Heterosexual transmission of human immunodeficiency virus type 1 (HIV): interactions of conventional sexually transmitted diseases, hormonal contraception and HIV-1.

The interactions between HIV-1 and other viral sexually transmitted infections (STI) are complex. The presence of ulcerative and nonulcerative STD increase susceptibility of exposed individuals to HIV-1 infection by several folds. In HIV-1 infected individuals, STD increase genital tract shedding of HIV-1 and enhance the infectivity of these individuals. STD have also recently been shown to increase plasma viremia either directly or through altering the cytokine milieu, which may both increase infectivity and result in more rapid HIV-1 disease progression. HIV-1 infection in turn has effects on susceptibility to other STD as well as increasing the serverity of some infections and possibly reducing the response to antimicrobial therapy. In addition, other potential risk factors for sexual transmission of HIV-1, such as hormonal contraception in women and lack of circumcision in men, may operate partly through effects on enhancing susceptibility to STD. The mutual enhancement of transmission of HIV-1 and other STD that has fueled HIV-1 epidemics worldwide, offers the opportunity for intervention. The effectiveness of this approach has recently been demonstrated in a trial in Mwanza, Tanzania, where provision of effective treatment for STD resulted in a 40% decline in HIV-1 incidence. The implementation of effective STD management may do much to slow the spread of HIV-1.