A parasite is a plant or animal that lives upon or within another living organism. There are a variety of parasites that
infect various organs or body systems. Parasites can be either internal or external parasites – living primarily on the
skin (fleas), in the respiratory tract (lungworms), or in the blood vessels and heart (heartworms).
Some gastrointestinal parasites are microscopic, and the only way to diagnose them is by microscopic examination
of your dog’s feces for the eggs shed by the adult worms. Others are large enough to be observed in your dog’s
bowel movements or after he vomits. Moreover, some tapeworms produce epiglottis, which are the segments
making up their body. These segments can be seen around the hair on the anus or in the stool, appearing as bits
of moving “white rice.”
Among the important gastrointestinal parasites of dogs are roundworms (Toxocara species), hookworms
(Ancylostoma caninum, Ancylostoma braziliense and Uncinaria stenocephala), whipworms (Trichuris vulpis,
T. campanula, T. serrata), stomach worms (Physaloptera spp.), tapeworms (Diplylidium caninum, Taenia
pisiformis), and microscopic parasites Coccidia, Giardia and Strongyloides species.
Scroll down to find out all about specific types about worms
How Parasites Are Acquired
Ingestion of eggs. Most infections are acquired by ingestion of microscopic eggs. This occurs when a dog licks
areas where other dogs have defecated, like yards, parks or grass.
At birth. Many puppies are born with intestinal parasites (usually roundworms) that have been passed from the
mother, where the parasite was in an encysted, quiet state.
From intermediate host. Tapeworms are transmitted by an intermediate host when a dog swallows a flea or
eats a rabbit.
It should be emphasized that some parasites – especially roundworms and hookworms – can also affect people,
especially children. For that reason, it is essential to prevent intestinal parasites in our pets and to treat any
resultant infection.
Parasitic diseases range from trivial to fatal disease. Parasites can cause severe disease in immature puppies, sick
or debilitated pets, or in pets with a suppressed immune system. Younger pets often get acute disease (vomiting,
diarrhea, dehydration, and anemia) whereas older pets get chronic disease such as intermittent diarrhea.
What to Watch For:
Nausea
Vomiting
Diarrhea
Anemia
Skin lesions
Diagnosis
Because parasitism is easily confused with other debilitating conditions, diagnosis depends on the following:
Medical history and physical examination, including observations of worms in the stool or vomitus.
Fecal examination for microscopic eggs or larvae. This is the most common approach to diagnosis as most pets
do not appear ill.
CBC – Complete blood count if anemia is suspected (as with a hookworm infection) or if the pet is showing
symptoms of illness.
Other blood tests may reveal concurrent problems.
Treatment
Treatments for intestinal parasites may include one or more of the following:
Routine deworming in puppies – This is the ideal approach. All immature pets should treated at the first veterinary
examination and regularly dewormed during the first year. In general, every dog less than one year of age should
be given an anthelmintic (anti-parasite drug) for ascarids regardless of fecal results. This is in part to protect the
environment from contamination with microscopic eggs that might infect children.
A yearly fecal check and treatment is recommended for adult pets, especially if they are not taking heartworm
preventatives that would prevent development of intestinal worms.
Other treatments may include fluid therapy for debilitated pets or blood transfusion and iron supplementation
(if necessary for severe blood loss as with hookworm infections).
Home Care and Prevention
At home administer any prescribed medications and follow-up with your veterinarian for examinations and repeated
fecal (stool) tests as needed.
Some microscopic eggs can live in the environment (such as the yard) for weeks to months and cause re-infection.
Clean up yard weekly and minimize roaming of pets in places like parks where exposure and infection are possible.
Many health care specialists recommend a fecal sample from all adult animals at least yearly, a sample at each puppy vaccination visit, and a follow up sample at the appropriate interval after the last deworming medication has been given.
With primarily outdoor dogs, it may be advisable to evaluate stool samples every three to six months if risk of infection is high. One may also consider heartworm preventatives that also prevent intestinal parasites.
Roundworms
Roundworms (Toxocara canis and Toxascaris leonina) are found in the intestine of dogs and are a major hygienic
concern because they are transmissible to people. Because people get infected by ingestion of dirt contaminated with the feces of infected dogs, roundworm elimination should be the concern on every responsible pet owner. An average- sized dog passes 136 grams of feces daily and it is known that a dog with a "light" roundworm infection may pass 10,000 eggs in every gram of stool. If 12% of the 80 million dogs in America have "light" infections, 1,300 metric tons of dog feces containing 13 trillion roundworm eggs are discharged in the streets and lands of America every day!! In different surveys, 0.3 - 15% of soil samples and 7 - 31% of house yards or children's sandboxes contained roundworm eggs.
