Plasma Viral Load in HIV-1 and HIV-2 Singly and Dually Infected Individuals in Guinea-Bissau, West Africa

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Abstract
THE EPIDEMIOLOGICAL and biological characteristics of human immunodeficiency virus (HIV) 1 and HIV-2 exhibit major differences. Whereas HIV-2 is confined mainly to West Africa, HIV-1 is spread globally. Furthermore, the rates of disease progression and transmission are significantly lower in HIV-2 infection.1-4 The reasons for these important differences are not fully understood, but in 1993 De Kock and coworkers5 postulated that differences in viral load may be important. Quantification of HIV-1 plasma viral RNA levels has become widely used for monitoring patients and has been found to have a high prognostic value for clinical progression and response to antiretroviral treatment.6,7 Plasma HIV-1 levels reach a semi-equilibrium (set point, inflection point) after the initial burst of viral replication during primary infection, and this set point is the best available predictor of disease outcome. Commonly, the plasma HIV-1 RNA concentrations reach this lowest level 3 to 6 months after seroconversion and then slowly start to increase. The rate of this gradual increase is determined by the level of the set point.7-9 The information about HIV-2 viral load is limited, and no data on the set point of plasma HIV-2 RNA have been previously published. However, a study by Simon et al10 based on virus isolation and quantification of proviral DNA load in peripheral-blood mononuclear cells indicated that HIV-2–infected patients had significantly lower viral loads than HIV-1–infected patients at corresponding CD4+ T-cell levels. In contrast, a few other studies have shown that the levels of proviral HIV-2 DNA in peripheral-blood mononuclear cells are similar to those in comparable groups of HIV-1–infected individuals.11-13 Two recent studies provided data on plasma HIV-2 RNA levels.14,15 Using different in-house assays, both studies showed lower HIV-2 than HIV-1 plasma viral load in cross-sectional samples, but neither included seroincident cases tested early after seroconversion.