PARIS--An international team of AIDS researchers has identified what appears to be a distinct new strain of HIV-1, the AIDS virus, that is sufficiently different from known strains that it may evade current blood tests. This new strain, isolated from a Cameroonian woman who died of AIDS in 1995, seems to be rare and localized, but experts are urging that tests be modified to pick it up.
The new strain, described in the September issue of Nature Medicine, came to light during a study in Cameroon, led by virologist François Simon of the Bichat Hospital in Paris. Tests of the blood of an AIDS patient failed to detect any virus belonging to the two known groups of HIV-1--the so-called M ("majority") and O ("outlier") groups. But a test for a strain of SIV--the simian version of HIV--isolated earlier from a chimpanzee in neighboring Gabon was positive. When the researchers isolated the patient's virus and sequenced its genetic code, they concluded that it belongs to a previously unknown third HIV-1 group, which they called the N group.
The new strain, designated YBF30, is genetically closer to chimpanzee SIV than other HIV-1 strains, suggesting that its evolutionary ancestors might have been transmitted from chimps to humans. Monkeys and other nonhuman primates are suspected to be the source of other HIV strains. Simon Wain-Hobson, an AIDS researcher at the Pasteur Institute in Paris, cautions, however, that because only a few sequences of chimpanzee SIV are available for comparison, "it's too close a call."
As yet, YBF30 seems not to have spread far: Only three of 700 blood samples from HIV-1 infected patients living in Cameroon tested positive for the strain. Wain-Hobson notes, however, that "the M group probably exploded because it got into urban areas and got there sooner. If you introduce N group viruses into New York, you will get an epidemic." For that reason, the paper's authors recommend that HIV tests be modified to pick up the new strain. Says François Simon: "A continuous search for new variants is necessary to assure the safety of blood donation ... these viruses are on standby, waiting for favorable conditions."