The spirochaetes

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The spirochaetes

• References
• Sherris p385-400
• Mandell et al p2117-2156

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Biology The Spirochaetes

• The order Spirochaetales are a group of bacteria
  characterised by a common morphology
• all are thin helical gram negative bacteria

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Biology The Spirochaetes

• The order has two families and seven genera, 3 of
  which are associated with human disease
• Treponema
• Borrelia
• Leptospira

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Biology type species T.pallidum

• T.pallidum var pallidum is the causative agent of
  the STD syphilis.
• The agent is strictly a human pathogen
• Is morphologically thin (too thin to be seen in a
  Gram stain)

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Ref http//www.telemedicine.org/156.HTM
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• Can only be cultured in vitro in live cells
  (even this is slow and poorly productive)
• Mostly cultured by rabbit inoculation eg rabbit
  testis
• Originally thought to be anaerobic -but has been
  shown to utilise glucose oxidatively

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Pathogenesis T.pallidum

• Acute and chronic infections
• Less common STD after the discovery of
  antibiotics,resurgence since the late 1980s
• Transmission is by direct contact with infectious
  mucotaneous lesions
• T.pallidum may be ingested by phagocytes but
  generally survive this
• Spontaneous remission may occur
• Tissue damage may occur as a result of host
  immune response to infection

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Pathogenesis T.pallidumClinical presentation

• Characteristically has 3 broad stages
• early
• latent
• Tertiary
• There is also a congenital form

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1. Early stage disease

• Characteristic lesions classified as primary or
  secondary
• Primary lesions
• average incubation period of 21 days (varies
  10-90 days)
• Usually occur at site of inoculation
• Initially seen as red papules and then erode
  usually into a single indurated chancre

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• Secondary lesions
• Patch hair loss
• rash
• muco cutaneous lesions
• lymphandenopathy
• plaques in genital and peri rectal areas which
  may be essentially asymptomatic but are highly
  infectious (termed Condyloma latum)
• Most patients enter a latent period and may have
  relapse w/i 4yrs

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Refhttp//www.telemedicine.org/DISEASES.HTM
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2. Latent Disease

• Also has early and late stages
• Early latency associated with relapse w/i 4years
• Late latency 4years before development of
  tertiary symptoms

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3. Tertiary syphilis

• About 1/3 untreated patients develop symptoms
  10-20 years after infection
• Mainly affects cardiovascular and nervous systems
• Granulomas (termed gummas) are non infectious and
  may form in any tissue

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4. Congenital syphilis

• Usually first detected as inflammation of
  umbilical cord (termed necrotising funisitis)
• Has variable clinical presentation but includes
• Rhinitis (sniffles)
• Macupapular desquamatous rash

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Diagnosis of syphilis

• Visual detection of bacterium by darkfield
  microscopy (and or silver stain)
• Serology (2 main tests)
• Treponeme non specific
• Treponeme specific

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Non-treponemal specific serology

• RPR (Rapid Plasma Reagin)
• VRDL (Venereal Disease Research Laboratory)

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• Both tests measure IgG and IgM antibodies which
  develop against lipids released from damaged
  cells especially early in infection (can also be
  present on treponeme surface)
• The Ag used is cardiolipin which flocculates when
  exposed to positive patient serum

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• Only the VDRL is useful in neurosyphilis
• Non treponemal tests often develop later and may
  be negative in early infection
• Good indicators of successful treatment as the
  titre drops quickly in these cases (cw long
  lasting treponemal specific tests)
• The specificity of these tests is about 98

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Treponemal specific serology

• FTA.abs (Fluorescent treponemal antibody
  absorbed)
• MHA-TP (microhaemagglutination assay to T.
  pallidum)
• 1/3 of patients with primary and late syphilis
  test with negative serology
• False ve tests are common but titres are
  generally low in these cases

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Complications

• Most serious problems in tertiary syphilis
• cardiavascular disease
• eg. aortic aneurysm
• neural sequealea
• aseptic meningitis
• general paresis

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Treatment

• Depends on stage of disease
• Partners should be screened and treated if
  required
• No vaccines, dependent on antibiotics
• Early latent (lt1 year)
• Penicillin G 2-4 million IU im once-
• Tetracycline
• Erythromycin 500mg oral QID 14 days Doxycycline
  100mg oral BD 30 days

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• Late stage disease(excluding neurosyphilis)
• Penicillin G 2-4 IU im weekly for 3 weeks.
• Penicillin allergic patients tetracycline,
  erythromycin or doxycycline for 30 days

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• Neurosyphilis
• penicillin G 2-4 million IU iv 4 hourly for 10
  days
• Congenital
• Penicillin G 500,000 IU iv or im BD for 7 days
  then TDS to complete 10-14 day course