Parkway Animal Hospital's


Intestinal Parasites

Dogs and cats can become hosts to many intestinal parasites and a few general statements apply to all parasitic infections:

The following is a brief description of the common intestinal parasites with their symptoms, diagnosis, treatment, prevention, and human transmission.

Image of the life cycle of roundworms

This is a common worm of puppies and kittens, but can be seen in any age dog or cat. Diagnosis is made from a microscopic examination of the feces or from a description of the worm if it is seen in the stool or vomit. Treatment is an oral medication given at 2-week intervals. Symptoms will vary from none to marked vomiting and diarrhea, and abdominal swelling. Transmission to adult dogs and cats occurs by infected feces contaminating the yard. As a result, prevention is accomplished by isolating your pet from infected feces of other animals. For dogs, the heartworm preventives also prevent roundworm infection. Transmission to humans is rare; young children can develop "visceral larval migrans" by eating dirt contaminated with feces.

Photo of roundworms
  • Round; white; 2-4 inches long: may curl up when seen; resemble "spaghetti"
  • May be vomited up from stomach; or coughed up from the lungs.
  • May cause intestinal blockage when found in large numbers.
Drawing of the life cycle of hookworms

This is also a common worm of puppies and kittens but is seen with equal frequency in adults. This parasite sucks your pet’s blood and can cause a severe anemia. Diagnosis is made from a microscopic examination of your pet’s stool. Treatment is either an oral medication or an injection or both. This is repeated 2 weeks later. Symptoms will vary from none to blood in the stool (dark tar-colored stool) with diarrhea. Severe cases may need a transfusion and hospitalization. Transmission to adults occurs by infected feces contaminating the grass or soil. Prevention, therefore, requires that the pet be kept away from contaminated areas. Two types of heartworm preventive can also prevent hookworm infections in dogs Transmission to humans is uncommon and usually shows up as skin lesions.

photo of hookworm
  • Very thin, almost transparent; 1/4 -1/2 inch long.
  • Normally not visible to the naked eye.
  • Hook on to the intestine and suck blood, which causes anemia.
  • The mother may infect puppies through the milk when nursing.
  • May be ingested orally or may actually penetrate the skin (usually through feet).
  • Was a problem in humans years ago when everyone went barefooted most of the time?
  • Causes bloody diarrhea and death when severe.
  • Most harmful of all internal parasites!
Drawing of the life cycle of whipworms

This worm affects dogs only. Diagnosis is also made from a microscopic exam of the feces. Eggs from this parasite pass intermittently, however, so it may be necessary to check multiple fecals before a diagnosis is made. Treatment is an oral or injectable medication given at 3 to 12 week intervals depending on the severity of the infection. Symptoms vary from none to severe watery diarrhea, vomiting, and marked weight loss. Some dogs require hospitalization for treatment of dehydration, malnutrition, and infection. There is no human transmission.

Photo of whipworms
  • Inhabit the lower part of the intestine (colon).
  • Causes chronic diarrhea, sometimes containing blood.
  • Normally not visible to the naked eye.
  • Eggs are ingested off the ground.
Drawing of the life cycle of tapeworms

This common worm affects both dogs and cats. Transmission occurs when your dog or cat bites and "eats" a flea. The intermediate form of the tapeworm is inside the flea’s body and it then attaches to the intestine and begins to grow "segments." In about 3 weeks, these segments begin to pass in the stool. They are approximately ¼ to ½ inch long, flat, and white. After a short time in the air, they dry up to resemble a small yellow flat seed. Diagnosis is made from seeing these segments on the stool or on the pet’s back end rather than a microscopic fecal exam. Treatment is either by oral tablets or by an injection. The tapeworm medication kills existing tapeworms but it does not prevent future infection. The only prevention is strict flea-control. There is no direct transmission from dog or cat to a human.

Photo of tapeworms
  • Short, flat segments (look similar to "rice" or "cucumber seeds").
  • Causes a poor appearance and dry skin.
  • Often seen on the hair around the rectum.
  • Cannot always be diagnosed by microscopic exam like other parasites, unless a segment just happens to be present – segments are not passed every day.
  • Spread by fleas, rabbits, birds, and other rodents – not by dogs and cats.
Drawing of the life cycle of giardia

This parasite is not a worm. It is a very tiny single-celled parasite that can live in the intestines of dogs, cats, and man. It is seen most commonly in dogs coming out of kennel-type situations (pet stores, shelters, dog pounds, etc.) but its incidence is increasing. Symptoms include intermittent or continuous diarrhea, weight loss, depression, and loss of appetite. Diagnosis is made from a very fresh fecal specimen that must be collected at the clinic for optimum results. A surprising number of affected animals are "occult"; that is, they are infected but are negative on these tests even with multiple examinations. As a result, this parasite is often treated without a confirming diagnosis. Treatment is an oral medication administered at home. Prevention involves careful disposal of all fecal material and cleaning contaminated areas. Humans can become infected with Giardia so special care must be taken to wash hands and utensils.

photo of giardia
Photo of a coccidia

This is also a single-celled parasite. It is seen primarily in puppies and kittens, although debilitated adults can also be affected. Transmission occurs by eating the infective stage of the parasite. It then reproduces in the intestinal tract causing no symptoms in mild cases to bloody diarrhea in severely affected pets. Diagnosis is made from a fresh stool sample. Treatment varies greatly. Animals showing no signs of illness are often not treated because a mild case is often self-limiting. Pets with diarrhea are treated at home with an oral medication. Severely affected pets may need hospitalization. Prevention involves disposal of all stools and cleaning the pet’s living area. Human transmission is uncommon but can occur.

Internal Parasite Prevention:

Internal parasites are often grouped together and called "worms." Roundworms, hookworms, whipworms, and tapeworms often infect pets.

The Center for Disease Control (CDC) and the American Association of Veterinary Parasitologists (AAVP) now recommend the routine deworming of pets on a regular basis. This is called "Strategic Deworming," and is designed to prevent parasite disease and the shedding of parasite eggs in your yard and home. This is important because the eggs in the environment as well as the pet can infect members of your family.

Virtually all puppies and kittens are born with internal parasites (worms) or are infected shortly after birth through the mother’s milk. Our practice routinely deworms all new puppies and kittens at least 3 times during our initial preventive care visits.

Roundworms are very common and it is estimated that a female roundworm can produce more than 200,000 eggs daily, which can remain alive in the soil for many years. Roundworms cause "larval migrans" and possibly can result in blindness in humans. It is estimated that 10,000 children in the U.S. are infected annually with roundworms and that approximately 750 will suffer visual impairment or even blindness. Infection occurs when the roundworm eggs from the environment are ingested, usually from accidentally putting dirty hands in the mouth. Fruits & vegetables growing close to the ground, such as strawberries & carrots, may be contaminated.