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Treponema pallidum / Syphilis

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Topic updated on 04/09/14 2:18pm

Introduction
  • Classification
    • Bacteria
      • other bacteria
        • Spirochetes
          • Treponema
            • T. pallidum
  • Pathogenesis
    • transmission
      • sex
      • across the placenta
    • reservoir
      • GU tract
    • molecular biology
      • obligate pathogen
        • not intracellular
Diseases
  • Syphilis (3 stages + congenital) 
    • primary syphilis
      • painless chancre 
        • due to ischemic necrosis
      • indurated edge
      • diagnose with dark-field or fluorescent microscopy of lesion at this stage
    • secondary syphilis
      • "secondary is systemic"
      • diffuse copper-colored maculopapular rash
      • condylomata lata
        • wartlike lesions in perianal area
        • highly infectious with many treponemes present
      • diagnose with VDRL or FTA-ABS at this stage
    • tertiary syphilis
      • gummas
        • granulomatous lesions of skin and bones
      • aortitis (vasa vasorum destruction)
      • neurosyphilis (e.g. tabes dorsalis)
      • Argyll-Robertson pupil
        • "prostitutes pupil"
          • "accommodates but does not react" (to light)
      • diagnose with FTA-ABS at this stage
    • congenital syphilis
      • stillbirth or hydrops fetalis
      • neurosyphilis (CN VIII deafness)
      • bone and teeth abnormalities
        • saddle nose (sunken appearance)
        • saber shins (bowing of tibia)
        • Hutchinson's teeth (notches in teeth with wide spacing between them)
        • mulberry molars (too many cusps on molars)
    • note that 3 different cutaneous lesions may occur during the 3 stages
      • 1 - chancre
      • 2 - condyloma lata
      • 3 - gumma
    • pathophysiology
      • all of syphilis is a vasculitis
        • Treponema infects
          • small vessels and arterioles
          • aortic arch
            • rich vasa vasorum
            • can lead to aortic regurgitation due to stretching of ring around aortic valve
Laboratory
  • Visualized using dark-field microscopy or fluorescent antibodies
    • reveals motile, helical organisms
  • Thin spirochete
    • although Gram-negative, not visualized on Gram-stain
Diagnostic tests for syphilis
  • 2 types of screening tests are used to diagnose syphilis infection
    • VDRL (non-specific test) (note: RPR, or rapid plasma reagin, test is newer but very similar)
      • infection with syphilis results in cellular damage and release of specific lipids into the bloodstream, including cardiolipin
      • the body then produces antibodies against cardiolipin
        • cardiolipin is a glycerophospholipid also known as diphosphatidylglycerol
        • component of inner mitochondrial membrane and bacterial membranes
        • cardiolipin is the only antigenic human glycerophospholipid
      • Venereal Disease Research Laboratory (VDRL) test measures levels of these anti-cardiolipin antibodies using beef cardiolipin
        • note that test is looking for antibodies against a human cellular lipid, not antibodies against Treponema
      • VDRL becomes negative as disease is successfully treated
      • 1% of adults will have a false-positive VDRL
        • remember "VDRL" for causes of false-positives
          • Viruses (e.g. hepatitis)
          • Drugs
          • Rheumatic fever
          • Lupus and Leprosy
    • FTA-ABS (specific test)
      • Treponemal Antibody-Absorption test (FTA-ABS) looks for antibodies against the spirochete itself
        • indirect immunofluorescence of patient serum mixed with whole, killed Treponema pallidum
      • ↑ specificity
      • positive earlier and remains positive for life
      • "ABS will ABSolutely detect the antibodies"
VDRL
FTA
Interpretation
+
+
Active infection
+
-
Probably false positive
-
+
Successfully treated
  • Note that Treponema pertenue also causes a VDRL positive result
    • T. pertenue causes the disease yaws
      • infection of bone, joints, and skin
      • keloids during healing lead to severe limb deformities
      • most prevalent in the tropics
      • not an STD
Treatment
  • Benzathine penicillin for primary and secondary disease
  • Penicillin G for congenital and late disease


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