Your plan of attack to eradicate roundworm infection should be: to eliminate roundworm infection from dogs; to
prevent dog defecation in areas frequented by people, and; to educate your family and friends about the risks and
appropriate control measures.
Concerned pet owners should collect their pet's feces every day and place them in the garbage. Flushing the
feces down the toilet is inappropriate because many eggs survive sewage treatment. While the transmission rate
through this avenue of infection is probably very, very low it is still a good idea to observe good hygiene and wash
hands and faces after playing with the puppy. Also, Humans should clean vegetables grown in the garden before
eating them. For most people, these preventative measures are just normal procedures but it is good to know
there is a reason for all this caution!
Because pups may start passing eggs as early as day 21 of life, the first treatment must be administered before
this age. Since reinfection is common from the environment as well as in the mother's milk, treatment must often
be repeated every two weeks until the pups are 49 days old. In practical terms, this means treating pups at 2, 4, 6,
8 and 10 weeks of age. Bitches should be treated at the same time as the pups since they are most often the source
of the pups infection. All bitches should be presumed to be carriers of roundworms even if they have had negative
fecals prior to whelping since the worms often persist in her system in a resting stage. The following list discusses
how bitches carry roundworms and infect pups before they are even born:
Roundworm larvae migrate to somatic tissue (liver and lungs), including skeletal muscle and remain there in a
quiescent state Only resume activity in pregnant bitches following the 42nd day gestation (third trimester)
May establish an infection of the small intestine by tracheal migration Usually infect the fetus via the umbilical vessels; initially they attack the pups liver, then lungs at birth This is the primary reason that bitches should be wormed before breeding, during the last week of gestation, and each time the pups are wormed.
Once the initial infection is treated properly it is a good idea to occasionally check a stool sample for the
presence of worms or to consider prophylactically administering deworming medications if the situation seems
to warrant it. It is hoped that at some point in the future a vaccine will become available for roundworm control
since current control measures seem to be only marginally effective. For the present however, routine treatment
of pups and bitch, as well as environmental control are necessary.
Tapeworms
Tapeworms (Taenia pisiformis, Dipylidium canium, Enchinococcus granulosus, and Echinococcus multilocularis)
are found in the intestine of dogs and are a major hygienic concern because they are transmissible to people. Dog-
rabbit tapeworms (T. pisiformis) have a life cycle that starts with them living in the small intestines of wild foxes,
coyotes, and wolves where they produce eggs that are shed in the feces and subsequently contaminate the local
environment. Rabbits then become infected by ingesting these eggs which then form hundreds or even thousands
of "hydatid cysts" in the tissues. When dogs or their wild cousins eat these rabbits they can be infected with
hundreds to thousands of adults. These adults latch onto the wall of the intestines and after about a month, start
shedding eggs. These eggs are then immediately infective to other animals, including people. To complicate matters
further, these tapeworm eggs can remain infective in the environment for several months.
Infected dogs may seem clinically normal while shedding large numbers of infective eggs. The eggs are
generally first seen in your dog's feces or sticking to the hair around your dog's rear. These specialized muscular
egg cases are actually segments of the worm that are full of eggs and they look like a small, flattened, grain of
white rice that moves. As the egg case wiggles around it is spreading thousands of tapeworm eggs which are too
small for the naked-eye to see.
Adult tapeworms appear to cause very few clinical problems in dogs. However, this is the real point of concern
since infected people are not as lucky. Alveolar hydatid disease in humans, caused by Echinococcus multilocularis,
is a very serious infection that usually involves the liver. Early in the course of the infection, patients may be
misdiagnosed with other liver ailments. Involvement of other tissues, including the lungs and brain can also occur.
Since over 50% of people with alveolar hydatid disease die, this is considered the most lethal worm infection that
people get. It is therefore important for all dogs and cats in high-risk areas be screened for tapeworm infection.
This is more difficult than it sounds since infection with Echinococcus eggs can not be readily differentiated from
the more common tapeworms which do not affect people. Veterinarians finding tapeworm eggs on fecal exams
usually closely examine pets for the rice-like grains known as proglottids which are found with common tapeworms
but not the lethal variety. Occasionally more dramatic methods are necessary to try to recover worms from suspect
pets. A more convenient blood test is available to diagnose infection in people and hopefully similar tests will soon
become suitable for pets.
The best defense is increased public awareness of this condition. Personal protection and hygiene are important,
especially to those individuals that may contact feces from potentially-infected pets. Children are particularly at risk.
Mulch that contains feces from dogs, cats, wolves or foxes should not be used on gardens.
Fortunately for pets, there are medicines that are safe and very effective for treatment. People are not as lucky
and surgery still remains the preferred treatment.
