightly.
But the real trouble lies in the pathogenic organisms that a mosquito might carry, such as the Zika virus or the malaria parasite. These organisms take advantage of the mosquitoes' effects on your body after the bite to infect you without immediate detection from your immune system.
"You have to try not to anthropomorphize," said Dr. Matthew Memoli, the director of the Laboratory of Infectious Diseases clinical studies unit at the NIH. "It's not like the mosquito is purposely making saliva that does something to help the organism. It's just a natural relationship that this is happening—it's the way everything evolved."
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The AGS-v vaccine is designed to stimulate an immune response in humans by injecting some of these mosquito-spit proteins, but in a higher level than you would get from a mosquito bite. The idea is that, if your body learns to recognize these proteins as a threat through the vaccine, the next time a mosquito bites you, your body can counteract their effects: ideally, there will be no dilated blood vessels, no blood thinning, and most importantly, no hit to the immune system.
"Because you've been sensitized, you won't respond in the same way and you'll have enough of an [immune] response that you'll stay protected from whatever the organism is that's trying to infect you," Memoli told me.
The vaccine has been tested on rabbits and mice, with some promising results, but this will be the first time it's tested in humans. The NIH will enlist 60 adults and give them either two doses of the vaccine or two doses of a placebo. About a month after the second dose, the participants will have to come in and offer up their arm to (disease-free) mosquitoes, to see what kind of response their bites provoke.
Memoli told me there's a chance the vaccine won't work entirely on its own, but it could be a kind of booster for other disease-specific vaccines. So a malaria vaccine may target the parasite, while this vaccine targets the mosquito, and together they could provide broader protection against infection.
"Mosquitoes that fed on mice that received this vaccine also didn't survive as long as mosquitoes that fed on animals that did not receive the vaccine," Memoli said. "There's potential that this could not only help prevent a person from becoming infected but also prevent mosquitoes from taking good blood meals and surviving to reproduce, which would ultimately be good for reducing spread of the disease."
If even one of these angles for the vaccine turns out to be effective, it could be a real boon to the fight against mosquito-spread infection diseases and may finally knock the world's most deadly animal down a few pegs.
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