The information in this article has been reviewed and updated.

Gastrointestinal (GI) parasites can make your dog or cat — and sometimes even you — sick, which is why it’s so important to prevent infestations, and, if they do occur, to treat your pet quickly. Here are some of the things you need to know to keep your pets safe.

Even the cleanest, best cared-for pets are susceptible to these bugs, which take up residence in the stomach or intestines. Some of these parasites can be spread from mother to puppy or kitten or by fleas or rodents or through the feces. Good hygiene, regular visits to the veterinarian, preventive medicines and deworming treatments can keep your pets free of these pesky intruders. Luckily, if your pet is infected, many effective treatment options are available. Your vet can guide you on what is the best strategy for your pets.

Know The Major Culprits — Roundworms, Hookworms and More

Some GI parasites are big enough that you can actually see them; others are invisible without a microscope. Regardless of their size, GI parasites can cause serious illness and even death in pets. Here, the most common GI parasites in pets:

Roundworms: Visible to the naked eye, roundworms resemble small pieces of spaghetti. In people, roundworms can lead to larva migrans, an illness caused by migration of young worms through the nervous system, liver, lungs, and other organs. They can even travel to the eye and cause blindness.

Hookworms: These worms attach to the intestinal wall and suck blood and other nutrients from their hosts, leading to severe blood loss and diarrhea in infected pets. And larvae found in the environment can penetrate the skin and cause illness in a new host. When humans are infected, the condition is called cutaneous larva migrans. The tell-tale symptom? Itchy skin lesions with a snakelike pattern.

Tapeworms: These are long, flat worms made up of numerous segments containing tapeworm eggs. For one species of tapeworm, the immature stage of the tapeworm lives inside of a flea. When your dog or cat grooms a flea off of its hair, it eats the flea—and the tapeworm, which then hatches inside your pet and continues its life cycle. You can become infected if you inadvertently eat tapeworm eggs or infected fleas.

Giardia: Giardia organisms are single-celled parasites that live in the intestines, and can be spread through fecal-contaminated water, food, or soil.

Whipworms: Whipworms live in the large intestines of dogs and shed eggs into the environment. When this occurs, the contamination can persist for years. Female whipworms can produce more than 2,000 eggs a day.

Coccidia: Coccidia are microscopic GI parasites. They can cause severe diarrhea in some infected pets.

How Parasites Can Make Your Pet Sick

Usually, GI parasites shed their eggs in the host’s feces. Once this occurs, other pets can be exposed through direct contact with the feces or contaminated soil, water, or plants. Some of these bugs can remain in the environment for months or years. Other parasites infect rodents and other small animals. When a dog or cat eats these animals, it becomes infected. Finally, some GI parasites can infect puppies and kittens when they nurse from their infected mothers, and puppies can sometimes become infected during fetal development.

How to Know If Your Pet Has Been Infected

Parasites are tricky, as often, dogs and cats don’t show any signs of illness. But if your pet has diarrhea, is vomiting or loses weight, he may have been infected. In this situation, a trip to your veterinarian is a good idea.

How Your Veterinarian Can Help

Fecal testing can detect GI parasites in most cases, but not always, which is why some veterinarians recommend deworming (administering medication to treat and control infections) even if the fecal test doesn’t confirm the existence of bugs. In fact, because puppies and kittens are commonly infected with GI parasites, many veterinarians routinely deworm them several times. Deworming medications are safe when used properly and come in a variety of formulations, including pills, chewable tablets, liquid medications and topical products that are applied to the skin between the shoulder blades. Your veterinarian can recommend the most appropriate deworming medications for your pet.

Available Treatment Options

There is no single medication that can treat and prevent all GI parasites, but many monthly heartworm preventive medications also control some of these microscopic bugs. Your veterinarian can recommend several safe and effective medications.

What You Can Do

To protect your pet and your family, take the following precautions:

  • Use a monthly heartworm preventive that also targets GI parasites. Pick up your dog’s feces promptly to reduce the risk of environmental contamination. Protect hands while cleaning up the feces and wash hands afterwards.
  • Clean your cat’s litterbox frequently to reduce the risk of reinfection, or, if you have other cats in the house, to prevent spreading the parasites. Also smart: Covering sandboxes when not in use to discourage cats from depositing feces there.
  • Encourage children to wash their hands after playing outside and before eating.
  • Schedule regular checkups with your veterinarian, and bring a stool sample from your pet for parasite testing.
  • Any new pet entering the home should be tested for GI parasites as soon as possible and treated if parasites are found.
  • If possible, prevent your pet from killing and eating rodents and other small animals.
  • Use effective flea control to reduce the risk of tapeworms. Thoroughly wash all fresh fruit and vegetables.
  • Do not allow your children to put dirt in or around their mouths.
  • Make sure your animals always have safe, clean drinking water.
  • Do not allow your pets to drink where other animals may have left feces such as water that is downstream from a farm.
This article was reviewed by a Veterinarian.