Safe sex. Needle exchanges. Vaccine development. Most of the effort to stop the spread of AIDS is aimed at protecting people who are not yet infected. But researchers at Carolina are looking at the problem from a different angle: how to treat people infected with HIV to make them less likely to spread the virus.

"The biology of transmission has been missing from the discussion about HIV," says Myron Cohen, professor of medicine, who, along with Joseph Eron, assistant professor of medicine, heads the research group at Carolina. "We don't know how the virus goes from one person to another."

Cohen and his colleagues think the concentration of HIV in genital fluids must reach a critical level in order to infect another person. Though they don't know what the critical level is, they think that co-infections, such as other sexually transmitted diseases, malaria, and tuberculosis, increase the amount of HIV in genital fluids—an effect called "amplification."

If amplification occurs, it might help explain why the epidemic has hit harder in places such as Africa and Thailand, where co-infections are common. To help answer this question, Irving Hoffman, associate director of the UNC AIDS Control and Prevention Program, worked with a clinical team in Malawi, an African nation where nearly one in five people are infected with HIV.

The researchers collected blood and semen from men who had gonorrhea and from those who didn't and found eight times as much virus in the semen of the men who had the disease. However, virus levels in the blood were the same for the two groups.

"The results start to tell us something about the biology of HIV," Cohen says. "Gonorrhea might increase the HIV levels in semen by stimulating the immune system, causing more virus to be produced."

Once the men were treated with antibiotics, the gonorrhea cleared up in a few hours. After two weeks of treatment, the HIV levels in the men's semen had decreased to the same point as in the men who had never had gonorrhea.

That finding suggests there might be a simple, inexpensive way to slow the spread of AIDS—treat the other sexually transmitted diseases, especially gonorrhea. Such an approach is important in Malawi and other countries that lack resources to treat HIV. It also may be important in North Carolina, which has one of the highest gonorrhea rates in the United States, says Rachel Royce, assistant professor of epidemiology. The researchers have already begun to measure HIV levels in the semen of men in this state to see if a similar amplification can be found.

But antibiotics are not a cure for HIV, Royce says. Despite the reduced virus levels in the semen of the Malawi men, HIV levels in their blood remained unchanged.

To explore the amplification effect further, the researchers are looking at whether malaria and tuberculosis also alter HIV levels. And they want to know whether antiviral drugs and vaccines (once they are developed) will reduce the amount of HIV in the genital fluids of people already infected.

"Treatments that eradicate HIV from genital secretions will end the epidemic," Cohen says. "Treatments that make people feel better but leave HIV present or resistant will make the epidemic worse."

—Elizabeth Zubritsky

This research was funded by the U.S. Agency for International Development, the National Institutes of Health, and the World Health Organization. Results were first presented in July 1996 and were published in the journal The Lancet in June 1997.