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

• Strongyloides westerithe equine threadworm   Strongyloides westeri        .

Predisposing factors

• 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

Treatment

Prevention

Outcomes