Lower human immunodeficiency virus (HIV) type 2 viral load reflects the difference in pathogenicity of HIV-1 and HIV-2

Human immunodeficiency virus type 2 (HIV-2) is less pathogenic than HIV typ e 1 (HIV-1), but the mechanisms underlying this difference have not been de fined. We developed an internally controlled quantitative reverse transcrip tase-polymerase chain reaction to measure HIV-2 viral load and determined l evels of plasma virus in a cohort of registered commercial sex workers in D akar, Senegal. The assay has a lower limit of detection of 100 copies/mL an d is linear over 4 logs. HIV-2 viral RNA was detectable in 56% of all sampl es tested; the median load was 141 copies/mL. Levels of viral RNA in the pl asma were inversely related to CD4(+) cell counts. HIV-2 and HIV-1 viral lo ads were compared among the seroincident women in the cohort; the median vi ral load was 30x lower in the HIV-2-infected women (P < .001, Wilcoxon rank sum test), irrespective of the length of time infected. This suggests that plasma viremia is linked to the differences in the pathogenicity of the 2 viruses.