THE PET HEALTH LIBRARY
Roundworms: Dogs & Puppies
By Wendy C. Brooks, DVM, DipABVP
Educational Director, VeterinaryPartner.com
There are two species
of roundworms affecting dogs and puppies: Toxocara canis and Toxascaris
leonina. Both are treated with the same medication protocol so when
eggs are seen on a fecal flotation
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adult Toxacara worms
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exam, it is not necessary
to determine which species is present.
HOW INFECTION OCCURS:
In dogs, there are four ways by which infection with Toxocara canis
occurs:
Consuming infective worm eggs from soil in the environment (generally
through normal grooming).
Nursing from an infected mother dog.
Consuming a prey animal (usually rodent) that is carrying developing
worms.
During embryonic development when an infected mother dog is pregnant
(most puppies are infected this way).
Note: cats cannot be infected with Toxocara canis.
LIFE AS A ROUNDWORM:
Toxocara canis has one of the most amazing life cycle in the animal
kingdom. It is crucial to understand this life cycle if effective treatment
is to be pursued.
STEP ONE: Toxocara eggs are passed in the host's feces. If
a fecal sample is tested, the eggs can be detected. The embryonic worm
develops in the outdoor environment inside its microscopic egg for one
month before it becomes able to infect a new host. If environmental conditions
are favorable, it takes about a month for the egg to become infective
but Toxocara eggs are famous for weathering harsh environmental conditions.
Eggs can remain infective for months to years. Note: Fresh feces are
not infectious.
STEP TWO: The egg containing what is called a second stage
larva is picked up by a dog or by some other animal. The egg hatches
in the new host's intestinal tract and the young worm burrows its way
out of the intestinal tract to encyst in the host's other body tissues.
If the new host is a dog, the life cycle proceeds. If the new host is
a member of another species, the larvae wait encysted until the new host
is eaten by a dog.
STEP THREE: These second stage larvae can remain encysted
happily for years. If the host is a dog, the larvae mostly encyst in the
host's liver. When the time comes to move on, the larvae excyst and migrate
to the host's lungs where they develop into third stage larvae. They burrow
into the small airways and travel upward towards the host's throat. A heavy
infection can produce a serious pneumonia. When they get to the upper airways,
their presence generates coughing. The worms are coughed up into the host's
throat where they are swallowed thus entering the intestinal tract for
the second time in their development.
If the host is pregnant, the larvae do not migrate to the lung after
they excyst; instead they home to the uterus and infect the unborn puppies.
The second stage larvae make their way to the puppies lungs to develop
into third stage larvae.
If the host is a nursing mother, second stage larvae can migrate
to the mammary gland instead of the lung after excysting. Puppies can be
infected by drinking their mother's milk, though, due to the intrauterine
cycle described above, the litter would probably already be infected.
Note: When dogs are dewormed, this affects only worms in
the intestinal tract. It does not affect encysted larvae. It is very
difficult to prevent mother to puppy transmission and routine deworming
is not adequate.
STEP FOUR: Once back in the intestine, the larvae complete
their maturation and begin to mate. The first eggs are laid about one
week after the fourth stage larvae have arrived in the intestine and about
4 to 5 weeks after infection has first occurred. From here the cycle repeats.
WHY IS INFECTION BAD?
Roundworm infection can have numerous negative effects. It is a
common cause of diarrhea in young animals and can cause vomiting as well.
Sometimes the worms themselves are vomited up which can be alarming as
they can be quite large which females reaching lengths of up to seven
inches. The worms consume the host's food and can lead to unthriftiness
and a classical pot-bellied appearance. Very heavy infections can lead
to pneumonia as the worms migrate and, if there are enough worms, the
intestine can actually become obstructed.
It should also be noted that human infection by this parasite is
especially serious (see below). It is important to minimize the contamination
of environmental soil with the feces of infected animals so as to reduce
the exposure hazard to both humans and other animals.
HOW DO WE KNOW IF OUR DOG IS INFECTED?
