AIDS virus is very fragile


Q: In the future, could the AIDS virus become airborne?

A: Under almost all circumstances, the answer is no. Unlike some other viruses, the AIDS virus (otherwise known as the Human Immunodeficiency Virus -- HIV) is extremely fragile.

It cannot live outside the body for very long and is sensitive to heat and drying. That is why the two major methods of transmission for HIV remain sexual intercourse and the sharing of needles. Both of these methods allow for the passage of body fluids (which contain the virus) from one person to another. The fluids protect the virus from exposures that otherwise could kill it.

In addition, the AIDS virus is not very infectious. This means that a fairly large number of virus particles must enter the body in order for the infection to take hold. That is one explanation for why AIDS is not transmitted by kissing, however intimate: Saliva contains too few virus particles. In contrast, the Hepatitis B virus is very infectious: a small number of virus particles can trigger an infection. Finally, the AIDS virus cannot penetrate intact skin. It must, instead, gain direct access to the bloodstream through cuts or open sores. Not surprisingly, therefore, people with other infections that cause sores on their genitals (such as herpes or syphilis) are more likely to be infected upon exposure to HIV than people without such sores.

It is true that health-care workers might be infected if they were to be splashed with the blood or other body fluids of someone with HIV infection. But even this is a relatively rare occurrence and would not apply to most people outside a health-care facility.

Taken all together, the known properties of the AIDS virus explain why the routes of infection for HIV are so predictable: the virus, in fairly large quantities, must gain direct entry into the bloodstream. And these characteristics explain why, even if the virus itself became airborne (a very big IF, we wish to emphasize), AIDS would be very unlikely to result from any personal exposure.

Dr. Wilson is director of general pediatrics at Johns Hopkins Children's Center; Dr. Joffe is director of adolescent medicine.

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