Equis ISSN 2398-2977

Strongyloides westeri infection

Contributor(s): Roberta Baxter, Joseph DiPietro, Sheelagh Lloyd

Introduction

  • Endoparasitic disease of horses.
  • Cause:Strongyloides westeri  Strongyloides westeri  , the equine threadworm.
  • Signs: diarrhea in young foals.
  • Diagnosis: clinical signs and presence ofStrongyloides westerieggs in feces.
  • Treatment: ivermectin   Ivermectin  , and benzimidazoles at high doses.
  • Prognosis: good.

Pathogenesis

Etiology

Predisposing factors

General
  • Age - horses develop age-related resistance to disease.
  • Immunosuppression.

Pathophysiology

  • Foals generally infected via dam's milk, but percutaneous infection can also occur   →   threadworms in small intestine   →   diarrhea.
  • Reservoir of larve in mare's tissue release larve which are triggered to migrate to the mammary glands during late pregnancy and lactation, and thus pass to the foal in milk.
  • Alternatively, worms can penetrate the skin causing local erythema, and thus gain access to the body before migrating to the intestine.
  • Aberrent migration via the lungs can occur with multiple small vesicles visible over the surface of the lungs; these rarely cause overt respiratory signs.
  • In the foal they develop into mature threadworms in the small intestine (where only the female worms are parasitic).
  • Here they cause catarrhal lesions with edema and erosions of the mucosal epithelium   →   impairment of digestion and absorption   →   diarrhea.
  • Eggs are passed in feces.
  • One or several free-living   Free-living nematodes    Free-living nematode 01: rhabditiform esophagus  generations may occur before a third stage infective larvae is produced.
  • The pathology is due to worms causing inflammation of the anterior third of the small intestine with villous atrophy and increased numbers of lymphocytes in the lamina propria.

Timecourse

  • The pre-patent period is 8-15 days.
  • Eggs have been found in the feces of foals within 2 weeks of experimental infection.

Epidemiology

  • The lifecycle is direct - no intermediate host is involved.
  • Free-living larval stages take varying times to produce infective L3.
  • Arrestation of larve occurs in the dam.
  • Larve develop and cause disease in the foal.

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.
  • Molento M B, Antunes J, Bentes R N & Coles G C (2008)Anthelmintic resistant nematodes in Brazilian horses.Vet Rec162(12), 384-385PubMed.
  • Morgan E R, Hetzel N, Povah C & Coles G C (2004)Prevalence and diagnosis of parasites of the stomach and small intestine in horses in south-west England.Vet Rec156(19), 597-600PubMed.
  • Kaplan R M & Little S E (2000)Controlling equine cyathostomes.Comp Cont Educ Pract Vet22(4), 391-395VetMedResource.
  • Lind O E, Hoglund J, Liungstrom B L, Nilsonn O & Uggla A (1999)A field study on the distribution of strongyle infections of horses in Sweden and factors affecting fecal egg counts.Equine Vet J31(1), 68-72PubMed.
  • Proudman C J (1999)The role in parasites in equine colic.Equine Vet Educ11(4), 219-224VetMedResource.
  • Craven J, Bjorn, Henriksen S A, Nansen P, Larsen M & Lendal S (1998)Survey of anthelmintic resistance on Danish horse farms, using 5 different methods of calculating fecal egg count reduction.Equine Vet J30(4), 289-293PubMed.
  • Rolfe P F, Dawson K L & Holm-Martin M (1998)Efficacy of moxidectin and other anthelminics against small strongyles in horses.Aust Vet J76(5), 332-334PubMed.

Other sources of information

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


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