Deworming and Prevention of Gastrointestinal Parasites in Dogs and Cats

  • Gastrointestinal parasites can cause serious illness in pets, and some parasites can infect humans.
  • Deworming involves administering medication to treat and control gastrointestinal parasites. Your veterinarian can recommend the most appropriate deworming medications for your pet.
  • Any new pet entering your home should be tested for parasites as soon as possible and treated if parasites are found.

What Are Gastrointestinal Parasites?

Gastrointestinal (GI) parasites include any parasites that live in the stomach or intestines of a host. A variety of GI parasites affect dogs and cats. They range from roundworms and tapeworms, which are visible with the naked eye, to microscopic organisms like coccidia and Giardia. Regardless of their size, GI parasites can cause serious illness and sometimes even death in pets. Some parasites are  zoonotic, which means humans can become infected. The following are the most common GI parasites in pets:

  • Roundworms: Roundworms are visible with the naked eye and resemble small pieces of spaghetti. In humans, roundworms can lead to larva migrans, an illness caused by migration of young worms through body organs such as the liver, lungs, and nervous system. Young roundworms may also travel to the eye, where they can cause blindness.
  • Hookworms: These worms attach to the intestinal wall and suck blood and other nutrients from their hosts. Hookworms can cause severe blood loss and diarrhea in infected pets. Infective hookworm larvae in the environment can penetrate the skin and infect a new host. When this happens in humans, the condition is called cutaneous larva migrans. People with this condition may experience itchy skin lesions with a snakelike pattern.
  • Tapeworms: Tapeworms are long, flat worms that are actually made up of numerous segments; each segment contains tapeworm eggs. Humans can become infected if they inadvertently eat tapeworm eggs or infected fleas (which can contain tapeworm eggs).
  • Giardia: Giardia organisms are single-celled parasites that live in the intestines. Fecal-contaminated water, food, or soil can be sources of infection.
  • Coccidia: Coccidia are microscopic GI parasites. They can cause severe diarrhea in some infected pets.
  • Whipworms: Whipworms live in the large intestines of dogs and shed eggs into the environment. Female whipworms can produce over 2000 eggs daily, and environmental contamination can persist for years.

How Do Pets Become Infected With Gastrointestinal Parasites?

In most cases, eggs or infective stages of GI parasites are shed in the host’s fecal material. Once parasites are in the environment, other pets can be exposed through direct contact with feces or exposure to soil, water, or plants that have been contaminated with feces. Some GI parasites can remain in the environment for months to years.

Some parasites can infect small animals (like rodents); pets become infected when they prey on these small hosts and eat them. Some GI parasites can infect puppies and kittens when they nurse from their infected mothers, and puppies can sometimes become infected during fetal development.  

Tapeworms are slightly different in that they can be transmitted by fleas. The immature stage of the tapeworm lives inside the flea. When a pet grooms a flea off of its hair, it eats the flea (and the tapeworm). The tapeworm then hatches inside the pet and continues its life cycle.

What Are the Clinical Signs of Gastrointestinal Parasites?

Diarrhea, vomiting, and weight loss can be among the clinical signs of GI parasite infection. However, many infected pets don’t show any clinical signs at all. The best way to tell if your pet is infected is to have him or her tested for parasites. 

What Is Deworming?

Deworming involves administering (or in some cases, applying) medication to treat and control infections with GI parasites. Because puppies and kittens are commonly infected with GI parasites, many veterinarians routinely deworm these young patients several times. Fecal testing can detect GI parasites in most cases, but parasites are not detectable all the time. Even if testing does not confirm parasites, your veterinarian may recommend deworming as a precaution. This is not harmful to your pet. 

Deworming medications come in a variety of formulations, including pills, chewable tablets, topical spot-on products that are applied to the skin between the shoulder blades, and liquid medications given by mouth. Your veterinarian can recommend the most appropriate deworming medications for your pet.

How Can I Treat and Prevent Gastrointestinal Parasites?

Your veterinarian can recommend several safe and effective medications to treat GI parasites. Fortunately, many monthly heartworm preventive medications also control some of these parasites, but there is no single medication that can treat and prevent all GI parasites. Here are some tips for protecting your pets:

  • Use a monthly heartworm preventive that also targets GI parasites.
  • For dogs, pick up fecal material promptly to reduce the risk of environmental contamination.
  • For cats, clean the litterbox frequently to reduce the risk of spread in a multicat household or reinfection in a single-cat household. Also, cover 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 exposure to tapeworms.