Worms in Dogs
As the name
would suggest, internal parasites live inside their host. There are several
types of internal parasites which can infect the dog, this article will
address some of the more common ones.
There are
several types of works which infect dogs, some of which include;
Heartworm:
Caused by
Dirofilara immitis, heartworms are a potentially fatal parasitic worm living
in the pulmonary arteries, lungs & hearts of dogs. Heartworms are nematodes,
a type of roundworm, they are several inches long, thin & white.
In an
infected animal, the adult heartworms produce their young, known as
microfilaria, which swim around the bloodstream. Microfilaria require an
intermediate host in the form of the mosquito. The mosquito bites an
infected dog & takes up some of these microfilaria circulating in the dogs
blood. Once inside the mosquito, they undergo further maturation, which
takes 10 - 14 days, in which time they become infective larvae. When the
mosquito feeds from a dog or dog, these infective larvae are injected into
the animal.
Symptoms of
heartworms are often non-specific in dogs. Some symptoms include:
-
Coughing
-
Wheezing
-
Difficulty breathing
-
Anorexia
-
Vomiting
-
Lethargy
-
Weight loss
-
Some dogs show no signs at all, but die suddenly
Diagnosis of heartworms in dogs is often difficult and not always 100%
reliable. There are several tests which your veterinarian may perform,
including;
Antibody test: Detects antibodies made by the dog,
to adult heartworm antigen. This may give false positive results if the dog
has had a prior heartworm infection which has cleared up. Also, it is
possible for the dog to have had microfilaria in the blood & removed this
without them developing into adult worms.
Antigen test: Detects the presence of heartworm
antigen in the blood. This relies on the dog being infected with an adult
female heartworm, so may give false negatives if the dog is infected with
male only or immature heartworms.
Echocardiogram (ultrasound reading of the heart):
To detect the presence of heartworms.
Radiography: May detect enlarged pulmonary
arteries possibly with ill defined margins & an enlarged right hand side of
the heart & lung changes.
Microfilarial Tests: This tests for the presence
of microfilaria in the blood. Less than 20% of dogs will have microfilaria
in the blood. This may be due to several reasons. As dogs often only have
one or two heartworms, they may male only or female only, which would rule
out mating of worms producing microfilaria. Also, the dog's immune system
may be attacking & destroying any microfilaria present. Therefore a negative
blood test will not rule out the presence of heartworms.
Tapeworm
Tapeworms
are a highly specialised intestinal parasite known as Cestodes. Tapeworms
need two hosts, the intermediate host which passes the cysticercoid around &
the final host (your pet), where it develops into an adult tapeworm & lays
its eggs. Dipylidium canium is the most common tapeworm in dogs followed by
Taenia taeniaeformis. Tapeworms are hermaphroditic, which means they contain
both ovaries & testes & are capable of reproducing on their own.
Dipylidium
canium: The most common tapeworm found in dogs. The dog flea is the
intermediate host of dipylidium canum. Eggs are passed in the faeces & eaten
by flea larvae. Once inside the flea larvae, the egg hatches & becomes (cysticercoid).
The flea larvae develops into an adult flea, which goes about its business
of parasitising your pet & sucking blood. Your dog (or dog) then ingests the
flea during grooming. Once inside the stomach the flea is broken down & the
tapeworm is released. It hooks onto the small intestinal wall & develops
into an adult tapeworm. Once it reaches maturity (in around 2 - 3 weeks) egg
filled segments break off & leave the body via the anus. These segments have
the appearance of rice grains. These segments are motile (capable of
movement). Once these segments have dried out they have the appearance of
sesame seeds. They are then eaten by flea larvae & so the cycle begins once
again.
Taenia
taeniaeformis: Probably the second most common tapeworm in dogs. Dogs become
infected with taenia taeniaeformis via eating rodents containing the larval
tapeworm.
The presence
of rice like segments (proglottids) around your dog's anus & in the
environment is a sign your pet has tapeworm.
Your
veterinarian may perform a microscopic study of the pet's faeces to check
for the presence of tapeworm segments & or eggs.
Roundworm:
There are
two species which affect dogs, Toxocara dogi and Toxascaris leonina.
Toxocara dogi is more commonly found in dogs. They feed upon the intestinal
contents, competing with the host for food. Roundworms are around 3 - 5
inches long & spaghetti like in appearance.
There are
three modes of transmission, all of which occur when the dog consumes the
infective eggs. It is possible for larvae to be encysted in the tissues from
an earlier infection.
-
Transmammary transmission (Toxocara dogi): When a dog is infected
with roundworm, some larvae migrate to other tissues in the body.
Pregnancy re-activates these larvae which migrate to the mammary
glands & are passed onto the kittens via the mother's milk.
-
Hunting: Rodents can act as intermediate hosts to roundworm & when a
dog kills & consumes its prey.
-
Environmental: Dogs ingest roundworm eggs containing infective
larvae from the environment such as soil, or when they come into
contact with the faeces of an infected dog.
Signs of
roundworm infection include:
-
Poor coat condition
-
Diarrhea
-
Vomiting
-
Pot bellied appearance
-
Severe cases can lead to pneumonia & intestinal & bowel blockage
Hookworm:
Hookworms
are a common intestinal parasitic worm found in dogs & dogs. They are less
common in dogs than they are in dogs.
