Viral characteristics of transmitted HIV

Purpose of review To summarize our current understanding of the restricted diversity and biological characteristics of newly transmitted HIV-1 variants. Recent findings Transmission of HIV-1 involves a reduction in viral diversity, supporting the concept of a genetic bottleneck. In most cases, transmission appears to be mediated by a single infectious unit. Transmission of multiple variants has also been observed and is associated with factors that compromise the genital mucosa. The biological characteristics of the newly transmitted variants are influenced by the mode of transmission and perhaps the viral subtype. For sexual transmission, the integrity of the mucosal barrier is likely to impose a major restriction on the infecting virus, whereas mother-to-child transmission is also influenced by the presence of maternal antibody. Summary Transmission of HIV-1 is complex, multimodal, and poorly understood, but one common feature appears to be a window of opportunity when the infection is localized and viral diversity is limited; at this time the virus is at its most vulnerable. A better understanding of the restrictions inflicted upon transmitting HIV-1 should therefore lead to improved biomedical interventions that have the potential to protect against HIV infection.