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PH-IM07

Syphilis

How Treponema pallidum slips through skin or mucosa and spreads early, why plasma cells and obliterative endarteritis mark every stage, and how untreated infection can damage the aorta and nervous system years later.

By the end, you can

  • Explain how Treponema pallidum enters, spreads and evades the immune response.
  • Describe the chancre, the lesions of secondary syphilis and the gumma, and the endarteritis they share.
  • Explain how endarteritis of the vasa vasorum causes an aneurysm of the ascending aorta.
  • Relate the forms of neurosyphilis to the structures they damage.
  • Explain what treponemal and non-treponemal antibody tests detect.
  • Recognise the classic appearances, stages and tests of syphilis, explain why treponemal and non-treponemal tests are used together, and explain how penicillin acts on the infection.

What it is

Syphilis is a chronic infection by the spirochaete Treponema pallidum, spread mainly by sexual contact and across the placenta. Untreated, it passes through primary (chancre), secondary (body-wide spread) and latent stages; years later a minority develop tertiary disease of the skin and bones, the aorta or the nervous system. Neurosyphilis can occur at any stage.

3 types to tell apart
Early syphilis
Primary, secondary and early latent infection: lesions are infectious and relapses can occur. Guidelines set the end of the early period at one or two years after infection.
Late syphilis
Late latent and tertiary infection: few organisms, little sexual transmission, and damage driven largely by the immune reaction.
Congenital syphilis
Infection of the fetus across the placenta, most likely when the pregnant person has early syphilis.

Normal function

Skin, mucosa and small vessels

The stratified squamous epithelium of the skin and of the genital, anal and oral mucosa is a barrier: its layers of tightly joined cells keep bacteria out unless the surface is broken. Beneath it, the carries a fine network of , and lymphatics drain the tissue to the regional lymph nodes.

Small arteries have a thin intima lined by endothelium, a muscular media and an outer adventitia. The wall of a large artery such as the aorta is too thick to be fed from its lumen alone: tiny vessels of its own, the vasa vasorum, enter from the adventitia and supply its outer layers.

Most bacteria that breach the barrier are cleared within days by neutrophils, complement and antibodies, which bind proteins on the bacterial surface and mark it for destruction.

Point to it on the model