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Lessons from the second AIDS virus, HIV-2.


 Although the clinical signs and symptoms of human immunodeficiency virus (HIV)-2 are similar to those associated with HIV-1 infection, the former virus has a markedly lower perinatal transmission rate and heterosexual infectivity potential. An ongoing cohort study in Senegal, where the disease was first encountered a decade ago, of 136 HIV-2-infected women found an overall incidence of acquired immunodeficiency syndrome of only 0.18/100 person-years in 548 person-years of observation. Moreover, the rate of developing an abnormal CD4 lymphocyte count from the time of infection onward was 1%/year for HIV-2 infected women compared to 10% for HIV-1. In vitro studies of HIV-2 have shown reduced cell killing, less syncytia formation, and slower viral replication compared to HIV-1. It remains unclear whether viral features alone account for the long clinical latency period and different transmission dynamics of HIV-2. An interesting early finding of the Senegalese study is that partial protection from HIV-1 exists in those already infected with HIV-2. Further delineation of the mechanisms involved in this seeming protective effect should be a high research priority given the potential for prevention of the more virulent HIV-1 strain.