You may not know and this is one of the arguments in favor of regular
deworming. Regular deworming is especially recommended for dogs that
hunt and might consume the flesh of hosts carrying worm larvae. Puppies
are frequently simply assumed to be infected and automatically dewormed.
Of course, there are ways to find out if your dog is infected. If
a dog or puppy vomits up a worm, there is a
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Toxocara Egg
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good chance this is a
roundworm (especially in a puppy). Roundworms are long, white and described
as looking like spaghetti. Tapeworms can also be vomited up but these
are flat and obviously segmented. If you are not sure what type of worm
you are seeing, bring it to your veterinarian's office for identification.
Fecal testing for worm eggs is a must for puppies and a good idea
for adult dogs having their annual check up. Obviously, if there are
worms present, they must be laying eggs in order to be detected but, by
and large, fecal testing is a reliable method of detection.
HOW DO WE GET RID OF ROUNDWORMS?
Numerous deworming products are effective. Some are over the counter
and some are prescription. Many flea control and/or heartworm prevention
products provide a monthly deworming which is especially helpful in minimizing
environmental contamination. Common active ingredients include:
Febantel (active ingredient in Drontal and Drontal plus)
Pyrantel pamoate (active ingredient in Strongid, Nemex, HeartgardPlus
and others)
Piperazine (active ingredient in many over the counter products)
Fenbendazole (active ingredient in Panacur)
Milbemycin Oxime (active ingredient of Interceptor and Sentinel)
There are two important concepts to keep in mind about deworming.
Medications essentially anesthetize the worm so that it lets go of its
grip on the host intestine and passes with the stool. Once it has been
passed, it cannot survive in the environment and dies.
This means that you will likely see the worms when they pass, so
be prepared as they can be quite long and may still be alive and moving
when you see them.
The other concept stems from the fact that larvae in migration cannot
be killed by any of these products. After the worms are cleared from
the intestine, they will be replaced by new worms completing their migration.
This means that a second, and sometimes even a third deworming is needed
to keep the intestine clear. The follow-up deworming is generally given
several weeks following the first deworming to allow for migrating worms
to arrive in the intestine where they are vulnerable. Do not forget your
follow-up deworming.
WHAT ABOUT TOXASCARIS LEONINA?
The life cycle of Toxascaris leonina is not nearly as complicated.
They do not migrate through the body in the way that Toxocara does. Instead,
the Toxascaris second stage larva is consumed and simply matures in the
intestine, a process which takes 2 to 3 months. Like Toxocara, Toxascaris
can infect hosts of other species, though with Toxascaris the larvae can
develop into third stage larvae in these other hosts while with Toxocara
larval development is arrested in species other than the dog.
Note: Toxascaris leonina can infect both dogs and cats alike.
Copyright
2001 - 2007 by the Veterinary Information Network, Inc. All rights reserved.
This
work was originally published by Veterinary Information Network, Inc.
(VIN)
and is republished with VIN's permission.
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What are canine roundworms?
Roundworms are parasites which live in the gut of dogs and cats and
can cause illness. They can cause diarrhea, a scruffy coat, pot-bellied
appearance, a cough or block the intestines. There are three roundworm species
affecting dogs and cats, Toxocara canis, Toxocara cati and Toxascaris leonina.
T. canis is the most important type for dogs, and it can be fatal to
puppies. T.cati occurs mainly in cats and is very rare in dogs. T. leonina
occurs in both pets but is much less dangerous. The larvae of these worms
may also cause disease in humans, particularly T. canis.
Adult roundworms, which look like short, fat strands of spaghetti,
reside in the small intestine and can grow to about six inches long. They
feed on bodily tissues and fluids, not blood.
The worms have interesting life cycles. Adults mate in the pet's small
intestine, then the female lays eggs which are passed out of the body
with the pet's feces. The eggs can remain infectious in the environment
for years, as their thick shell makes them relatively resistant to
drying out and much harder to kill.
“[Roundworm] eggs can remain infectious in the
environment for years, as their thick shell makes them relatively
resistant to drying out and much harder to kill.”
Within the egg, the baby worm or larva develops to such a stage that
it is ready to infect a new host. This takes two to four weeks. At this
point, the larvae hopes to be ingested by a passing dog or cat so it can
continue its life cycle.
