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
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