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)