THE ROLE OF CO-INFECTION IN THE SPREAD OF HIV IN SUB-SAHARAN AFRICA

The cause of the high HIV prevalence in sub-Saharan Africa is incompletely understood, with heterosexual penile-vaginal transmission proposed as the main mechanism. Heterosexual HIV transmission has a very low probability; further, a single estimation of heterosexual probability of HIV transmission fails to reproduce the variation associated with important biological cofactors. In particular, studies of HIV incidence suggest that co-infection with other infectious diseases influence the HIV transmission, and therefore might substantially vary the pattern of the spread of the infection. To assess the effect of co-infection on the spread of HIV, I developed and analyzed several mathematical and statistical models based on published data. The results show that despite the low probability of heterosexual transmission per sexual contact, the inclusion of individual variation generated by transient but repeated increases in HIV viral load associated with co-infections may provide a biological basis for the accelerated spread of HIV in sub-Saharan Africa, and raises the possibility that that the natural history of HIV in sub-Saharan Africa cannot be fully understood if individual variation in infectiousness is neglected. Co-infection might be a key explanatory variable for the rapid spread of HIV infection in sub-Saharan Africa; in fact, co-infection may be a necessary factor, rather than merely being a contributing factor, in the successful spread and survival of HIV in populations where heterosexual vaginal-penile contact is the main mechanism of transmission. Consequently, broad population based control strategies to decrease infectivity and reduce the incidence of other sexual and parasitic infectious diseases might be effective strategies in diminishing the spread of HIV in sub-Saharan Africa