Cyathostomins

Introduction

Cyathostomins are a group of small strongyles. The majority of cyathostomins are similar in terms of both morphology and behaviour. There are over 50 different species of small equine strongyle, and they are of huge significance throughout the United Kingdom. They commonly cause severe acute diarrhoea and colic.

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

L1-L3 occurs within the envelope. The L3 then exits the sheath in the small intestine, and then concentrates within the Lieberkuhn's gland. At this stage they are known as EL3, and have two potential options. Firstly, they may either become hypobiotic, remaining dormant for several months to years. This usually occurs Autumn-Winter. Or they may evolve directly and emerge 8-10 weeks later as LL3. They will then evolve into L4, at which stage they will emerge from a nodule.

• 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)