Infection With More Than One HIV Strain Becoming More Common; Could Complicate Vaccine Development

New research presented yesterday at the International AIDS Society's 2nd Conference on HIV Pathogenesis and Treatment in Paris suggests that HIV "superinfection" -- infection with more than one HIV strain in a single person -- may be more common than once believed, a finding that could complicate HIV/AIDS vaccine development, the AP/Newark Star-Ledger reports. Researchers reported three new cases of HIV-positive people who were not receiving antiretroviral drugs who initially did well but who became sick years later after contracting a second strain of HIV. Luc Perrin, a professor of clinical virology at the University of Geneva, followed 136 HIV-positive drug users and found that the amount of HIV in the blood of five patients jumped up suddenly after years of suppression without treatment. Tests of the five patients confirmed that two of them had superinfection, Perrin said. Harold Burger of Albany Medical College in Albany, N.Y., presented data on genetic tests from an HIV-positive woman whose two HIV strains combined to produce a hybrid that took over from the original virus. Although the development of a hybrid virus was not surprising -- researchers estimate that there are 14 hybrid HIV strains -- the report is the first documented cases of two HIV subtypes combining in one person to form a single new virus, according to the AP/Star-Ledger.

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"Superinfection is sobering," Dr. Anthony Fauci, director of the NIH National Institute of Allergy and Infectious Diseases, said. "That means that, although you can mount an adequate response against one virus, the body still does not have the capability to protect you against new infection, which tells you that the development of a vaccine is going to be even more of a challenge," he added. Anton Pozniak, an AIDS specialist at Chelsea and Westminster Hospital in London, said, "The issue is can you get a vaccine that will cover all subtypes?" He added, "Say you do. Imagine somebody [infected] with a subtype 'C' has sex with someone with subtype 'A' and the two viruses ... combine in some way and suddenly some vaccine, because the infection is an 'A/C,' won't work. Or perhaps and 'A/C' is more virulent and will attack the immune system in a much more aggressive way than either the 'A' or the 'C' -- these are all theoretical possibilities." Pozniak said that researchers know that superinfection is rare but "[w]e just don't know how common it is." Perrin said, "I think superinfection most of the time is transient and is not detected. It may be that you are more frequently infected than you think but that, frequently, you are able to take care of it." However, Pozniak warned that superinfection "reinforces the message that we've got to stop HIV today, so that we can deal with what we have now and not generate a whole load of new mutants that wouldn't have been there otherwise" (Ross, AP/Newark Star-Ledger, 7/15).

A webcast of Fauci's presentation on "20 Years of HIV Science" made yesterday at the conference is available online.

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