100 years of HIV in humans

HIV has existed among human populations for about 100 years, decades earlier than previously believed, according to a study published Wednesday in the journal Nature, the Los Angeles Times reports (Engel, Los Angeles Times, 10/2).

HIV/AIDS was not recognized formally until 1981, and scientists previously estimated its origin at around 1930. However, the new study, led by Michael Worobey of the University of Arizona, found the origin of HIV to be between 1884 and 1924, with a more focused estimate at 1908. Worobey said that the new result "is not a monumental shift, but it means the virus was circulating under our radar even longer than we knew" (Ritter, AP/Google.com, 10/1).

The research is based on lymph node tissue from an HIV-positive woman who died in the Democratic Republic of the Congo in 1960, then the Belgian Congo. The tissue specimen was one of more than 800 preserved in ice-cube-size blocks of paraffin at the University of Kinshasa. The researchers compared that sample with modern HIV strains to determine its mutation rate. They then matched that rate with the oldest sample of the virus -- from a 1959 blood sample taken from a man who also lived in the Belgian Congo -- and traced their common ancestor to between 1884 and 1924, which represents the first appearance of the virus in humans before it mutated (Los Angeles Times, 10/2). "Those old sequences helped calibrate the molecular clock, which is essentially the rate at which mutations accumulate in HIV," Worobey said, adding, "Once you have that rate, you can work backward and make a guess of when the ancestor of the whole pandemic strain of the AIDS virus originated. It is that ancestor we are dating to 1908 plus or minus about 20 years" (Steenhuysen, Reuters Africa, 10/2).

Worobey said that further research is unlikely to determine that the spread of HIV began any earlier than the late 19th century. "I think we're pretty close to where's it's going to end up. It's possible but unlikely we'd find some branch on the evolutionary tree that went deeper," he said (Innes, Arizona Daily Star, 10/2).

It has long been believed by HIV/AIDS experts that HIV descended from a chimpanzee virus. Although it is believed that the chimpanzee virus was transmitted to people in Africa when the animals were killed for bushmeat, the number of other people who contracted the virus were so few that it did not obtain a durable foothold, according to the AP/Google.com (AP/Google.com, 10/1).

According to the researchers, the spread of HIV increased as a result of urbanization during the colonial era (AFP/Yahoo! News, 10/1). "Cities are kind of ideal for a virus like HIV," Worobey said, adding that urban areas provide the virus the opportunity to spread to other people (AP/Google.com, 10/1). Steven Wolinsky, a study co-author from the Feinberg School of Medicine at Northwestern University, said that increased urbanization during the colonial era meant not only more potential hosts for HIV living closer together but also commercial sex work and other high-risk behaviors (Los Angeles Times, 10/2).

Anthony Fauci -- director of NIH's National Institute of Allergy and Infectious Diseases, which helped fund the research -- said the study is "clearly an improvement" over the previous estimate of 1930, calling the advance a "fine-tuning." The AP/Google.com reports that experts are not surprised that HIV circulated among humans for about 70 years before being recognized because an infection usually takes years to produce obvious symptoms, a lag that can mask the role of the virus and which would explain initial low levels among Africans (AP/Google.com, 10/1). Jim Moore, an anthropologist at the University of California-San Diego who was not affiliated with the study, said the fact that HIV could have spread unnoticed for decades is credible, given mortality rates in Africa during the colonial period. "The conditions then were horrendous in terms of how Africans were treated," he said, adding, "People dying of AIDS would have been part of the background" (Los Angeles Times, 10/2). The study also received funding from the David and Lucile Packard Foundation (Arizona Daily Star, 10/2).

The study is available online.