Pathogenesis

Like the spirochetes that cause leptospirosis, T. pallidum readily penetrates mucous membranes and abraded skin. The infectious dose is very low, less than 100 organisms. In primary syphilis, T. pallidum grows and multiplies in a localized area of the genitalia, spreading from there to the lymph nodes and bloodstream. The hard chancre represents an intense inflammatory response to the bacterial invasion. Sometimes no chancre develops, only a pimple small enough to go unnoticed. Examination of a drop of fluid squeezed from the chancre reveals that it is teeming with infectious T. pallidum. Whether or not treatment is given, the chancre disappears within 2 to 6 weeks, and the victim may mistakenly believe that recovery from the disease has occurred. The organisms resist destruction by the body's defenses by an unknown mechanism, however, and progression of the disease can continue for years.

Figure 25.11 Syphilitic Chancre on the Foreskin of an Uncircumcised

Man This is the site where Treponema pallidum entered the man's body.

Figure 25.11 Syphilitic Chancre on the Foreskin of an Uncircumcised

Man This is the site where Treponema pallidum entered the man's body.

5 mm

Figure 25.12 Appearance of Treponema pallidum with Dark-Field Illumination This technique readily detects the organism in skin and mucous membrane lesions of syphilis.

Nester-Anderson-Roberts: IV. Infectious Diseases 25. Genitourinary © The McGraw-Hill

Microbiology, A Human Infections Companies, 2003

Perspective, Fourth Edition

Chapter 25 Genitourinary Infections

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