The Dallas Morning News - Monday, February 1, 1999
Laura Beil

Although many scientists already suspected the human immunodeficiency virus originated in African primates, the natural lair of HIV has remained a mystery since the disease surfaced almost 20 years ago. Finding the ancestor of AIDS not only solves a long mystery, it may help guide researchers looking for a cure.

After analyzing the genetic makeup of a similar virus that infects chimpanzees, scientists from the University of Alabama at Birmingham say that one subspecies of chimpanzee harbors a virus that gave rise to the current epidemic.

"This species is the source of the human AIDS virus," said Dr. Beatrice Hahn, who presented the work Sunday in Chicago during the annual Conference on Retroviruses and Opportunistic Infections, a meeting that focuses on AIDS. A report will also appear this week in the journal Nature.

Two types of HIV cause AIDS in people. Dr. Hahn studied HIV-1, the type of AIDS virus that has spread worldwide. The origin of the second type, HIV-2, has been traced to the sooty mangabey monkey. HIV-2, which so far has mostly remained in Africa, does not cause disease as quickly as HIV-1, nor is it as easily spread.

The Pan troglodytes troglodytes, the subspecies of chimpanzee thought to have given the disease to humans, are killed for meat in the same west central African region that has been the epicenter for the AIDS pandemic. The chimpanzee's natural habitat is Gabon, Equatorial Guinea and southern Cameroon.

Dr. Hahn and her colleagues believe that slaughtering the animals - "a bloody undertaking," as she called it - exposes the hunters to vast amounts of blood and allows the virus to slip into the human population. The chimps could have also transmitted the virus through bites. Her studies cannot determine when the jump occurred.

But previous research has suggested that the virus that ignited the AIDS pandemic began to smolder in central Africa in the 1940s. That work is based on the genetic analysis of a stored blood sample taken in 1959 from an African man who lived in what is now the Democratic Republic of Congo.

Given the genetic makeup of that virus, which offers clues to the age of the epidemic, the scientists determined that the infection was a relatively recent plague.

But that work couldn't tell the origin of AIDS.

"This is the missing link," said Dr. Douglas Richman of the University of California at San Diego, and chairman of the meeting.

Although they are 98.5 percent genetically similar to humans, chimpanzees don't appear to get AIDS naturally, even when infected. Studying the natural infection in the wild chimpanzee population may reveal knowledge that could help the pursuit of new treatments and a vaccine, researchers said.

The primates pass the virus the same way as humans, through sexual intercourse. Chimpanzees in captivity rarely have the virus because the animals that are used in U.S. research are brought in as babies, before they become sexually active.

This kind of study may be increasingly difficult, however, because the animals are still being slaughtered and have been pushed to the brink of extinction. During her presentation Sunday evening, Dr. Hahn made a plea for the animals' preservation.

A captive chimpanzee named Marilyn who died in 1985 actually harbored the virus that led to the new discovery. Dr. Hahn analyzed stored samples from her, and identified a new strain of simian immunodeficiency virus or SIV. She then compared this virus to three other known infections of SIV in chimpanzees and to HIV-1. The analysis revealed that HIV-1 was similar to the SIV in Marilyn, but not to strains that infect other subspecies of chimps. The common chimpanzee has four subspecies.

"We never knew for sure," Dr. Hahn said of the ancestor of AIDS. "I think now we know it is the chimp."

Dr. Hahn stressed that her research is not out to assign blame for the epidemic. "I would have hoped we are long beyond pointing fingers," she said. "We are in this together. We need to work together to find solutions."

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