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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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Qbank (1 Questions)

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0) (M1.MC.6) A 51-year-old man presents complaining of decreased vibratory sense in his lower limbs. Physical exam reveals a widened pulse pressure and a decrescendo murmur occurring after the S2 heart sound. After further questioning, he also reports he experienced a maculopapular rash over his trunk, palms and soles many years ago that resolved on its own. In order to evaluate the suspected diagnosis, the physician FIRST tested for which of the following? Topic Review Topic

1. Agglutination of antibodies with beef cardiolipin
2. Indirect immunofluoresence of the patient’s serum and killed T. palladium
3. Cytoplasmic inclusions on Giemsa stain
4. Agglutination of patients serum with Proteus O antigens
5. Gram positive, oxidase positive, comma shaped bacteria growing at 42 degrees C

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