The dangers of tapeworm and encysted small redworm


Tapeworms are the largest worms to affect horses in the UK. While the most common type can grow up to 20cm long, there is a less common type which can grow to a whopping 80cm in length!

Tapeworms are white, flattened, segmented worms. The adult worms attach themselves at the junction of the small and large intestine. They draw nutrients away from the horse and in large numbers can cause loss of condition and an obstruction which can lead to colic.

Tapeworms won’t reliably show up in a standard faecal worm egg count.  This is because the tapeworm eggs are contained within the body segments of the tapeworm, which intermittently break off to be passed out in droppings.  It is sometimes possible to pick up some tapeworm eggs on a faecal egg count but because of the intermittent shedding and containment in body segments, absence of eggs seen does not rule out tapeworm infection.  Therefore, even if your horse has a negative faecal worm egg count it could still have a tapeworm burden.

You can carry out a saliva test to see if your horse needs to be treated for tapeworm.

Encysted small redworm (encysted cyathostomes)

In the spring, summer & early autumn months, regular faecal worm egg counts (FWECs) can identify eggs produced by adult small redworm and other types of worm. These FWECs are an important part of a targeted worming programme. However, FWECs will not pick up small redworm in their encysted stages, which is why they can be misleading in the winter.

During the colder months, small redworm ingested by your horse can ‘hibernate’ within cysts in your horse’s gut wall. These encysted small redworm don’t lay eggs, which is why a FWEC cannot identify their presence. When the weather warms up, these encysted small redworm start to emerge as adults and this mass emergence may cause very severe damage to your horse’s gut resulting in diarrhoea, colic and sadly, death.

A blood test is now available to detect small redworm antibodies and with time, it is hoped that a saliva test will also be developed to make the option of identification more cost effective. Horses over 6 months of age should be blood tested or treated for encysted stages of small redworm using an appropriate wormer to prevent the dangerous build-up of larvae. You should give the wormer to your horse at the end of the grazing season when the weather gets colder to reduce your horse’s chances of picking up worm larvae from the pasture, and therefore causing ongoing pasture contamination.

Looking after your horse’s environment will also help to reduce the spread of redworm and other parasites.