BackgroundDual infection with HIV-1 and HIV-2, which is not uncommon in West Africa, has important implications for transmission, progression, and antiretroviral therapy. Few studies have examined HIV viral dynamics in this setting.MethodsWe compared HIV-1 and HIV-2 viral loads from 65 dually infected, antiretroviral therapy-naïve Senegalese subjects. Participants provided demographic information and blood, oral fluid, and cervicovaginal lavage (CVL) or semen samples for virologic and immunologic testing. Associations between HIV-1 and HIV-2 levels in plasma, PBMC, oral and genital samples were assessed using linear regression models with generalized estimating equations to account for subjects with multiple samples over time.ResultsIn analyses adjusting for CD4 count, age, sex, and commercial sex work, HIV-1 RNA levels were significantly higher than HIV-2 levels in semen (β=2.05 log10 copies/ml, 95% CI 0.44 to 3.66), CVL (β=1.37, 95% CI 0.83 to 1.91), and oral fluids (β=1.93, 95% CI 1.56 to 2.30). HIV-1 and HIV-2 PBMC viral DNA loads were similar in those with normal immune function (CD4 counts above 500 cells/µl) (β=0.17 log10 copies/µg of PBMC DNA, 95% CI–0.58 to 0.24), but compared to those with high CD4 counts, subjects with CD4 counts below 500 cells/µl had higher HIV-1 and lower HIV-2 levels. In plasma, subjects with CD4 counts above 500 cells/µl had mean HIV-1 plasma RNA viral loads 0.87 log10 copies/ml higher (95% CI 0.35 to 1.38) than HIV-2, while among subjects with CD4 counts between 200 and 500 cells/µl or below 200 cells/µl, this difference increased to 4.28 and 4.35 log10 copies/ml (95% CIs 2.51 to 6.04 and 2.67 to 6.04), respectively.ConclusionOur data are consistent with the hypothesis that with decreasing CD4 counts and HIV disease progression, HIV-1 may out-compete HIV-2 in dually-infected individuals. This finding may help explain the differences in epidemiology between HIV-1 and HIV-2.