Clade-B HIV-1 infection in Haiti predates global subtype-B virus
Simon Collins, HIV i-Base
Many questions over the epidemiology of HIV, including estimating cross-species infection into humans in the 1930s, and the worldwide development of different clades and sub-populations, have been convincingly explained over the last few years by a combination of phylogentic analyses and molecular modeling. Phylogentic analysis can track viral development and evolution over time by locating specific mutational changes that infer common ancestry. Molecular modeling uses the viral mutation rate to estimate a time frame back in time within which the changes would have occurred.
An oral presentation by Michael Worobey from University of Arizona provided evidence for the geographical origin and timing of sub-type B virus in Europe, Haiti, the US and elsewhere.
The researchers compared archived samples from 1982-3 from five Haitian patients (who had immigrated to the US after 1975, and who were amongst the earliest identified people with HIV in the US), with 117 previously published subtype-B env samples from 19 countries.
HIV in Haiti was traced to a single infection from Africa in or around 1966 (1962-1970), and a single mutation from the Haitian source samples in or around 1969 (1966-1972) was ancestral for almost all non-Haitian subtype B infections around the world. One exception was the subtype B epidemic in Trinidad and Tobago, which was linked to a separate, single-patient introduction from Haiti.
The molecular modeling established the infection in Haiti as the oldest HIV/AIDS epidemic outside Sub-Saharan Africa, and it now includes broader viral genetic diversity than the rest of the worlds subtype B strains combined.
When looking at whether the US epidemic genetically predated that Haitian epidemic (ie was it likely that US travellers took HIV to Haiti or vice versa), their analysis rejected the hypothesis of a US or other non-Haitian origin of subtype B (p <0.001) and strongly supported a Haitian origin (p = 0.999).
Sociological factors supporting these results include the migration of Haitian professionals to work in the newly independent Congo during the 1960s, and that this predated US tourism to Haiti in the mid 1970s.
Other conclusions from this research were that HIV-1 was clearly circulating in the United States for over a decade before the recognition of AIDS in 1981 and that the global spread of HIV-1 involved more inertia than was previously supposed, with major outbreaks hinging on rare, single transmission events, rather than widespread multiple sources of the first infections.
While it is important to understand the history of how the HIV epidemic developed, this still remains a sensitive issue. Documenting the development has no association with blame.
This presentation provided important and fascinating evidence for the pattern of infection. The strongest questions were fielded by an Haitian doctor who highlighted the lack of HIV in historical blood samples from the 1970s. His question appeared to miss the point of phylogenetic research though where viral evolution only moves in one direction.
The presentation was clear that HIV did not start in Haiti, but the calde-B subtype did slowly evolve there before moving to the US and beyond.
Worobey M, Gilbert M, Pitchenik A et al. Exodus and genesis: the emergence of HIV-1 group M subtype B. Oral abstract 149. This oral presentation can be viewed online (Wednesday, 4-6pm, Epidemiology).