Kersten Koelsch and other researchers at the University of California, San Diego, report that after having identified a man who was infected with both wild-type and drug-resistant strains of HIV, they have concluded that so-called "superinfection" with different strains of the virus may not be as rare as once thought. Scientists had previously believed that the body's immune response to HIV made it resistant to infection with other strains of the virus. But Koelsch, writing in the May 2 edition of the journal AIDS, says that "our findings, together with other recent publications demonstrating HIV superinfection in different clinical settings, indicate that HIV superinfection, even with the same viral subtype, may occur more often than we previously thought."
The researchers reported the case of a California man who was infected with two separate strains of HIV, picking up a wild-type strain months after he was initially infected with a drug-resistant form of the virus. The patient was enrolled in a study of people initially infected with drug-resistant HIV, but researchers detected the second strain four months after the study began. The presence of the second distinct strain of the virus was confirmed with a genetic test that showed the second infection was not resistant to reverse transcriptase inhibitors. Superinfection had a negative impact on the health of the man, who was not taking anti-HIV drugs during the course of the study. His viral load increased from a stable level of 2,400 copies during the first four months of the study to over 200,000 two months later.
Similar cases of superinfection were reported in 2002 by researchers in Boston, Switzerland, and Thailand. Harvard University researchers detailed the case of an HIV-positive Boston man who was infected through unprotected sex during a vacation to Brazil with a second strain of the virus common in South America. The second strain of the virus was shown by genetic tests to be just 12% different from the strain the man initially acquired, but the difference was enough to thwart the effectiveness of the antiretroviral treatment that had kept replication of the original virus in check. The man's viral load surged within just one month of superinfection.
Koelsch and her colleagues conclude that because superinfection has been proved and appears to be more commonplace than initially thought, researchers need to conduct additional studies into how superinfection more quickly impairs the immune systems of HIV-positive people and the role superinfection plays in antiretroviral therapy.