Lots of people are talking about this latest paper on HIV. It is an "open access" paper in the PNAS, and you can get it here.
Human immunodeficiency virus (HIV) is a retrovirus that can cause AIDS (acquired immunodeficiency syndrome). It is a member of a larger group of viruses (the Smian immunodeficiency viruses) which are generally thought to be of African origin. There are two types of HIV (HIV-1, and HIV-2), with HIV-1 being the more virulent and, in human populations, most widespread.
There are several theories as to the origin of HIV. When I was in Zaire in the mid 1980s, people in the cities were insisting that several Zairois had been brought to the US and infected with "Sida" (AIDS) and sent back t Zaire unaware of their condition to spread the disease. It has been suggested that HIV was accidentally included in polio vaccine. These and other ideas are highly unlikely, as it turns out.
It is likely that HIV was endemic to certain areas of the Congo for quite a long time. At some point, possibly in the 1970s, the virus started to spread from this area along newly developed truck routes. In the Congo and neighboring countries, a truck is operated by a group generally between four and six men, including drivers and mechanics. These men may travel across several countries with their goods, traveling from Nairobi, Kenya to Kampala, Uganda, to Bunia, Zaire, then into the interior of the Congo, depending on roads, covering several thousand kilometers. This route may be traversed over a period of a few weeks when conditions are good, or a year or more if conditions are bad. Along the route are "truck stops" looking vaguely to the western eye like a motel (kinda, sorta) usually with a small restaurant.
The truck stops also house prostitutes in sufficient number to serve the truckers. Typically, the prostitutes work out of the same truck stop for a long period of time ... the truck stop being located in or near the village in which the prostitute grew up.
Thus, regardless of the sexual practices and mores associated with any given cultural region within the Congo (and there is a great deal of cultural variation there), the truck stop system guarantees that venereal disease will travel across the landscape as quickly as a box of Blue Band Margirine or a Case of Primus Beers. Which means, from a Western perspective, very very slowly as consumer goods go, but very very quickly as disease goes.
So that was probably what HIV was doing for several years in the Congo (then Zaire). In 1981 or 1982, the "AIDS Epidemic" was formerly recognized outside of Africa. So, how and when did HIV-1 go from being something passed around in the Congo to a global pandemic?
There is an early blood sample, taken in 1959, of a man from Kinshasa (then Leopoldville), in the Congo, which shows HIV-1 infection. And there is a 1959 Haitian who may have had AIDS, recognized years later. A few people in the US and elsewhere may have had HIV-1 infection through the 1960s and early 1970s. Some of these cases had known Congolese connections, like a Dr. who died of AIDS in the mid 1970s, and who worked as a surgeon in the Congo.
So while a Hatian connection, or link, between Africa and the Pandemic could have been suspected for some time, the PNAS study strongly underscores this idea and provides important details:
...we propose a geographic sequence and time line for the origin of subtype B and the emergence of pandemic HIV/AIDS out of Africa. Using HIV-1 gene sequences recovered from archival samples from some of the earliest known Haitian AIDS patients, we find that subtype B likely moved from Africa to Haiti in or around 1966 (1962-1970) and then spread there for some years before successfully dispersing elsewhere. A "pandemic" clade, encompassing the vast majority of non-Haitian subtype B infections in the United States and elsewhere around the world, subsequently emerged after a single migration of the virus out of Haiti in or around 1969 (1966-1972). Haiti appears to have the oldest HIV/AIDS epidemic outside sub-Saharan Africa and the most genetically diverse subtype B epidemic, which might present challenges for HIV-1 vaccine design and testing. The emergence of the pandemic variant of subtype B was an important turning point in the history of AIDS, but its spread was likely driven by ecological rather than evolutionary factors. Our results suggest that HIV-1 circulated cryptically in the United States for about 12 years before the recognition of AIDS in
A consensus gene tree showing the relationship between different versions of the env gene of HIV-1. As expected if the above outlined scenario is accurate, the non-Haitian "pandemic" versions are nested within the relatively diverse Haitian clade.
The authors conclude:
Our findings imply that Haiti has the oldest-known HIV/AIDS epidemic outside of sub-Saharan Africa, which helps explain the high prevalence of AIDS and HIV-1 among Haitians in the early 1980s. Because of its 40-year history, the HIV-1 epidemic in Haiti exhibits a greater range of viral genetic diversity than the rest of the world's subtype B strains combined, much as the HIV-1 epidemic in the Democratic Republic of the Congo does for group M as a whole (27). This raises the possibility that subtype B strains in Haiti or elsewhere might exhibit distinct or more diverse antigenic properties compared with pandemic clade viruses. Vaccines derived from consensus or other central sequences should perhaps be based on extensive sampling of Haitian HIV-1 if they are intended to cover both Haitian subtype B strains as well as the pandemic clade.
Although it has long been clear that population bottlenecks and founder effects are a feature of the unfolding HIV/AIDS pandemic, the series of bottlenecks that punctuated the global emergence of subtype B is remarkable. The lack of evidence for selection associated with the spread of the pandemic clade of subtype B, moreover, points to the importance of chance events and ecological interactions in driving what was perhaps the most explosive worldwide dispersal of HIV-1. Our phylogenetic estimates of timing anchor previous epidemiological observations that, on their own, cannot reliably date the origin of regional epidemics. Taken together, these sources of information suggest that HIV-1 was circulating in one of the most medically sophisticated settings in the world for more than a decade before AIDS was recognized.
Gilbert, M. Thomas P., Andrew Rambaut, Gabriela Wlasiuk, Thomas J. Spira, Arthur E. Pitchenik, and Michael Worobey. (2007) The emergence of HIV/AIDS in the Americas and beyond. Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0705329104