Background: The emergence and rapid world-wide spread of HIV provides an unusual opportunity for the study of the evolution and maintenance of virulence in a major human pathogen.
Objective: To analyse the available biological and epidemiological data on the pathogenicity, transmissibility and antigenic similarity of HIV-1 and HIV-2, and use simple mathematical models of competition between the two viral types within a defined host community.
Results and conclusions: Analysis revealed a positive association between pathogenicity and reproductive success. A mathematical model of the concomitant transmission of the two viruses suggests that HIV-1 will competitively displace HIV-2 in the longer term in areas where both viruses are being transmitted within the same sexually active population.