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HIV-2 transmission: implications for spread of HIV-1.

To the Editor. —Dr De Cock and colleagues 1 summarize data suggesting that human immunodeficiency virus type 2 (HIV2) is less transmissible through sexual intercourse than HIV-1 and conclude that this difference explains the more limited global spread of HIV-2. The authors postulate that the lesser infectivity of HIV-2 is attributable to a relatively lower viral load (and presumably lower levels of virus in semen and female genital secretions) in HIV-2—infected persons with high CD4 + lymphocyte counts compared with HIV-1—infected persons with similar values. The authors also suggest that HIV-2 may be less transmissible because late-stage disease, a period of increased viral load, develops more slowly with HIV-2 infection than with HIV-1. However, the natural history and transmissibility of these retroviruses may be linked by at least two additional factors. First, quantitative studies of HIV-1—infected persons have shown high viral levels during primary infection, 2 and statistical models suggest that