Evolutionary biologists estimate the virus was circulating in North America as early as the 1970s 

We probably know more about HIV than most viruses, but it wasn’t always so. Thirty-five years ago, when the first cases of AIDS surfaced in the US, one of the biggest questions was where did it come from? The mainstream media placed the blame on a French Canadian steward named Gaétan Dugas with HIV, after scientists from the US Centers for Disease Control and Prevention dubbed him as Patient Zero in an epidemiology study. The ensuing coverage had a devastating effect on the man and his family.

In fact, researchers have always been a bit skeptical that a single individual could have sparked the epidemic in North America, and a study published in Nature this week seems to confirm these doubts. The study led by Mark Worobey, an evolutionary biologist from University of Arizona and Richard McKay, an historian from Cambridge University suggests that HIV was probably circulating in North American as early as the 1970s and that it probably arrived here from Africa via the Caribbean.

Worobey, whose earlier work estimated that the HIV pandemic likely began between 1884 and 1924, analyzed thousands of blood samples collected from gay men in the late 1970s, and found enough genetic traces of HIV in several samples that they could sequence them. He and his colleagues ultimately found the strains were similar to ones circulating in the Caribbean during the early 1970s, but variable enough to suggest that multiple strains were already circulating in different parts of the US. The finding closes one of the enduring mysteries of this terrible epidemic, and provides a cautionary tale of what can happen when people form erroneous conclusions based on too little information. “The study is a lesson in how scientifically and ethically difficult it can be to identify a ‘patient zero’, McKay told Nature.  For another perspective on this story, here is the New York Times’ version.