Treponema pallidum pallidum

Background

• Causes syphilis

Microbiology

• Small, slow-growing spirochete
• Not seen on standard microscopy; requires darkfield microscopy

Clinical Presentation

Stages

• Primary syphilis (incubation period 3 weeks [range 3 to 90 days])
• Secondary syphilis (incubation period 2 weeks to 3 months [range 2 weeks to 6 months])
• Latent
  • Early latent (<1 year)
  • Late latent (≥1 year)
• Tertiary syphilis (incubation period years to decades)
  • Cardiovascular (incubation period 10 to 30 years)
  • Gummatous (incubation period 15 years [range 1 to 46 years])
  • Neurosyphilis (incubation period 2 to 20 years)
    • Meningovascular
    • Parenchymatous
    • Tabes dorsalis
• Congenital
  • Early (< 2 years)
  • Late (≥ 2 years)

Primary syphilis

• Incubation period is about 3 weeks
• Chancre
• Ulcerative lesion
  • Clean borders
  • Indurated
  • Not painful unless secondarily infected
  • Lasts 2 to 6 weeks
• May present with regional lymphadenopathy
• Diagnosis with darkfield microscopy, fluorescent antibody smear, or (most commonly) serology
• Serology often negative in early syphilis

Secondary syphilis

• Incubation period 3 weeks to 3 months
• Often no history of chancre
• Diffuse maculopapular rash that involves palms and soles
  • Typically begins on trunk
  • Start as pinkish-reddish macular lesions that evolve into brownish-reddish papules that may have scaling
  • May progress to pustular lesions (pustular syphilids)
  • May be itchy
  • Can be isolated to palms and soles
• Generalized lymphadenopathy
• Fever, chills, arthralgias
• Less common: condyloma lata, aseptic meningitis, iritis, mucosal white patches, glomerulonephritis, paroxysmal nocturnal hemoglobinuria, hepatitis

Latent syphilis

• High rate of relapse of secondary syphilis within the first 1-2 years following infection (but especially within the first year)

Tertiary syphilis

• Eventually occurs in about 30% of untreated cases

Neurosyphilis

• Of the 25-60% of people who have CNS invasion, 95% are asymptomatic during the early stage and 80% of those spontaneously clear it
• Incubation period is 7-15 years
• Three major presentations: meningovascular syphilis, parenchymous syphilis, and tabse dorsalis

Meningovascular

• Possibly the most common neurosyphilis
• Subdivided into cerebromeningeal (diffuse or focal) and cerebrovascular
• Stroke-like symptoms, especially MCA or basilar territory
• Can present as a sudden change, as syphilitic apoplexy
• Can present following a prodrome of weeks to months of non-specific headaches, vertigo, irritability, insomnia, and personality changes

Parenchymatous

• Previously known as "generalized paresis of the insane"
• Occurs in 2-5% of cases of untreated syphilis
• Commonly found on psychiatric wards
• Causes psychosis and dementia
• Later, coarse tremors, Argyll-Robinson pupil, paresis

Tabes dorsalis

• Occurs in 2-9% of cases of untreated syphilis
• Isolated posterior cord degeneration leading to a loss of proprioception in the lower extremities
• Stomp the ground when walking to use intact pain/pressure sensation
• Loss of sensation in the Hitzig zones (tip of nose, band including nipple area, medial forearms, and lateral leg)
• Can present with Charcot foot and, rarely, recurrent abdominal pain
• Diagnosed by serum CMIA, but RPR may be negative

Others

• Isolated ocular neurosyphilis
• Meningitis: can present at any time during the course of disease
• Others

Cardiovascular syphilis

• Occurs in 10% of people with untreated syphilis
• Incubation period is 20-25 years
• Aortic root involvement leading to aortitis and dilatation
• May result in aneurysm, aortic insufficiency, or angina secondary to stenosis at the aortic root
• Diagnosed by RPR +/- CMIA

Gummatous syphilis

• Gummas are necrotizing granulomatous lesions
• Occurs in 15% of people with untreated syphilis
• Incubation period 6-8 years
• Gummas may appear anywhere, in any organ, but most commonly on the skin, on mucosa, and in bones
• CNS lesions look like toxo, so beware in HIV patients

