Fridae

Doctors once assumed that after initial HIV exposure and infection, the body's immunity response would prevent a second reinfection, should the patient be exposed to another strain of the deadly virus. Swiss researchers have proven this assumption false.

According to a report published in this week's New England Journal of Medicine, researchers in Geneva have documented a case in which a 38-year-old man acquired a second strain of H.I.V. through unprotected sex more than two years after he was first infected in 1998.

The study not only complicates the search for an AIDS vaccine, it makes unprotected sex between two HIV-infected partners even more problematic than previously believed. Exposure to another strain after initial infection can overwhelm treatment regimens and make surviving the disease much more difficult.

"Superinfection may precipitate more rapid progression of the disease," said Doctors Philip Goulder and Bruce Walker of Massachusetts General Hospital, in an editorial in the Journal.

"Infected and non-infected persons should therefore exercise the same degree of vigilance to prevent HIV-1 exposure," they said.

Because sexual activity seems to be increasing among people infected with HIV, they added, "this is a public health message that needs to be broadcast loud and clear."

One researcher, Dr. Bernard Hirschel of the University of Geneva, said the authors had been able to document the case because the patient was enrolled in an AIDS drug study to test early treatment of the virus.

That discovery, said Goulder and Walker, provided "convincing evidence that HIV-1 superinfection can occur long after an initial infection is established."

Because strains of HIV can vary significantly, they said, finding a vaccine against the various forms of the virus "is likely to be a formidable task." Health experts say more than a dozen strains of the virus have been detected around the world.