PARIS, France (CNN) -- French researchers have identified a new human immunodeficiency virus, the first derived from gorillas, a report said Monday.
A new virus is difficult to detect by tests because it is not closely related to the other three HIV variants.

A new virus is difficult to detect by tests because it is not closely related to the other three HIV variants.

The three previous HIV variants came from chimpanzees. The new findings indicate that gorillas, in addition to chimpanzees, are likely sources of HIV, the researchers concluded in a report published in the weekly Nature Medicine journal.

The new virus, called RBF 168, was detected in a 62-year-old woman who moved to Paris, France, from the western Africa nation of Cameroon, the report says. She tested positive for HIV in 2004, and researchers led by Jean-Christophe Plantier identified the virus as being closely related to a recently discovered simian immunodeficiency virus (SIV).