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Syphilis is a complex infectious disease caused by Treponema pallidum, a spirochete capable of infecting almost any organ or tissue in the body and causing protean clinical manifestations (Table 34–1). Transmission occurs most frequently during sexual contact (including oral sex). The risk of acquiring syphilis after unprotected sex with an individual with infectious syphilis is approximately 30–50%. Rarely, it can also be transmitted through nonsexual contact, blood transfusion, or via the placenta from mother to fetus (congenital syphilis). The immunologic response to infection is complex, but it provides the basis for most clinical diagnoses. The infection induces the synthesis of a number of antibodies, some of which react specifically with pathogenic treponemes and some with components of normal tissues (see below). If the disease is untreated, in most cases these immune reactions fail to eradicate existing infection and may contribute to tissue degeneration in the late stages. Patients treated early in the disease are fully susceptible to reinfection.

Table 34–1.Stages of syphilis and common clinical manifestations.

The natural history of acquired syphilis is generally divided into two major stages: early (infectious) syphilis and late syphilis. Infectious syphilis includes primary lesions (chancre and regional lymphadenopathy) appearing during primary syphilis, secondary lesions (commonly involving skin and mucous membranes, occasionally bone, central nervous system [CNS], or liver) appearing during secondary syphilis (when dissemination of T pallidum produces systemic signs), relapsing lesions during early latency, and congenital lesions. The hallmark of these lesions is an abundance of spirochetes; tissue reaction is usually minimal. Late (tertiary) syphilis consists of so-called benign (gummatous) lesions involving skin, bones, and viscera; cardiovascular disease (principally aortitis); and a variety of CNS and ocular syndromes. These forms of syphilis are not contagious. The lesions contain few demonstrable spirochetes, but tissue reactivity (vasculitis, necrosis) is severe and suggestive of hypersensitivity phenomena. Between these stages are symptom-free latent phases. In early latent syphilis, which is defined as the symptom-free interval lasting up to 1 year after ...

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