Comparing HIV samples from 1986-89 to recent samples, an international team of scientists says the virus that causes AIDS has substantially...

Comparing HIV samples from 1986-89 to recent samples, an international team of scientists says the virus that causes AIDS has substantially weakened since the onset of the pandemic more than 20 years ago.

Reporting today in the journal AIDS, researchers from Case Western Reserve University in Cleveland and the Institute of Tropical Medicine in Antwerp, Belgium, theorized the virus potentially could stop causing disease within 60 years. But the team emphasized that HIV, the pathogen that leads to AIDS, remains a lethal microbe.

Dr. Eric Arts, the U.S. collaborator from Cleveland, wrote with his Belgian colleagues that the findings suggest HIV’s ability to replicate “may have decreased in the human population since the start of the pandemic.”

He drew that conclusion by comparing 12 HIV samples from 1986-89 to 12 samples of the virus from 2002-03. Samples from both eras were from different patients, but closely matched genetically, scientists said, and were studied in petri dishes, where they replicated in a medium of white blood cells, their preferred targets in real-life infection.

Seventy-five percent of the recent samples were weaker on all counts, suggesting they would be less likely to spread in an infected individual or be transmitted to someone else.

The team of scientists theorize the virus could be weakening to better survive in the host; rather than causing death immediately, it has weakened to persist longer.

Dr. Charles Gonzalez, an infectious-disease expert at New York University, said he is not convinced the world is seeing a generalized “weakening” of HIV strains. Two decades is not enough time for such an aggressive pathogen to be on a path toward extinction, he said. “This is too quick,” Gonzalez said.

He also questioned culturing methods, saying it was difficult to make proper samples of the virus two decades ago: “I know that because I was doing sampling then, and I am doing sampling now.”

Dr. Gary Leonardi, chief of virology at Nassau University Medical Center in East Meadow, N.Y., questioned the small number of samples.

“It’s an interesting finding, but 12 samples are not enough,” he said.