AIDS Virus May Date Back to End of WWII, Study Says
Researchers have tracked down the oldest known specimen of the virus that causes AIDS, a feat that has allowed them to pinpoint the beginnings of the AIDS epidemic to shortly after the end of World War II, a decade earlier than many experts had suspected.
At the same time, another team has identified a new strain of HIV, a finding that some researchers speculate could eventually make identification, treatment and prevention of this disease more difficult.
The newest strain was collected in 1995 from a 40-year-old woman in Cameroon. It is unlike all other strains of human HIV, but is closely related to a chimpanzee virus, Dr. Francois Simon of the Bichat Hospital in Paris told the 5th Conference on Retroviruses and Opportunistic Infections in Chicago.
Although his colleagues have already identified two other patients infected with the new strain, Simon said it is only “weakly detectable” with the tests used to screen for HIV infection.
The discovery of the new strain provides “compelling” evidence that primate viruses continue to cross the bridge into humans, said Dr. Timothy Dondero of the Centers for Disease Control and Prevention.
The oldest specimen of HIV was found in blood collected in 1959 from an adult Bantu man in what is now the Democratic Republic of Congo. Comparison of its genetic material to current strains suggests that HIV first crossed from monkeys to humans shortly after World War II, said Dr. Tuofo Zhu of the University of Washington.
“This paints a pretty nice picture about HIV’s origin and evolution,” said Dr. David Ho of the Aaron Diamond AIDS Research Institute in New York City, where Zhu did the work.
Many researchers had believed that a British sailor who died in Manchester in 1959 was the oldest known case of AIDS, and that the virus emerged around that time. But repeated studies of blood from the sailor have failed to show the presence of HIV, Ho said.
“I would say [Zhu’s study] is the oldest, totally unambiguous look at HIV that we have,” Dr. Simon Wain-Hobson of the Pasteur Institute in Paris writes in this week’s issue of Nature, which also contains a paper detailing the study.
Zhu and his colleagues studied 1,213 blood samples collected in Africa between 1959 and 1982. Only one contained HIV, a sample collected in 1959 in what was the city of Leopoldville in the Belgian Congo. It was from a Bantu man who appeared at a clinic with symptoms of sickle cell disease. No one knows what subsequently happened to him.
The virus in the blood was partially degraded, but the team was able to recover several key fragments, which they compared to other HIV strains.
The AIDS virus mutates extremely rapidly, which has led to an unusually rapid proliferation of HIV strains. Two major types exist, called M and O. M is the oldest and accounts for about 90% of all infections worldwide.
Within type M, however, there are 10 distinct strains, labeled A through I. Type B predominates in the United States and Europe. Type D is the most common strain in Africa.
Using standard genetic techniques, the scientists compared the Bantu’s HIV to all the other strains. They concluded that it was a common ancestor of both B and D. And since all the strains diverged very early, Zhu concludes that the strain in the man’s blood is a primitive form of the virus.
Since the virus is known to mutate at a constant rate, they concluded that it must have jumped from monkeys to humans in the late 1940s or early 1950s.
Charting the virus’ evolutionary change in the past “will help us predict how much the virus will change in the next 10 or 20 years,” said Dr. Anthony Fauci, who heads AIDS programs at the National Institutes of Health.
A few researchers had speculated that some mysterious deaths in Europe during the 1930s were caused by HIV, Ho said. The new discovery, he said, indicates “that is not likely at all.”
Simon’s virus was isolated from a Cameroon woman who later died of AIDS. It is neither type M nor type O, he said. “Clearly, we are dealing with a highly atypical strain of virus,” Simon said. It is, however, very closely related to a simian immunodeficiency virus (SIV) isolated 10 years ago from chimpanzees.
Simon’s team examined 700 other blood samples collected from Cameroon in this decade and found two others that contained the new virus.
Unfortunately, researchers know nothing else about the woman. “That’s very disappointing,” Dondero said. He would like to know whether the woman was from a rural or urban community, whether she lived with a hunter, and if she had cooked and eaten chimps.
Dondero noted that it is not unusual for viruses to pass from animals to humans. But in most cases, like tularemia from rabbits, hantaviruses from mice, and Ebola and Lassa viruses from unknown carriers, the virus does not spread from human to human, or at least not very easily.
“What’s really unusual about HIV is how quickly it has mutated so that it can be easily transmitted from person to person,” he added.
Researchers now know that there were at least four times when immunodeficiency viruses passed from lower primates to humans, he said--once for type M, at least twice for type O and now once for the Cameroon virus. What scientists don’t know, he added, is how many other times such a cross-species transfer has occurred, only to peter out. They also don’t know how many times it will happen again.
