CHICAGO --- The most pervasive strain of HIV -- the HIV-1 main (M) group -- began spreading among humans in west-central Africa 60 to 80 years before the AIDS pandemic was first recognized.

New research led by the Northwestern University Feinberg School of Medicine and the University of Arizona indicates that dates for the time of the most recent common ancestor range between 1902 and 1921. The finding will be published in the Oct. 1 issue of Nature.

Researchers recovered viral gene sequences from a paraffin-embedded lymph node tissue biopsy obtained in 1960 from a 48-year-old adult female in Kinshasa in the Democratic Republic of the Congo. This enabled them to conduct the first detailed investigation of the evolutionary history of HIV-1.

The investigation of this strain and other more recent HIV-1 genetic sequences indicated that the rise of cities and high-risk behaviors associated with urbanization may have facilitated the initial establishment and early spread of HIV-1.

"Studies of the evolutionary history of HIV-1 promise to yield new insights into cross-species transmission events and the trajectory of viral genetic diversity," said Steven Wolinsky, senior author and professor of medicine in infectious diseases at the Feinberg School. Wolinsky worked closely with Michael Worobey, assistant professor of ecology and evolutionary biology at The University of Arizona in Tucson, and scientists from institutions around the world to track the history of the virus.

The archival banks of these tissue specimens accumulated by hospitals in west-central Africa provide a vast source of clinical material for viral genetic analysis, according to the paper. The perspective provided by these new sequences from the earliest cases in Africa could yield important insights into the pathogenesis, virulence and evolution of pandemic AIDS viruses.

The National Institute of Allergy and Infectious Diseases co-sponsored the research.