Cyathostomins

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)