Page 71 - The Veterinary Care of the Horse

state in the droppings of an infected horse. Diagnosis is made by identification of the worms

or by viewing eggs under the microscope that have been collected from the skin around the
VetBooks.ir anus using cellophane tape.

Treatment and control Resistance of pinworm infestations to anthelmintic treatment are
increasingly being reported, so ask your vet for advice as a course of treatment may be

necessary, rather than a single dose. Following anthelmintic treatment the perineal region and
tail head should be bathed with a mild, non-irritant cleansing agent and gently dried using
disposable materials. This should be repeated once or twice every day. The worms tend to lay

their eggs at night when the horse is resting so morning cleaning is important. The success of
treatment is monitored by cellophane tape tests repeated at weekly intervals for up to a month

after treatment. Grooming kits, feed and water buckets should be thoroughly cleaned,
together with any surfaces the horse may have rubbed against. Contaminated bedding should

be disposed of.

THREADWORM – Strongyloides westeri

This is a very small worm that can cause diarrhoea in young foals aged between 2 weeks and

4 months.
Colour and size 2–9 mm ( in), translucent, white.

Life cycle Infective larvae pass to the foal in the mare’s milk. They are swallowed and on

reaching the small intestine, they develop into egg-laying adults within 8–15 days. The eggs
pass out in the faeces and can develop into infective larvae within 24 hours in warm, damp
conditions. The larvae are also capable of completing their life cycle in the environment, thus

increasing the numbers that can infect the foal. The foal may eat the larvae or they can
penetrate the skin and migrate through the liver and lungs. They are then coughed up and

swallowed. Once in the small intestine, the larvae develop into adults.

In adult horses, the larvae penetrate the tissues and do not continue their development to
adults. When the mare starts to produce milk after foaling, the larvae migrate to the udder
and infect the foal.

Clinical signs Heavy infections result in yellowish diarrhoea which may contain blood.

Severely affected foals lose weight and can become dehydrated. Large numbers of larvae
migrating through the lungs occasionally cause respiratory signs.

Diagnosis This is made on the clinical signs and the presence of large numbers of eggs in the
faeces.

Treatment For advice on treating such young foals, consult your vet.

Control Treating the mares with ivermectin just before they foal will reduce the numbers of