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Endoparasites - Strongyloides

        Strongyloides papillosus: Intestinal threadworm.

General Description: Small, thread-like adults are up to 6mm long. Only females are parasitic.

Life Cycle: Life cycle contains two types of adults, parasitic and free-living. Parasitic females in the intestine are parthenogenetic (the eggs laid by them hatch and develop without fertilisation). Hatched larvae may develop to become infective third-stage larvae which enter animals through ingestion or through skin penetration and become parasitic female worms (homogonic cycle). Hatched larvae, in the heterogonic cycle, develop into free-living male and female adults which grow and mate on pasture, producing eggs that become female infective third-stage larvae. Infective larvae, produced from either cycle, have a prepatent period of 7 to 9 days after entering the sheep by skin penetration.

Location: Small intestine.

Geographical Distribution: Worldwide, especially in warm, humid areas.

Significance: Intestinal threadworms damage sheep in several ways and make sheep raising unprofitable in areas of high worm infection.

Effect on Host: Adults cause erosion of the intestinal lining; diarrhoea, which may be bloody, can follow. This persists and wasting occurs because sheep lose their appetite. Death may follow. Skin penetration causes dermatitis which results in intense itching, especially of feet. Damage incurred by penetrating larvae may predispose sheep to foot rot.

Diagnostic Information: Small, thin-shelled eggs containing larvae appear in faeces.

Control: Prevention should include administration of anthelmintics and attempts to keep sheep areas dry and clean. Avoid overcrowding.

 
Threadworm   Strongyloides eggs
     
 
Consolidation caused by larvae migration in lungs   Larvae under skin

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