Growth in AIDS Virus Virulence Found

The virus that causes AIDS appears to grow more virulent as the disease progresses, according to a new study at UC San Francisco.

In a report to be published today in the journal Science, Dr. Jay A. Levy, UC San Francisco professor of medicine, said he and a group of researchers discovered the changing virus by studying blood samples taken over a four-year period from four men who were infected by the human immunodeficiency virus, or HIV.

The scientists found that as the AIDS patients became sicker, the virus seemed to evolve and strengthen.

The scientists said this could mean that the virus evolves into more powerful forms as symptoms increase in severity or that a more virulent form of the virus present at the time of infection kicks into action later in the course of the disease.

“I bend toward believing they evolved over time,” Levy said in an interview.

“It’s surprising,” he added. “The virus doesn’t just stay the same, but actually changes its biologic features. It looks like the same virus, but it’s probably evolving within the individual.”

The studies started while all four of the randomly selected subjects tested positive for the HIV virus but had not yet developed acquired immune deficiency syndrome. Three of the men later developed AIDS, and two died. The fourth continues to have no AIDS symptoms even though he tests positive for the virus.

In the three who developed AIDS, Levy said the HIV viruses isolated from their blood samples became more and more virulent as their symptoms intensified. Virulence was tested by exposing the isolated virus to cells in test tubes.

Levy said that when the subjects were experiencing the most severe AIDS symptoms, the HIV from their blood was able to multiply more readily. It also could more easily infect cells and would attack a greater variety of cells.

Viruses isolated periodically from the patient who remained without AIDS symptoms, however, did not show any change in virulence, Levy said.

Levy said it is obvious that the virus must be able to reproduce, or replicate, in order to evolve this increasing virulence. As a result, he said, if researchers can stop the virus from replicating, then it could be kept harmless even though it continued to live within the patient.