Pinworms (Oxyurids)
Pinworms are small, white, thread-like parasitic worms that infect the intestines of many animals, including horses, livestock, poultry, and rabbits. Unlike many other internal parasites, pinworms are usually more irritating than dangerous – but they can still cause significant discomfort, stress, and secondary health problems if left unmanaged.
Pinworms are best known for causing intense itching around the anus or tail area, which leads to rubbing, hair loss, and skin damage. While they rarely cause severe disease, they can seriously affect an animal’s comfort, behaviour, and condition.
Why Pinworms Matter
Pinworms live mainly in the large intestine. Adult females migrate out of the anus to lay their eggs on the surrounding skin. This triggers intense itching and irritation.
This can lead to:
Tail rubbing or biting at the hindquarters
Hair loss around the tail and rump
Thickened, irritated, or broken skin
Restlessness and discomfort
Reduced appetite
Weight loss (in chronic cases)
Reduced productivity
Although pinworms rarely cause life-threatening illness, they can significantly affect welfare and are often a sign of hygiene or management issues.
Pinworms in Different Animals
Equines (Horses & Donkeys)
Pinworms are a common cause of tail rubbing in horses. Affected animals may scratch their hindquarters against fences, walls, or posts.
Typical signs include:
Broken or missing tail hairs
Raw or thickened skin under the tail
Irritability
Restlessness
Because pinworm eggs are laid on the skin rather than passed consistently in manure, they can be difficult to detect with standard faecal tests.
Rabbits
Pinworms are very common in rabbits, especially in group housing or breeding environments. The most common species is Passalurus ambiguus.
Many rabbits show no obvious signs, but heavier burdens can cause:
Itching around the tail
Dirty or matted fur around the hindquarters
Soft stools
Weight loss
Reduced appetite
Poor coat condition
Young rabbits are particularly susceptible, and reinfection is common if hygiene is poor.
How Pinworms Spread
Pinworms have a direct life cycle.
Female worms lay eggs on the skin around the anus. These eggs become infective quickly and can spread through:
Contaminated bedding
Feed and water
Grooming
Shared surfaces
Litter trays or hutches
Animals can reinfect themselves or spread the eggs to others very easily.
Because pinworm eggs are sticky and resistant, they can persist in the environment for long periods.
Signs of a Pinworm Burden
Pinworm infections often show up as behavioural and skin-related signs rather than digestive illness.
Common indicators include:
Tail rubbing or scratching
Hair loss around the tail or rump
Irritated or broken skin
Restlessness
Reduced appetite
Weight loss (in chronic cases)
Poor coat condition
In rabbits, signs may be subtle and easily missed.
Detection
Pinworms are not always easy to detect with standard faecal egg counts.
Detection may involve:
Adhesive tape tests (for eggs around the anus)
Visual inspection of the tail and hindquarters
Reviewing clinical signs and behaviour
Because pinworm eggs are laid on the skin rather than consistently passed in manure, clinical signs are often just as important as laboratory testing.
Treatment & Long-Term Control
Pinworms are usually easy to treat, but reinfection is common if the environment is not properly managed.
Long-term control involves:
Targeted treatment based on detection
Thorough cleaning of bedding, stables, hutches, and enclosures
Washing tail and hindquarters to remove eggs
Good hygiene of feeding areas
Avoiding overcrowding
Regular monitoring
Without proper environmental control, animals may appear to be “constantly reinfected,” even after successful treatment.