Roundworms, tapeworms, coccidia—any number of parasites can infect your dog or cat’s intestinal tract, and some can be transmitted to humans. Learn which parasites are lurking in the environment so you can recognize clinical signs and prevent infection in your pet.

Roundworms in pets

Roundworms are the largest intestinal parasites of dogs and cats, and look like long spaghetti strands. Roundworms remain dormant in adult animals, but reactivate when the dog or cat is pregnant, allowing transmission to most puppies and kittens. Several doses of a deworming medication should be administered to puppies and kittens starting at 2 weeks of age.

Puppies with roundworm infections may fail to gain weight, and have a dull hair coat and a potbelly. They may vomit worms, which are sometimes seen in their feces. Occasionally, a large worm burden can obstruct the intestines and cause death. Adult pets can contract roundworms by ingesting eggs shed in the feces of infected animals, or by eating infected rodents; however, adults rarely show clinical signs. Roundworms can infect people, and human infections are most common in children who play in the dirt or sand where animals defecate.

Hookworms in pets

Hookworms are tiny worms with hook-like mouths that they use to attach to the pet’s intestinal wall and then ingest blood. Hookworms can also lie dormant in adult dogs and cats, and can be transmitted to puppies and kittens via milk; however, infections are not as common as roundworms. Hookworm infections can cause weight loss, decreased appetite, diarrhea, weakness, and anemia from blood loss. Adult pets can be infected by ingesting eggs shed in feces, ingesting rodents, or by skin penetration of larval worms in the environment. Larval worms can also infect people through skin penetration, and infections are most likely in people who walk barefoot outdoors. 

Whipworms in pets

Whipworms are tiny worms that live in a pet’s large intestine, where they latch onto the intestinal wall and ingest blood. Infections are seen mainly in dogs, with transmission through ingestion of infective eggs passed in the feces. Light infections often cause no illness, but heavier infections can cause weight loss, diarrhea, and anemia.  

Tapeworms in pets

Tapeworms are long, segmented worms that attach to the intestinal lining and absorb nutrients from their host. Infection rarely causes clinical signs, although weight loss, lethargy, and mild diarrhea are possible. Worm segments, which look like rice grains or sesame seeds, break off and are shed in the feces, and can often be seen in the feces or stuck to the hair around the anus. Dogs and cats contract tapeworms by ingesting fleas while grooming, or by ingesting small animals, such as rodents. Although some tapeworm species can infect people, the types that infect dogs and cats do not cause human infection.

Giardia in pets

Giardia lamblia is a microscopic, single-celled, motile organism that can cause significant intestinal illness in many pet species. Infected pets often experience lethargy, decreased appetite, vomiting, diarrhea, and dehydration. Giardia organisms are shed in the feces of infected pets and wildlife, and often contaminate ponds and lakes. Pets contract the parasite by ingesting infective cysts passed in the feces or by drinking fecal-contaminated water. People can contract Giardia infections; however, the organism that causes human disease is thought to differ from the organism that causes pet illness. 

Coccidia in pets

Coccidia are single-celled parasites that commonly cause intestinal illness in kittens and puppies. Coccidial infections cause vomiting, diarrhea, lethargy, decreased appetite, and dehydration in affected pets. Infective organisms are shed in the feces, and can be ingested from the environment or by eating wild animals. 

Preventing intestinal parasites in pets


Keeping your pet parasite-free is important to her health, and yours. A parasite-prevention plan includes:

  • Early deworming — All puppies and kittens should be routinely dewormed starting at 2 weeks of age, and continuing through 6 months.
  • A yearly fecal analysis — Your pet’s annual wellness exam should include a microscopic evaluation of her feces for parasite eggs.
  • Regular parasite prevention — Some monthly heartworm preventives also contain medications to prevent other common intestinal worms.
  • Regular flea prevention — Use a veterinary-recommended flea medication to prevent tapeworm infection in your pet.
  • Cleaning up feces — Pick up feces in the environment to prevent egg transmission to your pet or other pets.
  • Preventing rodent ingestion — Keep your pet from eating parasite-carrying small animals, such as rodents.

If you have questions about intestinal parasites or parasite prevention for your pet, contact us.