Other presentations

• Isolated auditory syphilis
• Isolated optic syphilis

Diagnosis

• Often done as non-treponemal test to screen, followed by treponemal test to confirm
• In Ontario, we do a treponemal test to screen (CMIA), then repeat it with a more specific treponemal test (TPPA) alongside RPR

Direct visualization

• Darkfield microscopy
  • Chancre cleaned and smear obtained
  • Smear must be visualized immediately
  • Sensitivity decreases with duration
• Smear for fluorescent monoclonal antibody
  • Best to use in primary syphilis

Non-treponemal tests (VDRL/RPR)

• Veneral Diseases Research Laboratory (VDRL) has been replaced by the rapid plasma reagin (RPR) test
  • Quantitative tests for a non-specific anti-cardiolipin antibody that is produced in syphilitic (and other) infections
• False positives:
  • Acute biologic false positive: malaria, brucellosis, and mononucleosis; maybe pregnancy
  • Chronic biologic false positive: lupus and other autoimmune disorders, HIV, intravenous drug use, and leprosy
• Only 50% sensitive in primary, 100% sensitive in secondary
• Tests will eventually become nonreactive

Treponemal tests

• More specific and sensitive, but more expensive
• False positives: lupus and other autoimmune disorders, Lyme disease, and other treponemal infections
• Remain positive for life
• Four main tests:
  • Fluorescent treponemal antibody absorption (FTA-Abs): Essentially the gold standard
  • Chemoluminescnence microparticle immunoassay (CMIA or CLIA): the screening test used in Ontario. Often used as a screening test as it is an easily-automated immunoassay and is more sensitive and specific than RPR.
  • Treponema pallidum Particulate Agglutination assay (TPPA): a modification of the TPHA. Used as the confirmatory test (alongside RPR) used in Ontario.
  • T. pallidum hemagglutination assay (TPHA): very old test.
  • T. pallidum enzyme immunassay (TP-EIA)

Interpretation of serology

CMIA screen	RPR	TPPA	Interpretation
Non-reactive	—	—	Negative result; or early syphilis (consider repeat in 4 weeks)
Reactive	Reactive	Reactive	Recent or prior syphilis infection
Reactive	Non-reactive	Reactive	Recent or prior syphilis infection
Reactive	Non-reactive	Non-reactive	False positive; or early syphilis, previously treated, or late latent (repeat in 4 weeks)
Reactive	Non-reactive	Indeterminate	Inconclusive result; false positive, early syphilis, old treated syphilis, or old untreated syphilis (repeat in 4 weeks)
Reactive	Reactive	Non-reactive	Inconclusive result; false positive, early syphilis, old treated syphilis, or untreated syphilis (repeat in 4 weeks)
Reactive	Reactive	Indeterminate	Recent or prior syphilis infection

Treatment

Primary, secondary, and early latent

• Benzathine penicillin G 2.4 million units IM once, divided between two buttocks
• Alternative (penicillin allergy): doxycycline 100mg BID for 2 weeks
• Alternative (penicillin allergy and pregnancy): penicillin desensitization or azithromycin

Late latent and tertiary (excluding neurosyphilis)

• Benzathine penicillin G 2.4 million units IM q1week for 3 weeks
• Alternative (penicillin allergy): doxycycline for 30 days
• Monitor response with RPR titres, which should drop 4-fold within 6 months

Tertiary neurosyphilis

• Penicillin G 4 million units IV q4h for 10 to 14 days
• Often followed by at least one dose of IM benzathine penicillin, sometimes weekly for 2-3 weeks

Congenital syphilis

• If <1 month of age: crystalline penicillin G 50 kU/kg IV q12h for the first week of life and q8h thereafter, for a total of 10 days
• If ≥1 month of age: crystalline penicillin G 50,000 units/kg IV every 6 hours for 10-14 days
  • If there is no neurological involvement, then you can consider benzathine penicillin G 50 kU/kg (max 2.4 MU) IM weekly for 3 weeks

Further Reading

• Toronto Public Health Syphilis Laboratory Interpretation and Treatment (2-page PDF)