NEMATODES
LARGE REDWORMS (Strongylus vulgaris)
Adult Large redworms worms vary in size between 1.5 and 5 cm. Large redworm was once the most
important parasite affecting the horse because the migrating larval
stage damage the lining of the arteries, particularly those supplying
the gut. However in the UK older horses have usually developed
immunity due to the efficient use of equine wormers in this country.
Large redworm infection is more generally a problem in younger horses.
These worms migrate through and damage some of the the body's vital
organs.
LARGE ROUNDWORMS / ASCARIDS (Parascaris equorum)
Large roundworm also known as ascarids are very long worms up to 40cms when mature and produce large numbers of tough coated adhesive
eggs which stick any surrounding environment. They
are white in colour. They can stick to
the coat and udders of the mare and even to the walls and stable floors.
The eggs have very thick shells and therefore can survive on pastures
over the winter months. These worms are eventually coughed up by the
horse and then renter the body to be re-circulated once more.
This complex lifecycle creates great potential for disease.
Respiratory obstruction is common as a result of the presence of the
larval stages in the lungs. Intestinal blockage and impaction colic
is also common in foals due to the sheer size of the adult
parasites. Their presence in the intestine can block the passage of
part-digested food material. In addition, there is loss of vitamin A
from intestinal chyme, which can retard growth and development.
HAIRWORMS (Trichostrongylus axei)
Adult hairworms are only about 7cms in length and so are very hard to
see with the naked eye. These worms are usually controlled by
products containing Moxidectin or Ivermectin. They are unusual as they are also a parasite of sheep
cattle and pigs. As the name suggests they live in the stomach where
they feed on blood. The larvae then migrate via the bloodstream to
various body tissues and mature on the intestine. Threadworm larvae
can penetrate the mammary tissue and be transmitted to young suckling
foals via the mothers milk.
STOMACH HAIRWORMS (Habronema
muscae)
Stomach hairworms are 1-2.5cms in length and are long slender
and white in colour.
These worms are usually controlled by the worming programmes
containing Moxidectin or Ivermectin but are unusual as they are also a parasite of sheep
cattle and pigs. They develop into adults in the stomach where they
feed on blood. These worms are transmitted by flies landing on
and ingested dung so fly control measures will help to reduce
infections. They are also capable of remaining on and damaging the
skin and causing "summer soreness".
PINWORMS
(Oxyuris equi)
Pinworm burden is becoming an
increasing problem for UK horse owners. Pinworm (Oxyuris equi) is
not generally
considered harmful but more of a nuisance
and an irritant. The female can grow up to approximately 10cm in
length and are white in colour. They reside in the large intestine
and attach them selves to the intestinal wall to ingest the contents
for food.
Adults produce eggs approximately 5 months after the initial
infection which are found on the pasture, in faeces, contaminated
water fences and walls.
Eggs are ingested by the horse and L3 larvae are released in the
small intestine, they then migrate to the large intestine to develop
into the mucosa to L4 larvae which then emerge and mature into
adults. The female adults then migrate from the large intestine to
the anus where they lay eggs in clumps on the perineal skin causing
irritation around the anus leading to tail rubbing.
Active ingredients that treat for adult
and pinworm larvae are Moxidectin, Ivermectin, Febendazole and
Mebendazole with Pyrantel treating adults only. Not all brands are
licensed so care needs to be taken by checking the brand’s label.
Extra care should be taken in
the stable environment to help reduce the risk of re-contamination
from buckets, feed bowls, haynets and rugs etc. Do not share
grooming brushes. A thorough clean with a heavy duty disinfectant
in these areas and most importantly the stable after removing all
bedding will help and is always a good idea in areas of animal care
and management.
In some
circumstances it may be possible for your vet to prescribe special
preparations or treatments.
LUNGWORMS (Dictyocaulus arnfieldi)
Lungworms are white in
colour and are between 6 and 10 cm in length. The lifecycle of
lungworms is different to other nematodes as adults settle in the
lungs rather than the intestine. Eggs are laid then travel up the
trachea, are swallowed and passed out in the faeces. Further
development then takes place on the pasture, infective larvae are
swallowed by horses or donkeys to further develop into egg laying
adults.
It is extremely rare for lungworm larvae to develop to full maturity
in horses as the horse is not a good host for that particular
parasite. Horses can be infected with lungworm but as they do
not mature in to egg laying larvae in any numbers to sustain a
population on the pastures. Exceptions to this in horses can
arise in very young or old horses and seriously depilated horses
whose immune systems are
impaired.
It has been remarked that a large percentage of donkeys carry
lungworms (more recent research is now disputing this with levels
been quoted as low as 4%) often showing no clinical signs of
infestation and it is in donkeys where the parasite reaches full
maturity. Donkeys do not always develop the symptomatic cough that
is seen in horses but if horses are grazed along side donkeys then
particular care must be taken to treat for lungworms accordingly
with particular attention to foals as they can sustain permanent
lung damage if infected
