French researchers have isolated a new strain of the AIDS virus in west Africa that appears to have close genetic links to a version that infects nonhuman primates such as chimpanzees.

It's a reminder, they said, of how genetically flexible and cunning the human immunodeficiency virus can be.The new strain so far has been found only in one patient, a 40-year-old woman in Cameroon who died of AIDS in 1995.

French and African officials launched a public health investigation in Cameroon and neighboring Gabon to determine if the new strain is being widely transmitted.

Infectious disease experts are publishing a report on the new strain in Tuesday's issue of Nature Medicine. They said they do not expect it to become prevalent, but it could escape detection by current diagnostic methods used in laboratory screening programs.

"The present isolate is rather a rare bird," said Simon Wain-Hobson of the Institute Pasteur in Paris.

HIV constantly evolves into new strains, even as researchers develop new combinations of therapies to control its proliferation.

The World Health Organization estimates there will be upwardof 40 million AIDS cases caused by many HIV strains by the end of the century.

The researchers said the genetic profile of the new strain is closer to the genes of versions of the viruses found in chimpanzees and other nonhuman primates.