The researchers surmised that the creation of colonial cities around the turn of the century was the catalyst that allowed the virus to take hold.
Dr. Steven M. Wolinsky, a co-author of the study, said that colonial cities meant not just more potential hosts for viruses living in closer quarters, but also prostitution and other high-risk behaviors for transmitting the virus.
"Urbanization was probably the main trigger," said Wolinsky, an infectious diseases specialist at the Feinberg School of Medicine at Northwestern University in Chicago.
Jim Moore, an anthropologist at UC San Diego who was not associated with the study, said the fact that the virus could have spread unnoticed for decades is no surprise, given the mortality rates in Africa during the colonial period.
"The conditions then were horrendous in terms of how Africans were treated," he said. "People dying of AIDS would have been part of the background."
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mary.engel@latimes.com
