Once thought relatively benign, the tapeworm is now known to be a potential danger.
Unlike other worms in the horse, tapeworms develop inside an intermediate host — the microscopic forage mite.
Horses become infected when they eat hay or grass containing mites, which are themselves infected with tapeworm larvae.
These then develop into adult tapeworms inside the horse’s intestines.
Testing for tapeworms
Testing for tapeworms can be tricky. Horses can have large tapeworm burdens and appear healthy on the outside.
Counting the tapeworm eggs in a faecal worm egg count (FWEC) is unreliable. Egg numbers are usually low and encased in the segmented tapeworm parts rather than distributed evenly throughout the droppings.
A negative result on a FWEC does not therefore mean your horse is free of tapeworm.
Instead of a FWEC, we can use a blood sample to test for infection, a method known as the ELISA or tapeworm antibody test. A horse with a high level of tapeworm infection will produce a large number of antibodies, which can be detected in the blood.
The test indicates a broad level of intensity, rather than tapeworm numbers. The amount of antibodies will indicate whether the burden is low, medium or high.
While the blood test is useful for assessing whether your horse has been infected with tapeworms in the past, it is not a reliable indicator of response to treatment.
This is because it takes around four to five months for the antibody levels to return to normal after the worms have been killed. Therefore the test only needs to be carried out once a year.
Horses with evidence of a high tapeworm burden on a blood sample are likely to be susceptible to infection with tapeworms in the future. They should be treated a second time that year, before being retested 12 months later.
There are two different approaches to tackling tapeworm. Treatment can be targeted, following a blood test, or administered within an annual worming programme.
With targeted treatment, your vet will combine information on the horse’s worming history with FWEC and blood test results to decide whether he needs worming — and the most appropriate treatment if this is necessary.
Targeted treatment can reduce the likelihood of worms becoming resistant to treatment and identifies horses at risk of high levels of worm infection.
Using this method, horses are blood-tested for tapeworms once a year. Those with a high burden are treated after the test and then again six months later. The blood sample is then repeated the following year.
New horses on the yard should have a blood test and a FWEC, or be treated for both tapeworms and roundworms, before they are turned out with others.
In some yards, targeted worming may not be suitable nor practical. In these instances, it is best to treat for tapeworms every six months.
Tapeworm infection is not strongly linked to seasonality, so the time of year that treatment takes place is not particularly important. As risk is higher after prolonged periods of grazing, however, it seems wise to treat at the end of a summer out at grass.
It is important to be aware that not all wormers kill tapeworms. The parasites can be treated with one of two drugs — praziquantel and pyrantel. The latter must be used at a double dose.
Fortunately, both drugs are very effective and cause death and detachment of the tapeworms from the gut wall within 24-48hr following treatment. They are available as single products or in combination with other drugs that target different types of worms.
Parasite populations on the pasture can be reduced by regular removal of droppings, resting grazing and rotating sheep and cattle on to horse fields.
To conclude then, careful pasture management combined with correct testing and treatment will ensure that tapeworm infection is controlled.
The full veterinary article about tapeworms was first published in Horse & Hound magazine (7 March 2013)
Read more about worming