Intestinal parasites in cats and dogs

What are roundworms and how are they spread?

Roundworms are common in cats and dogs. They get their name from their tubular bodies. Infected animals pass roundworm eggs in their feces (poop). Your pet can catch roundworms by swallowing these eggs in feces-contaminated soil or water, or by licking contaminated fur or paws.

Once inside the body, the eggs hatch, releasing larvae that move through the lungs and liver and eventually settle in the small intestine. There, they grow to adult worms and mate, producing eggs and continuing the infection cycle. Roundworm infections usually peak during the winter and decrease over the summer.

Puppies and kittens are especially prone to roundworms. Infected female dogs may pass the parasite to their puppies before birth or through their milk when puppies are nursing. Infected female cats cannot infect their kittens before birth, but can pass on the infection through their milk.

Roundworm health risks to pets and people

Adult roundworms steal nutrients from the food that pets eat. This can cause poor nutrition and intestinal problems. In young animals, roundworm larvae also can cause serious respiratory problems like pneumonia as the larvae move through the lungs.

Roundworm infections are zoonotic, meaning that they can be transmitted to people. Most human infections come from accidentally swallowing roundworm eggs. Children, especially those who eat dirt, are at particular risk.

Unlike in pets, roundworm larvae in people travel to organs like the liver, lungs, and brain, and settle there, never becoming adult worms. While most infected people will have no symptoms, those unable to fully fight the infection—such as young children, the elderly, and people with weakened immune systems—may develop lung, brain, liver, or eye damage.

What are hookworms and how are they spread?

Hookworms are common in dogs, and cats are susceptible too. These parasites get their name from their hook-like mouthparts. Infected animals pass hookworm eggs in their feces, which then hatch in the environment to release larvae.

Your pet can become infected by swallowing larvae in feces-contaminated substances or by eating an infected animal or insect. Direct contact with the larvae also can cause infection if they penetrate your pet's skin. An infected female dog can pass the parasite to her puppies through her milk, but this does not occur in cats.

Once an animal is infected, hookworm larvae travel through their body. Larvae that make it to the small intestine attach themselves there, where they grow into adult worms and produce eggs. Unlike roundworms, hookworm infections peak in the summer and fall.

Hookworm health risks to pets and people

Hookworms are dangerous because the adults actually bite into the intestinal lining of an animal and suck blood. Puppies and kittens are at high risk of becoming infected and developing severe disease. Left untreated, hookworm infections can cause weakness, poor nutrition, and potentially life-threatening blood loss.

Hookworms also can infect people if the larvae are swallowed or penetrate the skin—for example, when someone is walking barefoot on contaminated soil or sand. Swallowed larvae can cause intestinal and other problems in people. Larvae that penetrate the skin can cause severe itching and tunnel-like, red areas.

What are whipworms and how are they spread?

Whipworms get their name from their whip-like shape. Infection is much more common in dogs than in cats. Infected animals (mostly dogs, foxes, and coyotes) pass whipworm eggs in their feces. Your pet can catch whipworms by swallowing whipworm eggs in feces-contaminated soil or by licking contaminated fur or paws. Infections tend to peak in the winter.

Whipworm health risks to pets and people

Adult whipworms thread themselves into the lining of an animal's intestine and eat blood and tissue. Although this may sound serious, whipworms usually do not cause health problems in dogs or cats. Occasionally, severe infections can occur, causing diarrhea, weight loss, blood loss, or even death.

The risk of pets spreading whipworms to people is considered low.

What are tapeworms and how are they spread?

Tapeworms get their name from their long, thin, flat appearance, like strips of tape. Dogs and cats become infected with certain types of tapeworms when they swallow fleas or lice infected with tapeworm larvae. This happens most often when the dog or cat is grooming. Your pet also can catch certain types of tapeworms by eating infected rodents.

Tapeworm health risks to pets and people

Adult tapeworms live in the small intestine, but rarely cause disease. Infection is usually diagnosed when egg-containing tapeworm segments are seen under the pet's tail, in their feces, or on their bedding. These segments look like flattened grains of rice or cucumber seeds, and could be mistaken for maggots or fly larvae. Only rarely are these types of tapeworms a risk to people.

Coccidia

Coccidia are microscopic, single-celled parasites. Dogs and cats are susceptible to certain types of coccidia, which are broadly known as Cystoisospora. Like other intestinal parasites, coccidia can be passed by infected animals in their feces. Your pet can become infected by swallowing feces-contaminated soil, food, or water, or by licking contaminated paws or fur.

Once swallowed, coccidia damage the lining of the intestines and interfere with absorption of nutrients. Infected animals may have loss of appetite, abdominal pain, diarrhea (which may contain blood), dehydration, and weakness. However, these signs don't always occur, and some infected animals may seem healthy.

Puppies and kittens are particularly susceptible to coccidia infection and severe illness because they have no immunity to the parasite. This means that the infection is highly contagious to other puppies and kittens.

The types of coccidia that infect dogs and cats are not known to infect people.

Giardia

Giardia are also single-celled parasites that, if swallowed, can damage the lining of the intestine and reduce nutrient absorption. They too are passed in feces. Your pet can catch Giardia through the same routes as coccidia. Infected animals may have diarrhea (persistent or on-and-off) and/or greasy (fatty) feces, excess gas, and weight loss, while others may seem healthy.

The strains of Giardia that infect dogs and cats do not usually infect people.