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Second Strain of AIDS Infection Alarms Medical Experts

For people infected with the virus that causes AIDS, anti-viral therapy may not prevent them from becoming infected a second time with HIV. That's the finding of an article published this week in the scientific journal, Nature, about a man who became infected with another strain of HIV, while he was on therapy to control an initial infection.

The lead author of the study, Bruce Walker of the Division of AIDS at Harvard Medical School in Massachusetts, says researchers were "quite surprised and disappointed" when they saw the levels of HIV in the man's bloodstream rise sharply, despite therapy to suppress an earlier infection.

"We had a patient who was doing a very good job of controlling one virus he had been infected with. What we found that was quite surprising was he had actually become infected with a second virus. So, even though his immune system had been capable of very effectively controlling one virus, it wasn't able to protect him against exposure to a second strain of HIV that was closely related to the strain that he was infected with," Mr. Walker said.

The man was part of a study, led by Dr. Walker. Patients were given anti-retroviral therapy, which was periodically stopped to give the body's immune system a chance to work on its own against the virus. The therapy was restored, when the levels of the virus became too high. While the viral levels of all the other patients in the study came down, once they were put back on the drugs, the man's continued to go up.

Sarah Rowland-Jones is a professor of immunology at Oxford University in England and the author of a commentary in Nature. "The reason that that's disappointing for everybody is that that occurred at a time when his immune response to the previous virus, the one that he was actually infected with, was very strong," she said.

Even though it's thought to occur infrequently, Dr. Walker says no one knows how many people are walking around with more than one HIV infection. He says the lesson is that HIV-infected individuals should continue to practice safe sex.