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Pathogenesis and Microbiology
The etiologic agent of syphilis is Treponema pallidum, subspecies pallidum. It is a corkscrew-shaped, motile
microaerophilic bacterium that cannot be cultured in vitro. It is thin (0.1-0.18 micrometers in diameter) and a bit longer than the diameter of a white blood cell (6-20 micrometers).
T. pallidum cannot be viewed by normal light
microscopy.
(Click on image for larger view)
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(Click on image for larger view)
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Penetration
T. pallidum enters the body via skin and mucous membranes through macroscopic
and microscopic abrasions during sexual contact. It may also be transmitted
transplacentally from mother to fetus during pregnancy.
Dissemination
Before clinical signs or symptoms appear, and within a few hours after inoculation, T. pallidum travels via the lymphatic system to regional lymph nodes and then throughout the body via the blood stream. Invasion of the central nervous system can occur during any stage of syphilis.
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