Organism

Borrelia Burgdorferi (spirochaete)
Incubation: 7-14 days

Transmission

Vector=ticks
Animal hosts=deer/rodents

Epidemiology

Commonest vector borne illness in USA
Focally endemic in woodland of north America – infections mostly occur in summer.

Pathogenesis

  • Tick bite
  • B. burgdorferi is injected into the skin in tick saliva
  • This contains substances that disrupt the immune response at the bite site
  • Allows infection establish
  • The bacteria multiply in the dermis
  • Host inflammatory response causes circular EM lesion
  • Spirochaetes spread via the bloodstream.

The spirochetes may avoid the immune response by a form of molecular mimicry, causing a pathogen-induced auto-immune disease by causing inflammatory substances such as cytokines.

Clinical features

  • Early localized:
  • Skin reaction around bite site (erythema migrans)
  • Regional lymphadenopathy
  • Fever
  • Headache

Early disseminated

  • Arthralgia
  • Malaise
  • Pronounced systemic reaction
  • Carditis (sometimes with AV conduction defects)
  • Neurological involvement

Complications

  • Polyneuritis
  • Arthritis
  • Encephalopathy
  • Acrodematitis chronic atropicans

Diagnosis

Primarily clinical diagnosis, confirmed by antibody detection.
Culture from biopsy

Treatment

Doxycycline/amoxicillin (14 days, longer if disseminated)
IV cefotaxime in neurological disease

Prevention

  • Protective clothing/insect repellants
  • Special care in handling and allowing outdoor pets inside homes
  • Prompt remova of attatched ticks
  • Reduction in the number of primary hosts for the tick(i.e. rodents, other small mammals, and deer)

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