HIV subtype B may have come to the United States from Haiti in a single migration

Studying this pivotal time in HIV/AIDS history could lead to further insight into vaccine design and development.

Issue: December 2007

Nearly all non-Haitian subtype B HIV infections in the world can be traced to a single migration of the virus out of Haiti in or around 1969, according to a new study.

Haiti has the oldest HIV/AIDS epidemic outside sub-Saharan Africa. Because of its 40-year history, the epidemic in Haiti has a greater range of viral genetic diversity than the rest of the world’s HIV subtype B strains combined.

Many new theories about the spread of HIV/AIDS outside of sub-Saharan Africa and when new strains emerged have been introduced by researchers of a recent study. Results were published online in the Proceedings of the National Academy of Sciences of the United States of America.

For the study, researchers combined phylogenetic, molecular evolutionary, historical and epidemiological perspectives to reconstruct the path of the HIV subtype B pandemic to trace the virus back in time and across the world.

Initial migration

The findings suggest that a single migration of a Haitian HIV subtype B virus may have come to the United States and circulated without solid detection in the country roughly 12 years before AIDS was first recognized in 1981. The researchers are the first to provide definitive timelines for the beginning of HIV in the United States.

Researchers said they hope to gain perspective on where the epidemic is going next based on its past.

“The most important thing to know is that it makes no sense to blame any one group that was hard hit by AIDS, but there are numerous benefits to investigating HIV origins,” Michael A. Worobey, PhD, assistant professor in ecology and evolutionary biology at the University of New Mexico, told Infectious Disease News.

Worobey and colleagues studied fossil serotypes to construct the timelines and origin for HIV/AIDS.

HIV-1 group M subtype B was the first discovered HIV virus and is the predominant variant strain outside sub-Saharan Africa.

Using HIV-gene sequences recovered from archival samples of some of the earliest known Haitian patients with AIDS, researchers determined that subtype B most likely moved from Africa to Haiti in or around 1966. The virus remained in Haiti for several years before dispersing to other countries.

The researchers further determined that a single migration of the virus out of Haiti in or around 1969 led to the “pandemic clade,” which includes most non-Haitian subtype B infections in the United States and throughout the world.

Based on this model, challenges in vaccine design and testing arise because Haiti has the most genetically-diverse subtype B epidemic. “We’ve become aware over the years that genetic diversity will be an obstacle to vaccine design because of the need to make vaccines specific subtypes,” Worobey said. “What we’ve found is that the genetic diversity is greater in Haiti than in other countries, and this must be considered in vaccine development.”

The spread of the historically pivotal pandemic variant of subtype B was likely driven by ecological rather than evolutionary factors.

“The next step is to consider the full range of genetic diversity in vaccine testing and to trace the evolution and emergence of HIV back even further,” Worobey said.

“Fossil” samples examined

Most scientists accept evidence that HIV began in Africa and moved to Haiti. The African HIV virus most likely emerged in the 1930s. The timing of a molecular clock showed a likely scenario that it is single-ancestor in the case of HIV subtype B.

“Most of the transmission in the United States is from a single transmission; we don’t know who the person was, but we know that it was around 1969 and was likely of Haitian origin,” Worobey said.

There are no HIV samples that date to the 1960s. Researchers used the earliest samples available (from 1982 and 1983) from the first patients with HIV and constructed evolutionary trees to date the samples back in time. Patients (n=5) were all from the United States. All were recent immigrants from Haiti, and all samples were taken at Jackson Memorial Hospital in Miami. The people were among the first recognized AIDS patients. Complete HIV env sequences and partial gag sequences were also analyzed.

The hypothesis of Haitian HIV origin was tested through Bayesian Markov chain Monte Carlo phylogenetic analysis, which included “relaxed” molecular clock analysis and the alignment of the fossil sequences. Genetic sequences from 117 people with AIDS from 19 countries were also analyzed. The out group was a group of five African strains of subtype D, the closest relative of subtype B.

Researchers used the Los Alamos National Laboratory HIV sequence database for full-length, published env and gag gene sequences of subtypes B and D to plot them within the master sequence.

Using a “relaxed molecular clock” model, researchers estimated the time of the emergence of the most recent common genetic ancestor of subtype B at 1966 based on the years of sampling and other factors. After plotting how quickly the virus evolved over time, the molecular clock was calibrated to place time estimates on the events. The timing of the Haitian HIV emergence supports the theory that the epidemic began in Haiti after Haitian professionals returned from working in the Congo in the 1960s, bringing the first HIV strain with them.

Single migration concluded

The HIV virus moved from Africa to Haiti in a single patient in or around 1966. Almost all non-Haitian subtype B around the world can be traced to the single migration of the virus out of Haiti in 1969, marking a key point in the history of HIV/AIDS, researchers said.

The subtype B epidemic in Trinidad and Tobago, which emanated from a separate single-patient introduction from Haiti, is the only exception researchers found. The conclusions were based on analysis of gene strains’ placements, most importantly if they were nested within the parent strain on the phylogenetic tree. Researchers found evidence for only three events in which the Haitian epidemic seeded outbreaks elsewhere.

Although the single-transmission to global epidemic theory of HIV holds and with a greater inertia than previously concluded, researchers said that there could be some good news for the future, based on the pinpointing of epidemic origin and timelines.

“Our research tells us that most of the attempts by the virus to colonize new areas is a dead end, in areas outside of the epicenter of Africa,” Worobey said. “We may still be getting a relatively small diversity in the HIV virus well into the future, and this is good news.” – by Kirsten H. Ellis

For more information:

Gilbert MTP, Rambaut A, Wlasiuk G, et al. The emergence of HIV/AIDS in the Americas and beyond. Proc Natl Acad Sci U S A. 2007;doi:10.1073/pnas.0705329104. Accessed Nov. 14, 2007.

Worobey M, Gilbert M, Ptichenick A, et al. Exodus and genesis: the emergence of HIV-1 group M subtype B. #149. Presented at: the 14th Conference on Retroviruses and Opportunistic Infections; Feb. 25-28; Los Angeles.