Intestinal Parasites

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

  • All deworming medication can be poisonous if given improperly and should only be used as directed.
  • There currently is no medication that is capable of eliminating all species of parasites. Consequently, an accurate diagnosis is necessary to properly treat your pet.
  • Diagnosis is usually made from a fresh stool sample (passed less than 12 hours before). Tapeworms can be diagnosed by observing segments in the stool, which look like small grains of rice.
  • Most puppies and kittens are infected before birth and, for this reason, they need dewormed starting at 6 weeks of age. If hookworms are suspected, stools should be checked starting as early 2-3 weeks.
  • Occasionally, for heavy parasitic infections 3 or even 4 treatments may be necessary to eliminate the parasite.

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


Roundworms are a common parasitic worm of puppies and kittens, but can be seen in dogs and cats of any age. Adult roundworms are round, white, and up to four inches in length. They can sometimes be seen in feces or vomitus, and even be coughed up from the lungs. Some pets will display symptoms including vomiting, diarrhea, and abdominal swelling, where others might not show any sign of infection. If the worms become present in large numbers, they can actually obstruct the intestine and surgery may be required to unblock it. Transmission to adult dogs and cats occurs by coming into contact with infected feces. Diagnosis is made by using a microscope to find eggs in the feces. To treat this parasite, an oral medication is given in two week intervals. The best way to avoid a roundworm infection is keeping by keeping your pet away from other animals’ stools. In addition, many types of monthly heartworm preventives also treat roundworms. Transmission to humans is rare; young children are the most likely to develop “visceral larval migrans” by ingesting dirt or sand contaminated with roundworm eggs. Visceral larval migrans is characterized by the immature roundworm’s migration from the intestine to other organs of the body, including the heart, liver, brain, and eyes.  The disease can be avoided by making sure your pet defecates far away from where your children play and promptly cleaning it up.

Roundworm Life Cycle


Hookworms attached to the intestinal wall

Hookworms are small, blood-sucking worms that attach to the intestinal walls of dogs and cats and can cause severe anemia.  They are actually considered one of the most harmful internal parasites of pets. The adults are a half inch long, very thin, and almost transparent. The most common sign of infection is diarrhea containing blood. Heavy infections can be fatal. Hookworms can infect adult pets through ingestion of the infective larvae. Alternatively, infective larvae can penetrate an animal’s skin and migrate through the tissues to the small intestine. This occurs when an animal walks through soil or grass contaminated with the parasite. Puppies and kittens generally acquire the infection from their mothers’ milk. Like roundworms, diagnosis is made through microscopic analysis of stool and is treated with an oral medication in two-week intervals. Also, many heartworm medications act as  hookworm treatment. Humans can develop “cutaneous larval migrans” when bare skin comes into contact with hookworms larvae, characterized by red, painful lines on the skin. This is caused by larvae burrowing into the skin to enter deeper tissues. Cutaneous larval migrans can be avoided by wearing shoes or sandals in areas that might have a hookworm contamination, such as outdoor kennels, dog parks, and beaches.

Hookworm Life Cycle


The canine whipworm is a common parasite of both dogs and puppies, but the feline whipworm is extremely rare in North America. The adults inhabit the large intestine and are not normally visible to the naked eye. Symptoms include weight loss, vomiting, and chronic diarrhea, sometimes containing blood.  Dogs with severe infections might need to be hospitalized for treatment of dehydration, malnutrition, and infection. In rare cases, whipworm infections can cause rectal prolapse, which is when walls of the rectum protrude through the anus and hence become visible outside the body. Contraction occurs through the ingestion of eggs off the ground. Animals often become reinfected with whipworms if confined in contaminated environments because the eggs are very resistant to weather hazards. Oral medication is given in 3 to 12 weeks intervals to treat infections. Diagnosis is accomplished through microscopic analysis of feces. However, hookworms shed their eggs intermittently and several fecal checks may be required to obtain a diagnosis. The canine whipworm cannot be transmitted to humans.

Whipworm Life Cycle


Tapeworms are a very common parasite in Rock Island that affects both dogs and cats. It can be contracted through the ingestion of an immature tapeworm in birds, rabbits, rodents, and most commonly, fleas. Once inside a dog or cat, the tapeworm matures and attaches the intestinal wall. It begins growing in segments and, depending on the species, can reach a length ranging from a few millimeters to hundreds of centimeters. Segments are shed periodically and pass in the stool. These segments contain several “egg packets” and must be eaten by an insect or crustacean in order to continue development. Insects and crustaceans serves as intermediate hosts, and they need be consumed by another intermediate host or a final host, such as a dog or cat, to complete their life cycle. Diagnosis of a tapeworm infection is generally accomplished by observing segments within the feces or around the anus. They are usually elongated, white, less than a centimeter long, and resemble grains of rice. After being exposed to air, they dry up to resemble small, flat seeds like those of a cucumber. The right oral medication used three-weeks apart can successfully eliminate a tapeworm infection. Tapeworms can be avoided by making sure your pet does not eat wildlife, but the best prevention from tapeworms is strict flea control. There is no direct transmission of tapeworms from pets to humans; however, if tapeworm segments of certain species are ingested by a human, they can hatch and form cysts in the liver, brain, or other organs. Humans can also contract small tapeworms from swallowing a flea infective with an immature tapeworm. Be sure to always wash your hands after disposing of animal waste and keep children away from animal feces.

Tapeworm Life Cycle


Scanning Electron Micrograph of Mature Giardia

Giardia is a single-celled parasite that resides in the small intestine of cats, dogs, and humans. A recent survey suggests that 15% of dogs and 10% of cats in the United States are infected with Giardia, and its rates of infection are increasing. Pets can become infected with this parasite by drinking water contaminated with Giardia cysts, the infective stage of the parasite. Water becomes contaminated through the feces of an infected animal. The disease caused by the parasite is referred to as giardiasis and is most commonly seen in dogs coming out of kennel-type situations, such as pet stores, shelters, and dog pounds. Symptoms include intermittent or continuous diarrhea, weight loss, depression, and loss of appetite. There are several methods currently for diagnosis of giardiasis, though the most common is fecal analysis. Giardia is a often times a very difficult parasite to diagnose because of its small size and intermittent shedding periods of cysts. The mature parasite and cysts can be located in a fresh fecal sample, though the procedure may need to be repeated several times to insure an accurate diagnosis. Treatment is accomplished with an oral medication used for 5 days. Reinfection is common so be sure to clean your pet’s rear and paws after it use the litterbox or yard and immediately dispose of any waste. Human transmission is possible, so make sure to thoroughly wash your hands afterward.


Coccidia are another single-celled parasite, most commonly seen in puppies and kittens, although debilitated adults can also be affected. Transmission occurs through ingestion of the infective stage of Coccidia. 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. Animals showing no symptoms are often left untreated because mild cases can be self-limiting. Pets experiencing coccidia-related diarrhea can be treated with a oral medication. In rare cases, hospitalization may be needed. Prevention includes proper disposal of stool and regular cleaning of the pet’s living area. Human transmission is uncommon but can occur.

Comments are closed.