A recent study claims to have proved the correlation between HIV-1 RNA in the genital secretions of infected individuals and HIV transmission (Spearman’s rank correlation coefficient ρ was 0.56 for endocervical samples, and 0.55 for semen). Mechanisms of transmission of HIV transmission through genital mucosa are still not well understood. But, prior to this study, there were important grounds for supposing that genital viral load would prove a reliable marker of HIV infectivity – possibly more reliable, where sexual transmission is concerned, than plasma viral load. If definitive evidence has been long coming, this, according to the authors, is due to the logistical difficulties facing the organization of a longitudinal study in which HIV transmission takes place.
The study involved serological sampling from 2,521 heterosexual sero-discordant couples in six African countries, including endocervical swabs from 1805 infected women, of whom 46 were known to have transmitted HIV to their partners, and semen samples from 716 men, of whom 32 were known to have transmitted the disease. Each 1.0 log10 increase in genital HIV-1 was associated with a 2.20-fold (endocervical samples) or a 1.79-fold (semen samples) increased risk of HIV transmission.
This study is in line with the recent research focus on transmission of HIV through genital mucosa and the development of new strategies for blocking HIV transmission through this path, such as topical ARV microbicides. At the close of the discussion section of the paper, the authors draw attention to the potential role of genital sampling in quantifying the reduction in transmission risk from interventions directed at reducing infectiousness of persons with HIV. Among such interventions the principal author mentions, in a recent interview (http://www.medicalnewstoday.com/articles/221595.php), reduction of an HIV person’s infectiveness through HIV treatment, treatment of patients’ other STIs, and microbicides inserted in the vagina. In view of the current interest in the potential of topical antiretroviral microbicides inserted in the vagina, it would be interesting to consider the role that genital sampling of HIV-1 could play as a marker of efficacy in blocking virus transmission.