Category:Sheep Nematodes

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Nematodes of Sheep - Gastrointestinal Nematodes

Nematodirus from ruminant faeces - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona

Many worm species occur in the gastrointestinal tract of sheep, though relatively few are of importance in the UK. Primary pathogens include:

Abomasum Small Intestine Large Intestine
Primary Pathogens in the UK
  • Haemonchus contortus
  • Trichostrongylus species
  • Nematodirus battus
Worms that contribute to ovine PGE, but are rarely primary pathogens in the UK
  • Trichostrongylus axei
  • other Nematodirus species
  • Cooperia species
  • Bunostomum species
  • Strongyloides species
  • Oesophagostomum species
  • Chabertia species
  • Trichuris species


  • All the above worms belong to the Trichotrongyloidea except:
    • Bunostomum (a hookworm)
    • Oesophagostomum
    • Chabertia (Strongyloidea)
    • Strongyloides (Rhabditoidea)
    • Trichuris (a whipworm)
  • Although many different genera and species of worms may be found in the gastro-intestinal tract of sheep there are only three distinct disease manifestations within the PGE complex:
    • Ostertagiosis and Trichostrongylosis
    • Nematodirosis
    • Haemonchosis

Succession of Gastrointestinal Worm Species

The relative number of worms of each species changes during the grazing season. The succession of species is due to differences in:

  • Ability of L3 to overwinter
  • Fecundity between worm species
  • Rate of development from egg to L3 stage
  • Special requirements of Nematodirus