Number of HIV-1 founder variants is determined by the recency of the source partner infection

During sexual transmission, the high genetic diversity of HIV-1 within an individual is frequently reduced to one founder variant that initiates infection. Understanding the drivers of this bottleneck is crucial to developing effective infection control strategies. Little is known about the importance of the source partner during this bottleneck. To test the hypothesis that the source partner affects the number of HIV founder variants, we developed a phylodynamic model calibrated using genetic and epidemiological data on all existing transmission pairs for whom the direction of transmission and the infection stage of the source partner are known. Our results suggest that acquiring infection from someone in the acute (early) stage of infection increases the risk of multiple–founder variant transmission compared with acquiring infection from someone in the chronic (later) stage of infection. This study provides the first direct test of source partner characteristics to explain the low frequency of multiple–founder strain infections.

Tracing the origin and dynamics of the HIV-1 epidemic in Serbia

Since the first report of HIV infection in Serbia in 1985, the HIV-1 epidemic was very dynamic, changing the pattern in subtype distribution and prevailing transmission routes. To better understand the origin and epidemiological dynamics of HIV-1, we analyzed 266 (pol) sequences from Serbian patients diagnosed over a period of 14 years. Subtype distribution in Serbia is still marked by a prevailing subtype B genetic form. The transmission pattern, however, has changed from being intravenous drug user (IVDU) - driven to predominantly sexual transmission. The estimated time of initial founder strain introduction of sequences from Serbian IVDUs and MSM (men who have sex with men) is similar and dates back to the early 1980s, while introduction of subtype C occurred much more recently.