Equis ISSN 2398-2977

Harvest mite infestation

Synonym(s): Red bug infestation, Chigger mite infestation, Trombiculidiasis

Contributor(s): Sue Paterson, Craig Reinemeyer, David Senter

Introduction

  • Parasitic skin disease primarily affecting the distal limbs and muzzle.
  • Cause:Eutrombicula autumnalis(US)/Trombicula autumnalis(UK)   Trombicula spp  mite infestation and sensitivity.
  • Signs: pruritic and erythematous lesions on the distal limbs and muzzle.
  • Diagnosis: red/orange mites seen in the area of the lesions.
  • Treatment: ectoparasiticide washes/powders +/- symptomatic treatment of lesions.

Pathogenesis

Etiology

  • US:Eutrombiculaspp - the Chigger mite or Red bug.
  • UK:Trombicula autumnalis- the Harvest mite   Trombicula spp   or Heel bug.
  • Australia:Trombicula sarcina -Blacksoil itch or Leg itch mite.

Pathophysiology

  • Larvae normally parasitic on plants or insects are transferred to horses from forage, hay, bedding or grain.
  • Direct contact between horse and feed or bedding   →   infestation persists for a few days.
  • Mites on the skin surface insert mouthparts into superficial layers of skin   →   inject a cytolytic enzyme.
  • Partially digested tissue   →   local sensitivity response as horse become hypersensitive to the enzyme   →   inflammation, papule and vesicle formation, pruritus and self-excoriation   →   secondary bacterial infection.
  • Severity tends to increase with successive exposure as the horse becomes more sensitized.

Epidemiology

  • Occurs sporadically in late summer/autumn due to presence of mites.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Pilsworth R C & Knottenbelt D C (2005) Trombiculidiasis. Equine Vet J 17 (1), 9-10 VetMedResource.
  • Foil L (1986) Parasitic skin diseases. Vet Clin North Am Equine Pract (2), 403-427 PubMed.

Other sources of information

  • Rose R J & Hodgson D R (1993) Manual of Equine Practice. Saunders. ISBN: 0 7216 3739 6.
  • Urqhart G M, Armour J, Duncan J L et al (1988) Veterinary Parasitology. Longmann Scientific and Technical. ISBN: 0 5824 0906 3.


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