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.

Identification

They are small worms, generally less than 1.5cm long. They also have a distinctive, small buccal capsule. They also have two rows of leaf crowns, both internal and external.

The species range in colour from white to dark red.

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.

Encysted, or hypobiotic larvae are unaffected by Anthelmintic Drugs. These encysted larvae represent around 50% of the total population. After emergence of the cyst, L4 transforms into L5. They then transform into adults in the lumen.

If hypobiosis does not occur, the prepatent period is 6-14 weeks.

Highest egg shedding is in the Spring months. The larvae, which represent 90% of the population, are at maximal levels in the autumn.

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)