AIDS Virus May Have Spread to People More Than a Century Ago

The AIDS virus may have first infected humans in Africa in the late 1800s, half a century earlier than previous estimates and decades before mass migration to cities led to its emergence around the world, scientists said.
Genetic analysis of a tissue sample from Kinshasa in the Democratic Republic of the Congo suggests the lethal virus may have spread from monkeys to humans as early as 1884, said Michael Worobey, leader of an international study appearing tomorrow in the journal Nature. Scientists had earlier estimated the first infection took place in the 1930s.

Viruses and bacteria can lurk in animals for decades before showing their ability to sicken people, said Anthony Fauci, head of the U.S. National Institute of Allergy and Infectious Diseases, which funded the work. In the early days of the AIDS virus, eating infected chimpanzees may have caused several isolated infections that failed to spread, he said.

``Then, the sociological conditions were created that turned some of these blips into an explosion,'' Fauci said Sept. 29 in a telephone interview from his office in Bethesda, Maryland. ``An infected person who goes to a city might give it to commercial sex workers, and then you could have the mushrooming of the epidemic.''

AIDS was first identified in a few U.S. patients in 1981. Today, 33 million people worldwide are infected with HIV, the human immunodeficiency virus that causes it, according to UNAIDS, the United Nations office that coordinates the agency's response to the disease. About 2.7 million people became infected with the virus last year, UNAIDS said in July.

Virus From Chimps

HIV is descended from a chimp virus, and hunters were probably the first humans to come into contact with it, Fauci said. The earliest known infected human tissue sample was obtained in 1959, and is also from the Kinshasa area, he said.

Scientists compared genes from that sample, preserved in wax, with another that had been taken in 1976 to estimate HIV had begun spreading in people in the 1930s. The newly acquired sample from 1960 showed that viruses infecting humans in the same geographical area had already gained a large degree of genetic diversity, said Worobey, an assistant professor in the University of Arizona's department of ecology and evolutionary biology in Tucson.

That diversity took decades to accumulate, suggesting that humans were first infected between 1884 and 1924, Worobey's team said in the study. That coincides with the establishment of urban centers in the region, including Kinshasa in 1881, they said. The city that's now home to 7 million people was founded and named Leopoldville by the explorer Henry Stanley.

Snapshot of Virus

``We've gone from making our best guesses about these events deep in the history of the pandemic to having a direct snapshot,'' Worobey said Sept. 26 in a telephone interview. ``These sequences show the genetic diversity of the virus in 1960. It snaps everything into clear focus.''

Worobey's team, which included scientists from Kinshasa, Australia, Denmark and Belgium, used new techniques to extract DNA from tissues that have been preserved for decades. Preservatives used on the tissues, such as formalin, can break down genetic material, he said.

Worobey began searching Africa for old tissue samples that might contain HIV in 2001. He said that he had just been talking with a colleague about how much more difficult the study was to do than he anticipated, ``and we were laughing about how hard it was.''