French researchers have identified a human case of a new HIV subtype that is closely related to gorilla simian immunodeficiency virus (SIVgor). Until now, HIV strains in humans have been linked to similar viruses in chimpanzees.

In 2004, soon after moving to Paris, a Cameroon-born woman was tested for HIV. While HIV-1 diagnostic tests detected infection, the subtype could not be determined. Her virus was genetically decoded and computer-analyzed for comparison with other known HIV and SIV types. The woman's infection was a "significant" match for SIVgor.

The new subtype shows no evidence of recombination with other HIV-1 lines, and it is distinct from the three previously known HIV-1 groups M, N, and O, said the authors of the report. As such, the researchers proposed designating the newly detected virus HIV-1 group P.

"The most likely explanation for its emergence is gorilla-to-human transmission of SIVgor," wrote the report's lead author, Jean-Christophe Plantier of the national HIV referencing laboratory at the Rouen Hospital Center, and colleagues.

"For the time being, it's the closest source," said Marie Leoz, a co-author also affiliated with the laboratory. "What is still quite difficult, though, is to date when the first transmission of the virus took place, because there are still very few gorilla strains that are available."

SIV could have been transmitted to humans through a bite or through blood exposure while butchering the animals for food, scientists hypothesize. The prevalence of HIV-1 group P among humans is not known, but it is probably rare, said Leoz. The infected woman has no AIDS symptoms, is receiving treatment, and has a stable viral load and CD4 count, she added.

The full report, "A New Human Immunodeficiency Virus Derived from Gorillas," was published ahead of print in Nature Medicine (2009;doi:10.1038/nm.2016).