Scientists ID First Human With Gorilla Str...(smitted through several people before re...),Health

It's not clear how long the strain has been in existence, but the research suggests that it has made it through several "rounds" of infection, Johnston said.

"The jury is still out as to whether this is bad news relative to strains of HIV that are already circulating," she said. "We just can't draw those kinds of conclusions from one person."

The woman's case is unusual, however, and that fact may be revealing, said Dr. Philip R. Johnson, an AIDS specialist and chief scientific officer at Children's Hospital of Philadelphia.

The level of virus in the woman's body is high but she doesn't appear to have symptoms, potentially suggesting that the strain isn't strong, he said.

In the big picture, it's possible that the disease didn't pass directly from gorillas to humans, but instead took another route, Johnson added.

"More cases will need to be found. The key is that [researchers] now have the tools to look [for them]," he said.

It's possible, he said, that scientists missed similar cases in the past because testing technology couldn't detect them.

More information

Find out more about HIV/AIDS at the U.S. Centers for Disease Control and Prevention.

SOURCES: Rowena Johnston, Ph.D., vice president, research, Foundation for AIDS Research, New York City; Philip R. Johnson, M.D., chief scientific officer, Children's Hospital of Philadelphia, and professor, pediatrics, University of Pennsylvania School of Medicine, Philadelphia; Aug. 2, 2009, Nature Medicine, online