Equis ISSN 2398-2977

Stomach: gasterophilus infestation

Synonym(s): Bots, bot flies

Contributor(s): Sheelagh Lloyd

Introduction

  • Gasterophiluscauses a parasitic condition of horses but is rarely pathogenic.
  • Cause:Gasterophiluseggs   Gasterophilus  are laid on the hair of the horse; the larvae develop in the horse's stomach and mouth.
  • Although the presence of the larvae in the stomach rarely causes disease, the adult fly may cause annoyance as it lays eggs. Most horses tolerate it.
  • Treatment: and control involve the use of boticides or removal of eggs.

Pathogenesis

Etiology

  • Gasterophilusspp   Gasterophilus  .
  • Gasterophilus intestinalis- cream, yellow eggs are laid on the forelegs, shoulders, mane and abdomen   Gasterophilus: eggs    →   reddish larvae mature in the cardiac region of the stomach.
  • Gasterophilus nasalis- yellow eggs are laid in the throat area   →   develop in the pyloric area of the stomach and the duodenum.
  • Gasterophilus hemorrhoidalis- dark brown eggs are laid around the mouth   →   develop in the fundus of the stomach, duodenum and attach briefly to rectum.

Pathophysiology

  • Gasterophilusflies cause annoyance as they lay eggs on horse's hair   →   horse grooms eggs on hairs or larvae hatch spontaneously   →   larvae hatch, penetrate oral mucosa and travel to stomach   →   develop and pass into feces   →   develop into adult fly.
  • Large bee-like flies   Gasterophilus intestinalis: female fly  may annoy the horse, particularlyG. nasalisandG. hemorrhoidaliswhich cluster around the head area.
  • Eggs are laid   →   horse grooms area.
  • Increase in moisture and temperature in the mouth, and action of the horse's lips cause hatching of the eggs (G. intestinalis). Alternatively, eggs can hatch automatically after 5 days and larvae then crawl to the mouth (G. nasalis,G. hemorrhoidalis).
  • Larvae burrow into tongue and lodge between the upper cheek teeth and can cause mild stomatitis   Vesicular stomatitis  .
  • Larvae then are released and travel to relevant area of stomach and proximal small intestine to develop.
  • Here they can cause deep, fibrous pits in the mucosa, ulceration has even been seen, but rare.
  • Larvae are passed in feces and pupate for 1-2 months on pasture.
  • Large numbers ofG. intestinalislarvae in colon can cause tenesmus, very rare.

Epidemiology

  • The life-cycle is direct - no intermediate host is involved.
  • One generation of life-cycle occurs each year.
  • Flies are active and laying eggs during warmer weather.
  • Larvae spend 9-10 months developing in stomach and proximal small intestine.
  • Larvae are passed the following year in early summer in feces to pupate and hatch into adult flies.

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.
  • Coles G C & Pearson G R (2000) Gasterophilus nasalis infection - prevalence and pathological changes in equids in south-west England. Vet Rec 146 (8), 222-223 VetMedResource.
  • Lloyd S et al (2000) Parasite control methods used by horse owners predisposing to the development of anthelmintic resistance in nematodes. Vet Rec 146, 487-492 VetMedResource.
  • Cogley T P & Cogley M C (1999) Inter-relationship between Gasterophilus larvae and the horse's gastric and duodenal wall with special reference to penetration. Vet Parasiol 86 (2), 127-142 PubMed.
  • Agneessens J, Engelen S, Debever P & Vercruysse J (1998) Gasterophilus intestinalis infections in horses in Belgium. Vet Parasitol 77 (2-3), 199-204 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, Dunn A M & Jennings F W (1988) Veterinary Parasitology. Longmann Scientific and Technical. ISBN 0 5824 0906 3.


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