Lower levels of HIV RNA in semen in HIV-2 compared with HIV-1 infection: implications for differences in transmission

Background and objectives: HIV-2 infection, in comparison with HIV-1, is characterized by lower plasma viral loads, slower CD4 cell count decline, decreased AIDS-related mortality, and lower rates of mother-to-child and sexual transmission. To gain further insight into why HIV-1 is more readily transmitted as compared with HIV-2, we analyzed semen and plasma HIV RNA levels in HIV-1 and HIV-2-positive men from Senegal. Design and methods: Twenty-two HIV-1 and 10 HIV-2-infected subjects from the University of Dakar donated semen and blood samples for this analysis. HIV-1 and HIV-2 viral loads in semen and plasma were quantified using type-specific polymerase chain reaction assays. Results: The mean age of the subjects was 3 7 and 40 years; mean CD4 cell count was 222 and 276 cells/mu l and the mean plasma viral load was 4.7 and 3.0 log(10) copies/ml for HIV-1 and HIV-2, respectively (P=0.002). HIV RNA was detected in semen in 21 of 22 (95%) of HIV-1 and seven of 10 (70%) of HIV-2-infected subjects; P=0.07). However, the levels of HIV RNA present in semen were markedly different between those with HIV-1 and HIV-2, with a mean of 4.4 log(10) copies/ml among those with HIV-1 and a mean of 2.6 log(10) copies/ml among those with HIV-2 (P<0.001). In multivariate analysis, plasma viral load and HIV type, but not CD4 cell count, were independently predictive of semen viral load (P=0.03, 0.05, 0.48, respectively). Conclusions: These data suggest that differences in semen viral load between HIV-1 and HIV-2 may be in part responsible for the markedly different transmission rates of these two viruses. In addition, risk of male genital tract shedding strongly correlates with plasma viral loads. Interventions that decrease viral load may help decrease transmission of both HIV-1 and HIV-2. (C) 2006 Lippincott Williams & Wilkins.