Intestinal Parasites: The Squirm-Worthy Side of Living With Dogs

Picking up dog poop
You help prevent the spread of intestinal parasites by promptly picking up your dog's poop after he goes.

The woman dangled the plastic bag, pinched between the tips of her forefinger and thumb, at arm’s length over the clinic counter. “I agreed to a puppy, but I didn’t sign up for this,” she said dramatically. Through the clear plastic, I spotted roundworms wriggling in the stool sample.

Maybe it’s not the most appealing mental image, but it is a good reminder of why you should take parasite prevention seriously. Especially since worms aren’t just for puppies: Adult dogs and even human family members can get them, too. Here’s what you need to know about these common intestinal parasites and what you and your veterinarian can do to help prevent them.


Nothing’s more adorable than a puppy with a big, round Buddha belly, right? It’s not so cute once you know it could be a sign of a roundworm infection. Many puppies get roundworms from the mother before they’re born or become infected when nursing.

Puppies and dogs can also get roundworms from ingesting infective eggs in the environment or from eating infected mice, rabbits and earthworms. Once in the body, the eggs hatch releasinglarvae that can migrate throughout the liver and lungs, and eventually return to the intestines, where they grow into adults. Adult worms produce eggs, which are passed in the stool into the environment.

Not every dog with roundworms will show signs. But large infections, especially in puppies, can result in vomiting and diarrhea (sometimes with visible worms), failure to gain weight and even death.

Roundworms are considered zoonotic, meaning they can be passed from dogs to humans. People can get roundworms by inadvertently ingesting infective eggs from contaminated soil, and children are especially at risk. In people, roundworm infection can cause damage to the eyes, liver, lungs and nervous system.


Hookworms use their sharp teeth to attach to the lining of the small intestine, where they live off your dog’s blood. Severe infections in puppies can lead to anemia (an inadequate number of red blood cells), typified by pale, whitish gums, and even death. Other dogs may cough, have diarrhea, bloody or black stools — or have no obvious signs at all.

Puppies can get hookworms when they nurse an infected mother. But how does your adult dog become infected? If a dog with hookworms visits the dog park (or any other public place -- or even your own yard), eggs can be passed in his feces, contaminating the grounds. There, the eggs hatch into larvae, which can penetrate your dog’s skin or be ingested. Your dog can also get hookworms from eating infected prey or cockroaches.

Once in the body, the larvae can travel through the lungs and other tissues to the small intestine where they develop into adults. Hookworms can live in the intestine for up to two years, and an adult female worm can produce up to 6,000 eggs per day.

If that’s not disgusting enough, consider that hookworms are happy to invade people, too. All you have to do is walk barefoot, sunbathe or picnic on contaminated ground, or garden with your bare hands in contaminated soil, and hookworm larvae can penetrate your skin. In people, hookworms can cause a skin condition where the larvae leave red, itchy tracts, where they travel under the skin, or severe abdominal pain.


These tiny worms usually live in your dog’s cecum (a pouch at the beginning of the large intestine) and sometimes in the colon. They thread themselves into the intestinal lining, which can bleed and become inflamed. Dogs with whipworms rarely show signs, but severe infections can lead to diarrhea with mucus or blood, weight loss and death.

Dogs become infected with whipworms by ingesting infective eggs in their environment, such as contaminated soil. Unlike the other worms mentioned here, whipworms don’t migrate throughout the body, rather they remain in the digestive tract. A female whipworm can produce up to 2,000 eggs per day. Thankfully, this is one intestinal worm that rarely infects people.


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