New Strain of H.I.V.

European scientists have discovered a new strain of the virus that causes AIDS and linked it to gorillas, creating a mystery about when and how the first patient found to have the strain became infected.

It is thought to be likely that this is the first time scientists have documented the jump of a simian immunodeficiency virus to humans from a gorilla. All three other known strains of the human immunodeficiency virus, H.I.V.-1, have been linked to chimpanzees. But genetic tests showed that the new virus was closely related to a recently recognized gorilla virus.

The most likely explanation for the new virus’s emergence is gorilla-to-human transmission, probably a result of humans slaughtering apes or handling or eating their meat.

But the scientists said they could not dismiss the possibility that the chimpanzee virus linked to H.I.V.-1 was transmitted to gorillas and then to humans, or was directly transmitted to humans and then to gorillas.

The new virus strain was isolated in 2004 from a 62-year-old woman upon her arrival in Paris from Cameroon in West Africa. She has not been treated for AIDS and has no signs of the syndrome, the scientists said.

The woman had lost weight in 2003 and had been ill with a fever a number of times, the scientists said in reporting the discovery, in the Aug. 2 issue of the journal Nature Medicine.

Her husband died in 1984 from complications of a stroke. It is not known if he was infected with H.I.V. The woman had six children, all born before 1980, a year before doctors first recognized AIDS; two of the children died of noninfectious causes, and none of the surviving children have H.I.V.

The authors of the report said they presumed that she had been infected through sex. The woman told her doctors that she had sexual partners in Cameroon after her husband’s death, but there was no information about whether any were infected — or, if they were, how they had contracted the virus.

The new virus may escape detection by standard blood and laboratory tests for H.I.V.-1. New testing methods developed in recent years have allowed scientists to detect subtypes of H.I.V.-1. The three others are known as H.I.V.-1 Groups M, N and O. Dr. Plantier’s team calls the new one H.I.V.-1 Group P.