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
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.