Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

University of Illinois at Urbana-Champaign

U of I logoCollege of Veterinary Medicine

Back to search page.

Common Internal Parasites of Pets

Pet Column for the week of January 17, 1994

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
By Linda March
Information Specialist

You are armed and ready; leash and collar in place on your dog, and "baggy" in hand, out
you go to collect a fecal sample.

If you feel awkward about bringing a stool sample to your veterinarian, you are probably
not alone, but it is nevertheless a very important tool for detecting internal parasites. By
identifying microscopic eggs in the feces, the veterinarian can choose a proper treatment for
the parasite infecting your animal.

One of the most commonly seen intestinal parasites in dogs is roundworms (Toxocara
canis), according to Dr. Allan Paul, small animal Extension veterinarian at the University of
Illinois College of Veterinary Medicine at Urbana. "Puppies can be born with them; they get
the parasite while still in their mother's uterus," he says. "They can also get roundworm
through mother's milk, ingesting contaminated feces, or by eating a transport host, such as a
rodent that has been infected with roundworms."

Adult dogs with roundworms do not usually show any signs. If they do, it is generally
vomiting or diarrhea. Puppies will have a rough hair coat and a "pot belly". They may also
have diarrhea and vomiting episodes.

Cats may also become infected with roundworms and show similar signs of vomiting and

Hookworms (Ancylostoma, Uncinaria spp.) are another common pet invader. These
worms penetrate through an animal's skin, are ingested in the larval form, or are passed
through the mother's placenta or milk. Hookworms are blood feeders. They attach to the
animal's small intestine and leave bleeding sores. Therefore, hookworms may cause anemia
and black feces in your pet. "They can cause enough damage to be lethal in puppies," notes
Dr. Paul.

There are two common types of tapeworm in pets. One type, Dipylidium caninum is spread
when a pet ingests fleas. The other type, Taenia, is spread when the animal eats an infected
rodent or rabbit. Both types of tapeworms produce segments that pass out of the animal's
rectum. When dry, the Dipylidium caninum segments look like "cucumber seeds", and the
Taenia segments look like "rice grains." These egg packets may be seen on the pet's anal
area and in their bedding. Though tapeworms don't cause physical damage like
hookworms, they do with the pet for the nutritional value of its food, causing an unthrifty
appearance and rough hair coat.

Whipworm (Trichuris vulpis) is a worm that attaches to the large intestine or cecum (a blind
sack where the small and large intestine join). This worm may cause chronic diarrhea with
red blood in the stool, anemia and a general unfit appearance in dogs. It does not infect

Since many intestinal parasites may be transmitted by oral-fecal contact, sanitation is a key
part of control. Keep your pet's living quarters as free of feces as possible to reduce the
chances of infection.

Dirofilaria immitis, commonly known as heartworm, is a potentially lethal internal parasite in
pets. "It usually infects dogs, but has also been found in cats," notes Dr. Paul. Mosquitoes
infect pets by biting them. The larval form of the heartworm migrates in the pet's body for
about six months and finally stops in the heart when the worm becomes an adult. Your
veterinarian must draw a blood sample and test it to detect the presence of heartworm.

The animal usually doesn't show signs of infection until late in the disease process. It may
develop a dry, nonproductive cough and tire easily even if only given light exercise.

There are monthly or daily medications available for heartworm prevention. You and your
veterinarian can decide which one best fits your lifestyle.

Treatment of heartworm disease is available, but it is risky.

Heartworm testing needs to be done annually, preferably before mosquito season in your
area. Intestinal parasites can be screened for by bringing in a stool sample at the same time.
Some parasites are harder to kill and may require repeated treatment. Your veterinarian can
help you.

Any time your pet develops a rough hair coat, an unthrifty appearance, diarrhea, if you see
segments, or it begins to vomit, see your veterinarian.