United Press International - Wednesday, 11 July 2001
Michael Smith, UPI Science News

Virologist Eric Arts said the C subtype of HIV is spreading more rapidly than other variants, including the B strain most common in North America. But he said laboratory experiments, pitting the strains against each other head-to-head, showed that subtype C does not reproduce as efficiently as B.

"Subtype C has really come on with a fury in southern Africa and now has spread to India and Brazil," he told an audience on the last day of the first International AIDS Society Conference on Pathogenesis and Treatment of AIDS.

One possible conclusion is that subtype C is a more infective pathogen than other strains of the virus, although all can lead to acquired immune deficiency syndrome, AIDS, and eventual death. But, Arts said, when the C type was tested against other variants to see how well it infected white cells and reproduced, other strains won.

"I expected subtype C to win this competition," Arts said, because it is spreading more rapidly than other types.

One possible explanation, he said, is that the C subtype is slower to kill than its counterparts and therefore leaves its victims able to infect more people before they eventually succumb to AIDS. Viruses and other infections tend to evolve to be less deadly over time, Arts said, so they do not kill their hosts too soon. It may be that the C subtype has begun that evolution.

Dr. Douglas Mayers, formerly with Walter Reed Hospital in Washington, D.C., and now with the pharmaceutical firm Boerhinger-Ingelheim, said Arts' finding may be significant.

"He's doing difficult experiments, very difficult, very challenging," Mayers said, "and I have a lot of respect for him." Nevertheless, Mayers said another possible explanation for the result is an experimental flaw. Arts used white cells from North Americans to test African virus and it may be that African HIV is simply better able to invade African white cells and worse at invading others. "He needs to redo the experiment using African cells," Mayers said. If Arts gets the same answer, he said, "then I think it will be very exciting." The head-to-head competition between subtypes would never happen in the real world, Arts said, because each person is infected with a single strain of HIV. But differences between strains found in the lab may be clues to how variants will affect people, he said.

All of the variants of HIV apparently began in Africa in the early years of the last century, he said, but subtype C was rare until about 10 years ago. Arts said he studies people in Uganda, where in 1996 the subtype was unknown. Now it is found in 10 percent of the cases.

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