Though a wet spring and warm winter mean conditions are ripe for a truly heinous plague of mosquitoes to descend on much of the U.S. this summer, at least there's one disease you don't have to worry about when you're covered in bites: AIDS.
The U.S. Centers for Disease Control says that the body of scientific literature has shown no evidence of HIV transmission from mosquitoes or any other insects-even in areas where there are many cases of AIDS and large populations of mosquitoes.
One reason that the AIDS virus isn't transferred is that the mosquito does not inject its own blood - or the blood of its last meal - when it bites a person. Instead, it's injecting saliva, which it uses as a lubricant to aid its feeding. (Mosquito-borne diseases like malaria and yellow fever, however, are transferred through the insect's saliva).
Also, since the insect draws blood up a passage that's completely separate from the one that delivers saliva, there's little chance that HIV-contaminated blood would be transferred when a mosquito regurgitates saliva into its next victim.
It's also incredibly statistically unlikely that a mosquito would take up enough particles of HIV to infect a new host. In HIV-infected people, there aren't a lot of particles of the virus in circulation as compared to the amount of agents in known mosquito-borne disease.
People infected with HIV rarely have more than 10 units of HIV circulating in their bloodstream. According to the University of Rutgers Center for Vector Biology, even if a mosquito was feeding on a person that had 1,000 circulating units of HIV, calculations have shown that there's a 1 in 10 million chance that the mosquito would then inject a single unit of HIV to the next person.
In laymen's terms, an AIDS-free individual would have to be bitten by 10 million mosquitoes that had begun feeding on an AIDS carrier to receive a single unit of HIV from contaminated mosquito mouthparts, Rutgers entomologist Wayne J. Crans wrote on the Center's website.
But one of the main reasons that mosquitoes can't transmit HIV is that they digest the virus. Other mosquito-exploiting parasites have ways of evading the mosquito's digestion enzymes. Many parasites bore out of the insect's stomach; others have defenses against the enzymes themselves. In 2010, researchers from the U.S. National Institutes of Health found the malaria parasite hiding in a network of proteins that the mosquito makes in its midgut to protect the beneficial bacteria that grow in its gut, using the insect's own defenses to escape its immune system.
But HIV has no such tricks up its sleeve (for now).