Lower HIV-2 plasma viral loads may explain differences between the natural histories of HIV-1 and HIV-2 infections.

To explain the low transmissibility and pathogenicity of HIV-2 infection's plasma viral loads in both HIV-1- and HIV-2-infected persons were compared by using the polymerase chain reaction (PCR)-based Amp-RT assay to measure levels of reverse transcriptase (RT) activity. The study comprised a total of 155 HIV-infected-people including 58 who were infected with HIV-2 with CD4 + cell counts 500 x 10 6 /L (n = 26), or with tuberculosis (TB; n = 17), and 97 HIV-1-infected people with CD4 + cell counts 500 x 10 6 /L (n = 25), or TB (n = 40). Among persons with CD4 + cell counts 500 x 10 6 /L, none of 26 HIV-2-infected persons had detectable RT activity compared with 13 (52%) of 25 HIV-1-infected persons (p 500 x 10 6 /L are associated with a low level of viral replication, which may explain the longer clinical latency and lower transmissibility seen in HIV-2 infection.