Equis ISSN 2398-2977

Borrelia burgdorferi

Synonym(s): B. burgdorferi, Lyme disease

Contributor(s): Susan Dawson, Richard Walker, Jamie Prutton

Introduction

Classification

Taxonomy

  • Family: Spirochetaceae.
  • Genus: Borrelia.
  • Species: burgdorferi.

Etymology

  • Genus name: named after the French bacteriologist Amédée Borrel (1867-1936).
  • Species epithet: named after Willy Burgdorfer.

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Clinical Effects

Epidemiology

Habitat

  • Reservoir in ixodes ticks (4%) and mammalian reservoirs such as rodents and birds. Deer act as a natural reservoir for ticks but do not appear to act as a host for the spirochete. 

Lifecycle for the Ixodes tick

  • Two year lifecycle.
  • Four distinct developmental stages and three hosts are required.
  • Tick larvae emerge in spring → infected by feeding on infected host.
  • Larvae drop off and enter resting stage until following spring → molt to nymphal stage.
  • Nymphs feed for 3-4 days on new host → host become infected with spirochetes.
  • Nymphs drop off and molt to adult stage.
  • Adults feed for 5-7 days on large mammals.
  • Females overwinter and lay eggs the following spring.

Transmission

  • Tick bite - Ixodes spp are the arthropod vectors; species depends on the geographical location, eg in the UK, the tick involved is Ixodes ricinus.
  • In the US, Ixodes scapularis and Ixodes pacificus the principle vectors.
  • Canine, feline and equine infections are not considered zoonotic as they are dead end hosts.

Pathological effects

  • Several hours of tick attachment are required to transfer the organism to the host.
  • OspA is downregulated within the organism to allow survival in the tick gut.
  • OspC is upregulated during transmission as are the variable major protein-like sequence expressed (VLsE) which are essential for acute and chronic infection.
  • OspF is upregulated for chronic infection.
  • Organisms spread locally through connective tissue then systemically through blood.
  • Clinical signs are not definitive as Koch’s postulates have not been fulfilled in the horse.
  • Neuroborreliosis: this has been confirmed with evidence of marked behavioral changes and ataxia.
  • Postulated clinical signs include: arthritis, uveitis, lethargy and behavioral changes.
  • Cutaneous pseudolymphoma has been reported at the site of attachment of the tick.

Control

Control via animal

  • Removal from tick areas can help.

Control via chemotherapies

  • No definitive protocol has been documented.  In humans multiple different regimes exist.
  • Tetracyclines are likely the best first line treatment. Oxytetracycline Oxytetracycline (5 mg/kg IV q24h), doxycycline (10 mg/kg PO q24h).
  • β-lactams can be used but appropriate antibiotic stewardship should be undertaken.  Ceftiofur Ceftiofur (2.2 mg/kg IM q24h).
  • Duration of treatment can vary from 2-4 weeks. Conversion to a seronegative state is not an appropriate goal as this can take months following clearing of the spirochete.
  • Non-steroidal anti-inflammatories are helpful if pain is suspected.

Control via environment

  • Chemical control of tick populations in endemic areas should be undertaken to reduce exposure to the ticks.
  • Rapid removal of ticks can reduce the transmission of the spirochete to the horse.

Vaccination

  • No vaccination is available.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Divers T J et al (2018) Borrelia burgdorferi Infection and Lyme Disease in North American Horses: A Consensus Statement. J Vet Int Med 32 (2), 617-632 PubMed.

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