605 West 5th Street

Morris, MN 56267 US



Internal Parasites

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

  • All deworming medicines are poisonous to some extent and should only be used as needed and under proper conditions.
  • An accurate diagnosis is necessary to treat your pet properly. Diagnosis is usually made from a fresh stool sample (passed less than 12 hours) or, in the case of tapeworms, seeing the segments in the stool.
  • Puppies and kittens may be infected before birth and, for this reason, will need deworming starting at 6-8 weeks of age. If hookworms are suspected, fecal examinations should be done starting as early as 2-3 weeks.
  • Occasionally, for a heavy parasitic infection, 3 or even 4 treatments may be necessary to eliminate the parasite.
  • The following is a brief description of the common intestinal parasites with their symptoms, diagnosis, treatment, prevention, and human transmission.


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- 4 week intervals. Symptoms will vary from none to 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.

  • 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.


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 -3 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.

  • 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).
  • Causes bloody diarrhea and death when severe.
  • Most harmful of all internal parasites!


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.

  • 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.


This common worm affects both dogs and cats. Transmission occurs when your dog or cat bites and ingests 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 hair around the pet's rectum rather than a microscopic fecal exam. Treatment is either by oral tablets or liquid. 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.

  • 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.


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.


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

  • Fecal examination of your pet's stool.
  • Use specific wormers for the type of parasite present, as determined by microscopic fecal examination.
  • Remove feces from your lawn, street, or kennel daily.
  • Exercise your pets in grassy areas not frequented by other animals.
  • Prevent your pet from eating rodents, such as mice, rats, and rabbits.
  • Control fleas!
  • Treat females before breeding, and again before whelping to help prevent infecting newborn pets.

Strategic Deworming
Many puppies and kittens are born with internal parasites (worms) or are infected shortly after birth through the mother's milk. Deworming new puppies and kittens at least twice during initial preventive care visits is recommended

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