In conclusion, Echinococcus multilocularis, may cause a mild problem in pets but if people get infected, the results can be fatal. In order to minimize the risk of human infection the public must increase its awareness of the potential complications that are associated with the parasites.
Whipworms
Surveys consistently identify whipworms (Trichuris vulpis) as one of the most common parasitic worms of dogs
in North America, while only infrequently being reported in cats or humans. They live in the lower aspects of the
intestines (the cecum and colon) where they latch on to feed. Sometimes they cause no problems at all but they
may cause abdominal upset (colic) or diarrhea, often tainted by blood and mucus. When eggs are laid in the
intestines, they pass into the feces and become infective within 9-10 days. When consumed by dogs the infective
eggs hatch in the intestines and the larvae parasitize the intestines and matures further.
Many people do not realize that dogs do not begin to shed whipworm eggs in their stool until about 3 months
after being infected. At that time each female whipworm may pass from 1000 to 4000 eggs per day into the stool.
Complicating matters further are that female whipworms are long-lived, surviving for months or years in the
intestines. The life cycle therefore includes a larval stage in the small intestine, an adult stage in the large
intestine, and infective eggs that pass into the feces.
Diagnosis is not always easy since it depends on finding whipworm eggs in the feces. Remember that animals
are infected for 3 months before they begin to shed eggs and you can appreciate the problem. Once females begin
shedding eggs, they are usually recoverable by direct smears and centrifugal flotation. They are not as easily found
with standard fecal evaluations. In some instances, the adult worms are actually seen attached to the lower bowel
during endoscopic procedures.
Treatment is also not straightforward because of the peculiar life cycle of this parasite. Although many medicines
are effective in removing adult worms, the larvae are less reliably cleared. Therefore treatment must often be
repeated in 3 weeks and often, in 3 months as well, when the larvae have evolved into egg-producing adults. The
biggest hindrance to effective treatment is that animals are often re-exposed to environments in which whipworm
eggs are plentiful, and are thereby re-infected.
It can be difficult to control exposure to whipworm eggs on lawns or soil but concrete can be effectively
disinfected. Proper disposal of egg-containing dog feces is critical.
Hookworms
There are four species of hookworms that infect dogs (Ancylostoma braziliense, Ancylostoma caninum,
Ancylostoma tubaeforme, and Uncinaria stenocephala). In dogs, A. caninum is the most common hookworm
and causes the worst disease. A. tubaeforme is more common in cats than dogs, and is less likely to cause
severe disease than A. caninum. Dogs in the Northern states and in Canada are more likely to be infected
with U. stenocephala as it prefers cold climates and A. caninum prefers warm climates.
A. caninum hookworm infestation in dogs can lead to severe anemia, especially in puppies. These hookworms
have big appetites and attach to the intestine and feed on the dog's blood. The other three types of hookworms are
less likely to cause severe anemia but it is a potential problem with them. Signs of hookworm infection include
weight loss, pale color, black or tarry looking stools, weakness, anemia and death. In areas in which hookworms
are prevalent there can be skin disease in pets associated with exposure to the larval worms as well. The
following are a list of clinical signs of hookworm infestation in canines:
Dose, age, immune status dependent; may be severe and life-threatening
Primarily a disease of puppies, since adult dogs exposed as puppies have a premune status due to presence of
arrested larvae Dermatitis Puppy pneumonia Enteritis, bloody diarrhea, blood loss anemia Life threatening for
pups - may show signs as early as 2 to 3 weeks of age in a peracute case (puppy crashes without prior signs of disease) or may occur in an acute stage at 3 weeks to weaning where there are eggs in the feces, bloody stool Hookworms can be acquired from the mother's milk, from penetration of the skin by hookworm larvae in the
environment and from eating hookworm larvae. Some vets think that it may also be transmitted during pregnancy
from mothers to puppies but this is controversial.
One of the problems with hookworms is that they can accidentally infect humans. This creates a problem called
cutaneous larva migrans, which loosely translates to worms migrating through the skin. Humans pick up the
hookworm larvae from areas contaminated by dog feces and they penetrate the human's skin just like they would
the dog's. Since they don't belong in the human they don't develop into adults but just migrate around in the skin,
causing sores and inflammation, until they die. This is a good reason to keep dogs and cats from defecating in
playground areas, beaches and other places where people's skin is likely to come in contact with the ground.
Fortunately, the monthly heartworm preventatives are also effective at controlling hookworms and can provide
a measure of protection against the possibility of the cutaneous larva migrans syndrome occurring in the humans
that own dogs and cats on heartworm preventative medications. In areas in which heartworms are not a problem
but hookworms are, it is a good idea to consider having a pet's stool examined for the presence of worm eggs
once a year and when clinical signs that may indicate infestation occur.
