Los Angeles County West Vector & Vector-Borne Disease Control District


Can Mosquitoes Transmit AIDS?

    Acquired Immune Deficiency Syndrome (AIDS), the deadly epidemic caused by the HIV virus, is most often transmitted by contaminated hypodermic needles or through sexual contact.  Since mosquitoes feed on human blood and may attack a series of individuals, the question arises: Can you get AIDS from a mosquito bite?
    According to Jonathan F. Day, of the University of Florida's Medical Entomology Laboratory, insects can transmit viruses in two ways, mechanically and biologically.  With mechanical transmission, infected blood on the insect's mouthparts might be carried to another host while the blood is still fresh and the virus is still alive.  Infection by this means is possible but highly unlikely, because mosquitoes seldom have fresh blood on the outside of their mouthparts.  Mechanical transmission does occur in horses, however, with equine infectious anemia, a virus closely related to AIDS and transmitted by horseflies.  These flies are "pool feeders"; their bite causes a small puddle of blood to form, and they immerse their mouthparts, head, and front legs while lapping it up.  If disturbed, however, they quickly move on to another horse, where the fresh blood of the two hosts may mingle.  Blood-feeding mosquitoes are much neater and more surgical; they insert a tube for drawing blood, and by the time they are ready for their next meal, even on a second host after an interrupted meal, any viruses from their first meal are safely stored away in their midgut.
    With biological transmission, the pathogen must complete a portion of its life cycle within the carrier, or vector, species.  Protozoans that cause malaria, for instance, go through an extremely complex cycle inside the mosquito, eventually congregating in the salivary glands, from which they may infect avian, primate, rodent, or reptilian hosts, depending on the malaria species.  The HIV virus, however, does not replicate or develop in the mosquito; once in the insect's gut , the virus quickly dies.  Repeated studies since 1986 show that AIDS-infected blood fed to mosquitoes and other arthropods does not live to be passed on and that, fortunately, there is no biological-transmission cycle of AIDS in blood-feeding arthropods, which frequently ingest the virus as part of their blood meal.




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