Research published in the Proceedings of the National Academy of Sciences investigating the history of the HIV-2 epidemic has been in the news this month. Unlike HIV-1, which has spread globally, HIV-2 is predominant only in West Africa, where it infects ∼1% of the population. Although both of these viruses are thought to have spread from monkeys to humans, how and when this occurred are questions of considerable debate.

HIV-2 closely resembles the strain of simian immunodeficiency virus (SIV) found in sooty mangabey monkeys. As explained in a report in the New Scientist, to investigate when this virus spread to humans, Dr. Ann-Mieke Vandamme and colleagues from the Katholieke Universiteit Leuven, Belgium, analysed the mutations present in HIV-2 and mangabey SIV and estimated the rate at which these would have accumulated. From this analysis, they concluded that HIV-2 probably crossed to humans as early as the 1940s.

AIDS caused by HIV-2 first occurred in Guinea-Bissau, and levels of infection remained low until the 1960s. As Vandamme told the Associated Press, the sharp increase in disease incidence coincided with the war to gain independence from Portugal between 1963 and 1974, and she speculated that the use of non-sterile injections and increased sexual activity during this time might have been important.

Not all of the coverage of this study has been positive, as reported by HealthScoutNews. Ernest Drucker, a professor of epidemiology at the Montefiore Medical Center and Albert Einstein College of Medicine in New York, has his doubts as to whether HIV-2 really spread to humans this early, and when asked about this work he said, 'The dates are very iffy'.