Tapeworm; Understand the facts and manage the risk

Tapeworm

Understand the facts and manage the risks

by Dr Corrine Austin

Internal parasites present a constant challenge for horses, requiring ongoing monitoring and careful management to maintain optimum horse health. Incorrect management can lead to unchecked worm burdens, development of resistance to wormers and in the worst cases, ill health and death.

What is resistance?

Worms can develop the ability to survive the killing effect of wormers, usually through repeated exposure to worming drugs. The risk of resistance emerging is increased by practices such as routine worming strategies or under-dosing with wormers. It is therefore becoming increasingly important to 

The tapeworm Anoplocephala perfoliata
is the most common in the UK.

avoid routinely worming horses and to reserve the use of drugs for when they are really needed – when a horse has a confirmed burden.

The horse tapeworm

Diagram 1 - shows the ileocaecal junction

The most common worms to infect horses in the UK are small redworm (cyathostomins), roundworm (ascarids) and tapeworm (cestodes). Three species of tapeworm are capable of infecting horses; the most common in the UK is Anoplocephala perfoliata. It can grow up to 8 cm long and is made up of a series of segments. The head has four suckers which the tapeworm uses to attach itself to the caecum and to a small region of the intestines called the ileocaecal junction (see diagram 1).  

This localised attachment causes damage to the intestines and the presence of large numbers of tapeworms cause intestinal obstruction and clinical disease, resulting in colic.

Large number of tapeworms cause
intestinal obstruction, resulting
in colic

Diagnosing worm burdens in horses

The most common worms to infect horses in the UK are cyathostomins (small redworm), ascarids (roundworm) and cestodes (tapeworm). Worm egg counts (WEC), should be carried out regularly to monitor for small redworm and roundworm (note: a routine winter worming dose should still be carried out for encysted redworm until a diagnostic test is available). WEC are unreliable for detecting tapeworm burdens as eggs are not uniformly spread throughout the dung. Tapeworm burdens are more accurately diagnosed by either a blood or a saliva test, both of which detect tapeworm-specific antibodies. In the past, the accepted method to control tapeworms was to treat all horses every six months, regardless of whether they needed treating, but since the availability of accurate tests, this practice is no longer necessary or recommended.

The EquiSal Tapeworm saliva test

The EquiSal saliva test is carried out using the specially designed swab provided in the kit to collect saliva. The sample is sent back to the laboratory for testing in a tube containing preservative solution. It is easy to integrate EquiSal Tapeworm testing into your worm control programme – simply test every six months at a time when you would consider routine worming for tapeworm.

The test provides a low, borderline or moderate/high diagnosis and worming is recommended for horses diagnosed as borderline or moderate/high. Diagnostic accuracy has been proven through full validation of the test which has been published in the peer reviewed journal, Veterinary Clinical Pathology.

The EquiSal saliva  swab turns pink after collecting saliva
from a horse to be tested

The importance of routine testing

Routinely monitoring your horse for tapeworm burdens is important as, with other worm species, infection is dynamic and can be influenced by factors outside of your control. This was highlighted recently by results obtained in one of EquiSal’s research studies.

Ama and Charlie graze separately, in a regularly muck cleared field, surrounded by gardens and agricultural land with a bridleway running down one side. Both horses had been diagnosed with low burdens for two years, so it was quite a surprise when Ama’s test results diagnosed her with a moderate/high burden. However, the adjacent bridleway was found to have horse dung left by passing horses and this was enough to infect Ama, who grazes closest to the bridleway. This can be explained when considering the tapeworm life cycle, in which oribatid mites are intermediate hosts (see life cycle section). Oribatid mites living on the pasture would have ingested tapeworm eggs from the dung on the bridleway before moving to the paddock and been inadvertently eaten by Ama.  Ama’s results subsequently reduced to low burden diagnosis after worming.

Tapeworm life cycle

The tapeworm life cycle is different from other horse worms as it requires an intermediate host. Infected horses pass tapeworm eggs onto the pasture where they are consumed by free-living oribatid mites. The eggs develop into larvae within the mite until the mite is ingested by a grazing horse, allowing the larvae to be released into the intestines. The larvae complete their life cycle by attaching to the lining of the caecum or ileocaecal junction, where they develop into adult tapeworms capable of releasing eggs.

Oribatid mites live within the grass and soil of our pastures, but the number of infected mites depends on the level of infected horses grazing the paddocks. If there are a lot of infected horses in a paddock, then a higher proportion of the oribatid mites are likely to be infected. It is essential to manage tapeworm burdens in horses and this also minimises the number of infected mites present.

Testing before treating significantly reduces wormer doses

Routinely testing for tapeworm every six months and only treating horses diagnosed with a burden significantly reduces the doses of wormer being administered to horses, as approximately 75% of horses in the UK are diagnosed with a low burden so do not require treatment.

Case study: testing small herds

Endurance rider Karen Corr’s four horses were tested for tapeworm using the EquiSal Tapeworm kit. One horse, Zee, was found to have a moderate/high tapeworm burden and treated, whilst the three other horses were low and did not need treatment. Six months later, all of Karen’s horses, including Zee, were diagnosed with a low tapeworm burden, so no treatment was needed. Karen’s experiences with EquiSal Tapeworm tells us that targeted tapeworm control has been effective on her yard. Using this approach, only one dose of tapeworm wormer has been necessary for one horse this year, and Karen has been able to only use wormers when they are needed. Avoiding ‘blanket’ use of wormers is an important factor in reducing the risk of resistance emerging. “I’m convinced EquiSal testing should be an important part of our worm control regime,” says Karen.

Case study: testing large herds

In 2016, Bransby Horses, which uses saliva testing for horses in its care as part of its worm control strategy, tested in Spring and Autumn as well as testing horses new to the premises. Only 22% of the 749 test results were borderline or moderate/high and required treatment. This resulted in a big reduction in wormer administered to the horses – 583 doses to be exact!

Certain horses are less prone to tapeworm burdens and graze alongside those with burdens without easily becoming infected. This is similar for other worm species where 80% of all worms are said to be present in 20% of horses. It is also interesting to note that horses with tapeworm burdens aren’t necessarily the same horses with a tendency to have high WEC results.

Reducing the risk of tapeworm infections

Although it can be difficult to influence management practices outside of your own field to prevent infection, it is best practice for horses in adjacent paddocks to be following the same worm control programme.

It is important to carry out routine paddock management, such as regular muck clearance, where muck is completely removed from grazing and adjacent areas, as well as field rotation and resting where possible. It is also important to restrict horses’ grazing while away from home, such as at show grounds. Lastly, ensure you know your horse’s accurate weight for correctly dosing wormers as under dosing can result in persistent burdens and continuous egg shedding.

This article first appeared in the March 2017 issue of equine magazine. An annual subscription to equine costs just £20 for 11 issues - visit the TheEquineStore.co.uk to take out a subscription now.