Common Intestinal Parasites in Cats and Dogs

Roundworms (Ascarids)

Both cats and dogs can be infected by roundworms. They acquire them by ingesting soil/feces contaminated by eggs and larvae or by eating infected rodents, birds and insects. Puppies and kittens are often infected by the mother while still in the uterus. They can also be infected while nursing. Diagnosis can be made by finding eggs by microscopic exam of the feces or by seeing adult worms voided in the feces or vomit. Larval forms can migrate through the lungs and cause a condition known as verminous pneumonia. Adult roundworms live in the small intestines and can form in large enough numbers to cause intestinal blockage and death. They can also be transmitted to people and cause a serious illness known as visceral larval migrans and blindness caused by ocular larval migrans.


Hookworms are a serious parasite of cats and dogs. Pets acquire them by ingesting infective larvae or by the actual penetration of larvae through their skin or feet. They can also be transmitted by the mother during pregnancy or through nursing. These parasites can only be found by microscopic exam of feces. Hookworms attach to the intestinal lining and feed off the blood of their host. They can cause severe enough anemia to cause sudden collapse and death, especially in young, weak and malnourished animals. Other animals may show a slowly progressive wasting disease. Weight loss, diarrhea and tarry or bloody stools frequently occur in animals with hookworms. Hookworms can also be transmitted to humans and cause a skin disorder known as cutaneous larval migrans or creeping eruption.


Whipworms are small, thin worms that live in the large intestine and cecum of dogs. It is extremely rare in North American cats. Dogs acquire them by ingesting eggs from contaminated soil/feces. These eggs are very resistant and can live in the soil for 5-7 years. Infection can only be detected by microscopic exam of the feces. Eggs are shed in low numbers, thus, it may take several stool sample exams to be detected. This can make diagnosing a whipworm infection difficult. Whipworms can cause diarrhea, bloody stools, weight loss and poor general health. Massive rectal bleeding occasionally occurs. Severe infection can result in electrolyte imbalances that will mimic a life-threatening endocrine disease condition known as hypoadrenocorticism.


There are several species of tapeworms. Both cats and dogs can be infected. The most common routes of infection are by eating small rodents/rabbits or by ingesting fleas which carry the infective stage. Tapeworms live in the small intestine with their head buried in the lining. They are relatively harmless to your pet, but can cause mild GI upset on occasion. Tapeworms can be difficult to diagnose on fecal exams as the eggs are often passed in the packets (segments). These segments can be seen in your pets feces or coming out from the anus. They usually are passed as short, flat, whitish objects around ΒΌ-1/2" long. They will also sometimes stay connected and appear as a long, flat ribbon-like object. They will be moving if still alive. Dried out segments appear as yellow-gold rice like objects attached to the hair around the anus. People should not mistake maggots for tapeworms. Maggots are rounded and are not seen in freshly passed stool. Humans cannot acquire tapeworms from their pets. They can, however, acquire them by the same routes as their pets.


Coccidia are single celled organisms that infect the intestines of dogs and cats. They can only be detected by microscopic exam of your pet's feces. Your pet becomes infected by ingesting contaminated dirt/feces or intermediate hosts such as mice. This parasite is especially common in young and stressed animals. It causes bloody, watery diarrhea and sometimes death, especially in young animals. There are no products to kill the organism. Treatment is aimed at stopping reproduction of the organism so it is easier for the patient's immune system to take over and fight off the infection. Treatment usually lasts several days to weeks.


Giardia is a protozoal (one-celled) organism that parasitizes the small intestine of dogs and cats. It can also infect humans. Pets/people are infected by ingesting the cyst form of this organism from contaminated food and water. Diagnosis is made by microscopic exam of feces. It can be very difficult to detect. Symptoms of disease are chronic soft stools to profuse watery diarrhea. There is often mucous mixed in. Weight loss, lethargy, dehydration and anorexia may also occur. Treatment can be difficult as there is a high degree of recontamination of the patient and resistance to several drugs. Bathing the animal during treatment is recommended to help prevent reinfection by your pet licking cysts off of its fur while grooming. While possible, it is very rare for people to contract giardia from their pets.

Physaloptera (stomach worms)

Stomach worms are parasites of both cats and dogs. As the name implies, they live in the stomach. They are often treated for by your veterinarian if your pet has chronic vomiting. Eggs are not readily detected on routine fecal exams. Your pet may occasionally vomit up a worm. Pets are infected by eating an intermediate host such as a cricket, cockroach or another animal which has ingested one of these insects. These parasites are also sometimes diagnosed by endoscopy. These parasites are not infectious to humans.

*You will get better fecal results by submitting fresh stool samples (less than 24 hours old). They should be kept refrigerated but not frozen.

**There is not one dewormer that will control all intestinal parasites. It is important that stool samples be checked frequently and that you consult with your veterinarian on the best treatment for your pet.