Large Strongyles

Large strongyles

Morphology

Gross

• Stout worms, 1.5-5cm long
• Large buccal capsule
• Bursa visible to the naked eye (male worms only)

Microscopic (buccal capsule)

• Double row of leaf crowns
• Teeth (0, 2, 3 or more)
• Dorsal gutter (channel for secretions)

Life-cycle

Infection with all three Strongylus species and Triodontophorus is by ingestion of infective stage larvae (L3) at grazing. Larvae pass down the intestinal tract and penetrate the intestinal mucosa at which point there are important species differences in life-cycle.

Pathogenicity

Adult Worms:

• Plug feeders
• Strongylus species:
  • Large buccal capsule
  • Penetrate right down to the muscularis layer and blood vessels
  • Leaves small circular bleeding ulcers → anaemia if present in large numbers
• Triodontophorus:
  • Smaller buccal capsule
  • More superficial damage
  • May feed in "herds", leaving large ulcers, several centimetres across
• Ulcers heal and leave scars

Pathogenesis of infection with Strongylus species larvae:

• S. vulgaris:
  • Potentially highly pathogenic
  • Damage to cranial mesenteric artery → endarteritis → thrombosis and possibly embolism → colic
• Other Strongylus species :
  • Relatively non-pathogenic
  • Migration of S. edentatus and S. equinus confined to roomy tissues (e.g. mesentery, liver)