Watching all the news coverage of West Nile disease makes me wonder how doctors can be so sure that AIDS can't be transferred by mosquitoes. Malaria is transferred by mosquitoes. Sleeping sickness is caused by the tsetse fly. If these insects can carry these diseases, why are you so sure they can't carry AIDS?

Mindy

Mosquitoes and other insects are responsible for a tremendous number of illnesses and deaths in the world. Malaria kills about two million people each year. Yellow fever, sleeping sickness, viral encephalitis, Lyme disease and Rocky Mountain spotted fever are also common illnesses transmitted by bugs. However, HIV (the virus that causes AIDS) is not transmitted in this fashion.

Early in the HIV/AIDS epidemic, a major concern was whether everyone would be at risk of infection through contact with mosquitoes or other insects. (In fact, a paper published some years ago alleged that this was occurring in an area in Florida.) Further analysis discredits the theory that bugs can spread the infection. If mosquitoes did indeed transmit HIV, there would be many outbreaks among people with no known risk factors for infection. Children and the elderly, people not likely to be exposed to HIV by sexual contact or intravenous drug use, would commonly be HIV-infected. This is what occurs with viral encephalitis, including infection with the West Nile virus. Everyone is at risk, not just those who have had unprotected sex, shared needles (for injecting drugs) or had another type of exposure known to transmit the virus.

Even in theory, it would be very unlikely that HIV could be spread in such a fashion. With malaria and other insect-borne infections, the organisms survive and actually multiply in the insect. HIV, in contrast, does not survive outside the body for very long, and it does not replicate in insects. In addition, mosquitoes transmit malaria and other infections when they inject saliva into the victim. HIV does not get into the insect's saliva much at all, and mosquitoes do not inject blood into the victim. Furthermore, blood that remains on the bug's mouth or other body parts after it bites an AIDS victim also does not pose much risk, because the amount of blood present is very small, and the insect usually does not go directly from one feeding to another.