Abstract
The HIV-1 CRF02_AG clade is the most prevalent HIV variant in West and West-Central Africa and its detection outside Africa is increasingly common. Little is known, however, about the number and phylodynamics of major CRF02_AG lineages circulating worldwide. To this end, a total of 3170 HIV-1 CRF02_AG-like pol sequences isolated around the world, over a period of 25 years (1989 to 2013), were analyzed using Maximum Likelihood and Bayesian coalescent-based methods. Our results suggest that most of the current CRF02_AG diversity comes from the dissemination of a few founder strains out of Central Africa into West Africa and Cameroon between the late 1960s and the middle 1980s. The CRF02_AG strain introduced into West Africa established a large regional epidemic with low phylogeographic structure. This strain was also successfully disseminated out of the West African region and originated at least three large secondary outbreaks in Cameroon at around the late 1970s, in the former Soviet Union (FSU) countries at around the late 1990s, and in Bulgaria/Germany at around the early 2000s. The CRF02_AG African lineages introduced into Cameroon remained mostly restricted to this country and its neighbors. Demographic reconstructions indicate that major CRF02_AG clades circulating in Africa exhibited a decline in growth rate since the middle 1980s/1990s, whereas CRF02_AG clades in Europe and the FSU countries continue to grow exponentially until the middle to late 2000s. Substantial differences in the median estimated growth rate of the same CRF02_AG clade circulating in different regions (0.63–2.00 year− 1), and of different CRF02_AG clades circulating in the same country (0.41–0.75 year− 1) were observed. Thus, the cause of the epidemic outcome of the different HIV-1 CRF02_AG lineages is probably multifactorial.