Although several major HIV strains exist, only one type predominates in the United States, leading infected Americans to assume they cannot be reinfected through unprotected sex with one another. But a study of recent infections, published in September in the Journal of the American Medical Association, shows reinfection, called superinfection, with another kind of HIV can and does occur. “What we found was that you could get it again. And when you did, you got it worse,” says study author Davey Smith of the University of California at San Diego.
Smith and his colleagues analyzed stored blood samples from 78 people newly infected with HIV and then compared these with blood drawn from the same people six months to a year later. Their analysis revealed a second, genetically distinct virus proliferating in the blood of three subjects—not a different strain but different enough to suggest a second infection. Worse, these patients began to deteriorate. Within six months the virus load in their blood shot up and their CD4 counts—a measure of immune system function—fell. The presence of the competing viruses diminished the effectiveness of antiretroviral drugs.
An ongoing study presented in July at the International AIDS Conference in Bangkok provided an even more chilling picture in Tanzania, where many HIV types coexist. Following 600 HIV-positive women, Francine McCutchan, of the U.S.-based Henry M. Jackson Foundation, has so far found 28 percent are infected by more than one major HIV strain. There are fears—but as yet no evidence—that such a mix of HIV could recombine in a person to produce a more virulent strain.
In another report at the Bangkok conference, Robert Grant of the Gladstone Institute at the University of California at San Francisco found no competing viruses among 28 couples and 31 individuals with long-standing HIV infections who have unprotected sex with HIV-positive partners. All the subjects had been HIV-positive for more than a year. A second virus may be able to take hold only shortly after the first HIV infection occurs. Smith cautions, “We are dealing with a new weapon of mass destruction here.”