This is now the most common worm found in horses today - the majority of eggs in faeces or larvae on the pasture being those of the small redworm (Mair T et al, 1990). The life cycle of the small redworm, as shown, is from 6 weeks, but can last as long as 2 years (Love S et al, 1999).

Size/Appearance: The small redworm is up to 2.5cm long, thin and reddish in colour.

Location in Horse: The L3 infective larvae are ingested by the horse from the pasture; they then migrate to the large intestine where they burrow into the gut wall and become encysted. They may develop quickly into L4 larvae and emerge into the gut to become adults. However, up to 85% of the encysted larvae may become dormant, known as inhibited encysted larvae (EL3). Tens of thousands of these encysted larvae can line the gut wall, where they impair absorption of nutrients, possibly resulting in weight loss and life-threatening illness (Love S et al, 1999). These inhibited encysted larvae can emerge ‘en-masse’ without warning. Potentially fatal, this emergence typically occurs during the late winter / early spring and is known as Larval Cyathostominosis. Severe cases can result in a 50-60% chance of death. Young horses (less than 6 years of age) can often be at higher risk of the disease (Abbott E, 1998), but small redworm can cause life-threatening illness at any time of year and in any age of horse.

Symptoms: Symptoms range from diarrhoea to rapid and severe weight loss, colic and even death.