Harvest mite infestation in Horses (Equis) | Vetlexicon
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Harvest mite infestation

ISSN 2398-2977


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

Introduction

  • Parasitic skin disease primarily affecting the distal limbs and muzzle.
  • Cause: Eutrombicula spp (US)/Trombicula spp (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.

Presenting signs

  • Erythematous and/or papular lesions on the distal limbs and muzzle or any body part coming into contact with infested hay or bedding.
  • Self-excoriation.

Geographic incidence

  • USA: widespread in America.
  • UK: east of Scotland and England, particularly in areas with chalky soil; rare in the west of Scotland.
  • Europe.
  • Australia.

Cost considerations

  • Cheap, medical treatment is effective.

Pathogenesis

Etiology

  • US: Eutrombicula alfreddugesi and E. splenden – the Chigger mite or Red bug.
  • UK and Europe: Trombicula autumnalis – the Harvest mite Trombicula spp or Heel bug.
  • Australia: Trombicula autumnalis and Trombicula sarcina – Blacksoil itch or Leg itch mite.

Pathophysiology

  • Adults live in pasture and woodland, especially with chalky soil, and feed on invertebrate hosts or plants.
  • Eggs are laid in damp areas and hatch in 1 week.
  • 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.
  • Infestation is more likely in pastured animals.

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.
  • Mair T S (1994) Headshaking associated with trombicula autumnalis larval infestation in two horses. Equine Vet J 26 (3), 244-245 PubMed.
  • Foil L (1986) Parasitic skin diseases. Vet Clin North Am Equine Pract (2), 403-427 PubMed.

Other sources of information

  • Scott D W & Miller W H (2011) Equine Dermatology. 2nd edn. Saunders, USA.
  • Knottenbelt D C (2009) Pascoe’s Principles and Practice of Equine Dermatology. 2nd edn. Saunders, USA.
  • 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.