Mucosal Transmission of Simian Immunodeficiency Virus

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Abstract

Although human immunodeficiency virus (HIV) is transmitted primarily by heterosexual contact very little is understood about the biology of heterosexual transmission of HIV. Epidemiological studies indicate that HIV is not efficiently transmitted by sexual contact. In fact many other sexually transmitted diseases (STDs) are more efficiently transmitted. For example, 22%–25% of individuals are infected by one exposure to Neisseriia gonorrheae (Holmes et al. 1970; Hooper et al. 1988), and hepatitis B virus is transmitted in 20%–30% of exposures (Judson 1981; Molsey 1975). In contrast, less than 15% of those monogamous individuals repeatedly exposed to an infected sexual partner become infected with HIV (Holmberg et al. 1989). It is estimated that for a single sexual contact, the infectivity of HIV is 0.3% (Hearst and Hulley 1988; Lawrence et al. 1990; Padian et al. 1987; Peterman et al. 1988). However, some individuals become infected after a single or a few sexual contacts (Peterman etal. 1988; Staskewski et al. 1987), while others remain uninfected despite hundreds of contacts (Lawrence et al. 1990). In the United States, HIV is apparently more efficiently transmitted from men to women than from women to men (Padian et al. 1987, 1991). Several cofactors have been identified which increase the risk of an individual acquiring HIV through heterosexual contact. Cervical ectopy, receptive anal intercourse, genital ulcer disease, and infection with other STDs are the most significant factors associated with HIV infection of women (Holmberg et al. 1988; Holmes and Kreiss 1988, Plummer et al. 1991) while the presence of an intact foreskin and genital ulcer disease of the penis are the risk factors most often associated with HIV infection in men (Cameron et al. 1989; Simonsen et al. 1988).