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PA RASITES
- WORMS
Note for Pet Owners
This information is provided
by Provet for educational purposes only.
You should seek the advice of
your veterinarian if your pet is ill as only he or she can correctly
advise on the diagnosis and recommend the treatment that is most
appropriate for your pet.
Note for
Animal Owners:
Your animals may appear to
be normal to you but in fact they may be carrying a large number of
parasitic worms inside their stomach or intestines. Infective stages of
the common parasites survive for a long time in the environment and after treatment
reinfection occurs frequently. In addition, some worms are transmissible
to man (see Zoonosis).
It is therefore important to give routine treatment against the common
worms.
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Description
Worms are classified as helminths and they are parasites
that live inside their host's body. They are therefore known as endoparasites.
Worms can be surprisingly large - the common roundworm of dogs (Toxocara
canis) can grow to 18cm in length !
Cause
There are three main types of helminth of clinical importance:
- Roundworms (nematodes)
- Tapeworms (cestodes)
- Flukes (trematodes)
Worms have a life-cycle which involves stages outside the main host.
Sometimes the life-cycle requires that a parasite stage passes through
another (intermediate) host. Sometimes the infective stage of a worm can
accidentally infect an unusual host - such as happens
Breed Occurrence
Most species of animal can be infected with worms including mammals (dogs, cats,
rabbits, horses, sheep, cattle etc), fish, birds and reptiles.
The distribution of parasites in our domestic animals varies worldwide
depending upon many factors including climate. However the common worms are :
Dogs
Cats
Snakes
- Roundworms
- Lungworms
- Tapeworms
- Flukes
Signs
Animals with parasites may show no signs at all. However, if a host has a
large number of worms it may find it difficult to maintain body condition
and it will lose body weight. In some cases sufficient injury can be caused to
the host to produce signs of disease (eg vomiting, diarrhoea).
Occasionally heavy
worm burdens can cause death.
Life-cycle
Worms sometimes have complex life-cycles which involve a period of
existence and development outside the primary host. In some cases a stage of
development may require passage through an intermediate host
Understanding the life-cycle of a specific parasitic worm is important so
that strategies for treatment and prevention can be designed and implemented.
Diagnosis
Diagnosis is usually made by identifying typical eggs in faecal samples passed
by an animal. Sometimes, as in Toxocara canis or Trichinella
spp dormant larval stages may be recognised in muscle biopsy samples.
In some cases eg the heartworm Dirofilaria immitis larvae can be found in
blood sample.
For some worms (eg D.immitis) there are also serological diagnostic
tests to confirm exposure.
If an animal passes whole worms in faeces they can be identified by
their characteristic anatomical features.
Treatment
Routine treatment of young animals and regular worming of adult animals is
important to reduce the incidence of infection and to reduce environmental
contamination. A wide variety of treatments are available for the
various worm infections that occur in our domestic species. Under certain
circumstances natural resistance can develop so rotation of products is often
recommended - particularly for farm animals.
Prognosis
The prognosis is good for infected animals - except for individuals with a heavy
worm burdens when damage to the intestine wall can lead to ulceration and
even perforation.
Long term problems
Re-infection is a common problem - particularly in animals
that are in contact with a heavily contaminated environment eg pasture,
parkland. Updated October 2013
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