What happens when a roundworm is ingested depends on the age of the
carrier. In puppies and kittens up to
three months old, the worm migrates through the body to the liver,
then the lungs,where it is coughed up and often swallowed again, so it can
make its way back to the gut. This isn't always successful and some owners
notice their pet coughing up worms. Once the worm is back in the gut, the
life cycle continues.
The bodies of older animals, with more-developed immune systems, react
by trying to contain the parasites, which are normally walled off by the
gut to prevent them migrating any further. They often become trapped in
the wall of the intestines or in the abdominal wall. However, this does
not kill the worms, and they can remain alive in this encysted state for
a year or more.
In adult female dogs which become pregnant, roundworm larvae that have
been dormant are reactivated, probably by hormonal activity. Once again
the roundworms migrate through the body,but in this case, they take a few
different routes:
* to the gut to cause a transient patent infection in
the pregnant female, so that she excretes eggs in her feces.
* via the placenta to the liver of the fetus to infect
it before birth. This occurs only in dogs with T. canis
infections.
* to the mammary glands of the mother, where they are
passed out via the milk so newborn puppies and
kittens become infected when they nurse.
Puppies appear to be the most common victims of roundworm infection.
It has been estimated that over 95 per cent of new puppies are infected
with roundworm! They are also a problem in kittens, which commonly acquire
infection through their mothers' milk. Roundworms may also infect humans.
Kittens and puppies with roundworm usually look pot-bellied. Roundworms
can also cause diarrhea, dehydration, vomiting and leave pets weak and malnourished.
The young pets often have dull, scruffy coats.
“In the very worst cases, the largest worms can
completely block the gut. This can be very painful and can potentially cause
death in affected animals.”
In more severe cases, roundworms can cause pneumonia, as they migrate
through the lungs and can cause coughing, breathing difficulties, a nasal
discharge and weakness or even lead to collapse. In the very worst cases,
the largest worms can completely block the gut. This can be very painful
and can potentially cause death in affected animals.
The popularity of dogs and cats has been highlighted as the major risk
factor for human infection. If accidentally ingested, the immature worms
can migrate to human organs such as the liver, lungs or eyes. The human
body, as with adult dogs and cats, tries to wall them off to prevent them
moving further. The immune reaction can cause a large lump in the body,
occasionally confused with cancer. In humans the disease is known as visceral
larva migrans, or, if in the eye, ocular larva migrans. Children are at
a higher risk of infection due to play habits such as eating dirt, their
attraction to pets and their dislike of hand washing.
“Children are at a higher risk of infection due
to play habits such as eating dirt, their attraction to pets and their dislike
of hand washing.”
There are several ingredients on the market which are effective in
killing roundworms, such as pyrantel, milbemycin and levamisole. Many
of these will also treat other kinds of worms. Your veterinarian can advise
you on the most appropriate choice for your pet.
Current intestinal worm treatment recommendations for puppies state
that they should be treated at two, four, six, eight, ten, and 12 weeks
of age, then monthly until they are three months old, then at least every
three months from then on. Pregnant bitches should be treated from at least
day 42 of pregnancy and fortnightly while the pups are suckling.
Current intestinal worm treatment recommendations for kittens state
that they should be treated at six, eight, ten and 12 weeks of age, then
monthly until they are three months old, then at least every three months
from then on. Pregnant cats should be treated at least ten days before kittening,
and then fortnightly during the time that the kittens are suckling.
References
Kassai T, (1998). Veterinary Helminthology. Butterworth Heinemann,
UK.
Payne P.A., Carter G.R. Internal Parasites of Dogs and Cats. In: A
Concise Guide to Infectious and Parasitic Disease of Dogs and Cats. International
Veterinary Information Service, Ithaca, NY. www.ivis.org
Tilley, L.P., Smith, F.W.K. The Five Minute Veterinary Consult Canine
and Feline. Second Edition. Lippincott Williams & Wilkins, Baltimore,
2000.
A roundworm.
Image:www.cdc.gov
