To explore the biological similarities and differences between the HIV-I and HIV-2 viruses, we model the probability of male-to-female transmission of either HIV virus as a function of the number of sexual partners, the prevalence of the viruses and the infectivity per contact. Using maximum likelihood estimation theory and data from a prospective study of registered female prostitutes in Dakar, Senegal, we estimate and compare the infectivities of HIV-1 and HIV-2. Graphical goodness-of-fit methods are used to show that our model fits the data well. We find that in male-to-female transmission HIV-1 is significantly more infectious than HIV-2. This finding is consistent with other data from laboratory and epidemiologic studies comparing the biology of HIV-1 and HIV-2.
- Introduction. In 1981 the first cases of the Acquired Immunodeficiency Syndrome (AIDS) were diagnosed in the United States (Centers for Disease Control, 1981). Soon after, a retrovirus (LAV or HTLV III, renamed HIV) was found to be the etiological agent of AIDS (Barr6-Sinoussi et al., 1983;Gallo et al., 1984). This virus was thought to be the only cause of the disease until a second retrovirus associated with an AIDS-like illness was discovered in western Africa in 1986(Barin et al., 1985;Clavel et al., 1986;Clavel et al., 1987).
HIV-2 was given its name to indicate its close relationship to HIV-1, the prototype AIDS virus. This was based on similarities in cell tropism, major antigenic cross-reactivity and genetic properties which include similar genome structure and approximately 50% nucleotide homology (Biberfeld et al., 1987;Kanki, 1987