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Researchers have identified as many as 30 different strains of the AIDS virus that often elude conventional tests used to detect their presence in blood, a Belgian researcher says.

The new strains, first isolated in the central African country of Cameroon, have never been detected in the United States and present no threat now to the American blood supply, J. Richard George of the U.S. Centers for Disease Control and Prevention told the Tenth International Conference on AIDS.But French scientists have identified the viruses, collectively called HIV-1 subtype O, in at least 10 people in Paris, some of whom have no connection to Cameroon. Existing blood tests may eventually have to be modified to ensure they detect the new strains, as well, a recent meeting at the World Health Organization concluded.

Human immunodeficiency virus mutates extremely rapidly, as much as 1 million times faster than most other organisms; that instability has led to a proliferation of different strains of HIV. Genetic information in these different strains can vary by a fraction of a percent or by as much as 30 percent.

Nonetheless, the viruses can be grouped in various ways. Two main types are recognized, HIV-1 and HIV-2.

HIV-1 is the family that causes disease in most of the world, while HIV-2 predominates in areas of West Africa. These two families can further be broken down into eight subtypes, labeled A through H; all these subtypes are readily recognized by existing tests.

The new strains are called subtype O, for "Outliers," because they lie outside the existing subtypes. The subtype O strains do not necessarily resemble each other, however.

The first type O HIV was, in fact, reported at the 1988 International AIDS Conference by Guido van der Groen of the Institute of Tropical Medicine in Antwerp, Belgium. It was dismissed as a "curiosity" of no importance, said Dr. Peter Piot of the World Health Organization.

But van der Groen reported this week that as many as 10 percent of AIDS patients in Cameroon have antibodies to one of the subtype O viruses. The strains are also found in as many as 6 percent of AIDS patients in neighboring Niger and Gabon but not in other nearby countries, he said.