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
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.