Hookworms
live in the intestine of the host it infects. Hookworms have teeth like
mouth parts which they use to attach themselves to the intestinal wall &
feed off the host's blood.
There are
several ways dogs can become infected with hookworms & it is important to
understand the life cycle of hookworms, which will be explained below.
-
In Utero: In dogs, worm eggs can be passed on from mother to her
unborn kittens via the placenta. It hasn't been established if this
is the case with feline hookworms yet.
-
Via the mother's milk: Again, in dogs it is possible for hookworm
infection to be passed to her puppies via the breastmilk. When a dog
becomes infected with hookworms most of them migrate to the small
intestine. However, some enter other tissues of the body, becoming
dormant for years. When the animal becomes pregnant, they migrate to
the mammary glands & are passed through the milk. It hasn't been
established if this is the case with feline hookworms yet.
-
Via the skin: Hookworm eggs are passed in the dog's stool. Depending
on conditions, within 2 - 5 days these eggs hatch into larvae
(immature worms), which are present in the moist environment of
soil, & vegetation. When a dog comes into contact with an
environment infected with hookworm larvae, it either becomes
infected via ingestion of the larvae, or they enter the body by
burrowing into the skin.
-
Via ingestion: Hookworm larvae can contaminate food & water which
the dog consumes.
Symptoms of hookworms include;
When they
suck blood from their host, they release an anti-coagulant (a substance
which prevents the blood from clotting). This results in black or bloody
stools.
-
Anaemia (weakness, pale gums)
-
Dull coat
-
In kittens, stunted growth
Other worms:
There are
several other worms which infect dogs but little information is available on
them at present. I will endeavour to list these in more detail in the
future. These worms include;
Lungworm,
Thread Worm, Stomach worms, Bladder worms.
Treatment
of parasitic worms in dogs:
There are
many excellent products on the market to treat the more common worms such as
tapeworm, roundworm & hookworm including tablets & topical products which
are applied to the back of the neck. Your veterinarian is the best person to
speak to in regards to which product will suit your dog best.
There are no
approved methods to treat heartworm in dogs. The treatments which are
available are themselves dangerous. A single dead worm can be fatal in dogs
as it can break away & cause a blockage of the pulmonary artery (pulmonary
embolism.
If there are
no clinical symptoms your vet may decide not to treat the dog & wait for it
to clear the parasite in its own time. As stated earlier, heartworms live
for around 2-3 years in dogs. If this is the chosen method, your
veterinarian will want to monitor your dog every 6-12 months for signs of
complidogions.
If the dog
is displaying symptoms of heartworm disease supportive therapy may be
recommended. Prednisone may be given to the dog to reduce the inflammation &
reaction to the worm.
Dogs with
severe symptoms may require additional supportive therapy such as a
bronchodilator to open the airways, oxygen therapy & intravenous fluids.
Adulticide
treatment may be recommended for dogs with clinical signs who are not
responding to supportive care. Caparsolate is the drug used & kills the
adult worms. This carries risks, as a dead worm can result in a pulmonary
embolism. Around 1/3rd of dogs receiving treatment will face life
threatening complidogions as a result of the dying worms. Confinement will
be necessary for a few weeks after treatment. Either way, if you choose to
let nature take its course & hope that the worm lives out its lifespan
within the dog, or if you use an adulticide there are risks. These must be
weighed up by your veterinarian before a decision is made. Surgical removal
of the worms has been used in some cases.
Can I
catch worms from my dog?
Yes you
can. Although humans are more commonly affected by pinworms, which are a
common type of worm found predominently in school aged children.
Read here for more
information on pinworms.
Tapeworm:
Yes & no.
You cannot catch tapeworm directly from your dog, but if your dog has fleas,
it is possible to catch tapeworm by accidentally swallowing a flea carrying
the tapeworm cysticercoid.
Hookworms:
You can,
although they can't develop into the adult form as they do in dogs. The
infective larvae are found in the soil or sandy areas such as beaches or
children's sandpits are able to penetrate the skin & they migrate, causing a
red, itchy skin eruption. This condition is known as 'Cutaneous Larva
Migrans' (also called 'creeping eruption' or 'ground itch'). The hookworm
larvae cannot complete their life cycle & die in the epidermis.
Roundworms:
Toxocariasis
is a disease in humans caused by infection of the roundworm egg. Most cases
have been identified as those of T. canis. Occasionally T. dogi has been
identified. In humans roundworms can't go past "stage 2" (larval stage). As
with infection in rodents, the larvae migrate to various tissues in the body
(causing a disease called visceral larva migrans or toxocariasis) including
the lungs, brain, eyes & liver.
There are
two forms of toxocariasis:
-
Ocular larva migrans (OLM) results from the larvae entering the eye,
causing an inflammatory response, which leads to damage to the eye,
in severe cases it can result in blindness.
-
Visceral larva migrans (VLM): The larvae migrate to the various
organs and cause an (inflammatory immune response) which leads to
damage to the organs.
-
The larvae can remain alive for many months, causing damage by
migrating through tissues.
Please note:
The medical
articles on this site have not been written by a
veterinarian & should not be considered a replacement for a
veterinarian visit. The articles are provided for
informative purposes only.
Always seek
immediate veterinary advice for any problems (health or
behavioral) in your pets.
While great
care has been made in the creation of these articles, we
cannot guarantee the accuracy or omissions on these pages.
If in any doubt whatsoever, seek professional medical
advice. aaa |
