What is Cyathostominosis:
Cyathostominosis is a serious condition in horses that occurs when large numbers of encysted larvae of the small redworm (cyathostominae) suddenly emerge from the intestinal wall. This mass emergence triggers a severe inflammatory reaction in the large intestine, potentially leading to life-threatening symptoms.

How does cyathostominosis develop?
Small redworms are the most common worm species in horses. Part of their life cycle takes place inside the intestinal wall:

• Larvae are ingested during grazing.
• They encyst in the intestinal wall (larval arrest).
• They can remain inactive for months or even years.
• Under certain conditions, large numbers of larvae emerge simultaneously from the intestinal wall.

When this happens, the intestinal wall becomes severely inflamed in a short period of time. This is cyathostominosis.

Symptoms of cyathostominosis:
The associated symptoms are often acute and severe:

• (Severe) diarrhoea
• Rapid weight loss
• Dull or rough coat
• Bloated abdomen
• Lethargy, dullness, reduced appetite
• Fever (sometimes, but not always)
• Oedema (underbelly or legs)
• Sometimes signs of colic
  Without timely treatment, cyathostominosis can in some cases become life-threatening.

Can cyathostominosis be detected via a fecal test?
No – encysted larvae cannot be seen in a fecal test.
A fecal test may therefore be negative even when the horse carries many encysted larvae.

A positive fecal test reflects active egg-shedding worms, not the number of encysted larvae.

This is why a proper annual plan, including record-keeping and seasonal advice, is so important.

Treatment:
Cyathostominosis is a condition that always requires veterinary involvement. Treatment often includes:

• Anti-inflammatory medication
• Fluid and electrolyte support
• Deworming if appropriate for the situation
• Intensive monitoring
• Additional supportive care such as mash, gut-repair supplements, and regular checks

Can cyathostominosis be prevented?
Complete prevention is not possible, but you can greatly reduce the risk by:

• Regular fecal testing
• Consistent record-keeping
• Targeted deworming based on advice
• The right treatment at the right time
• Good pasture hygiene and manure management
• Extra vigilance in young horses
• Avoiding unnecessary deworming that may disrupt larval cycles
  Year-round, well-coordinated worm management is the best protection.