Small strongyles (Cyathostomins)

Morphology

Gross:

  • Small worms, <1.5cm long
  • Small, shallow buccal capsule

Microscopic:

  • Buccal capsule shape
  • Double row of leaf crowns
  • Teeth may be present

Life-cycle

  • Infection by ingestion of L3
  • Larvae invade mucosa of large intestine
  • Larvae may develop to L4 without interruption
  • Cyathostomin larvae can arrest at EL3 stage
  • L4 emerge into gut lumen and mature to adult worms
  • Prepatent period 8-12 weeks (depending on species)

Pathogenicity

General:

  • Adult and larval worms are plug feeders, restricting the damage to more superficial mucosa

Cyathostominosis:

  • Initial infection (L3) → local inflammatory response
  • Developing L4s can be seen as brown flecks in the mucosa
  • They can be present in very large numbers (→ the so-called "pepper-pot lesion")
  • Larval emergence throughout summer/autumn and plug-feeding of adults → major contributor to the "wormy" horse:
    • Unthriftiness
    • Poor coat
    • Anaemia
    • Diarrhoea)
  • May be tens or hundreds of thousands of adults and millions of mucosal larvae present
  • Emergence of massive numbers of previously arrested larvae in late winter/early spring → massive inflammatory infiltration → serious disease characterised by severe diarrhoea and/or weight loss (larval or Type 2 cyathostominosis)