Alterations in the course of experimental syphilis associated with concurrent simian immunodeficiency virus infection

Case reports suggest that the course of syphilis is altered in patients infected with human immunodeficiency virus (HIV). To investigate this issue, a model of syphilis in rhesus macaques with and without simian immunodeficiency virus (SIV) was developed. After intradermal inoculation with Treponema pallidum, 2 SIV-infected monkeys had persistent ulcerative primary lesions and 1 developed secondary syphilis. Two SIV-uninfected controls developed transient nonulcerative primary lesions. Only the controls showed consistent VDRL antibody responses. In contrast, reciprocal antibody titers to T. pallidum detected by microhemagglutination were higher in SIV-infected animals (greater than or equal to 20,480) than controls (greater than or equal to 1280). All 4 animals developed a full range of T. pallidum antigen-specific antibodies shown by immunoblot and had similar peak lymphocyte proliferative responses to T. pallidum antigens. These results support the contention that retrovirus-induced immunodeficiency delays clearance of T. pallidum from sites of infection and may impair the humoral immune response to syphilis.