Lyme Disease
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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)

References

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) currently works as a GP Registrar and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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