• Gastrointestinal (GI) parasites can cause serious illness in dogs; some parasites can also infect humans.
  • Your veterinarian can recommend medications to treat and control GI parasites.
  • Any new pet entering your home should be tested for parasites as soon as possible.

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. 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 in dogs and sometimes even death. Some parasites are even zoonotic, which means that humans can become infected. The most common GI parasites in dogs are:

  • Roundworms: Roundworms are visible with the naked eye and resemble small pieces of spaghetti. In humans, roundworms can cause 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 dogs. 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.
  • TapewormsTapeworms 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).
  • Whipworms: Whipworms live in the large intestines and shed eggs into the environment. Female whipworms can produce over 2,000 eggs daily, and environmental contamination can persist for years.
  • 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 dogs.

How Do Dogs Become Infected With Gastrointestinal Parasites?

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

Some parasites can infect small animals (like rodents), and dogs become infected when they prey on these small hosts and eat them. If a mother dog is infected, some GI parasites can infect puppies during fetal development or during nursing.

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

How Are Gastrointestinal Parasites Diagnosed?

Fecal testing can detect GI parasites in most cases. But even if testing doesn’t confirm parasites, your veterinarian may recommend treatment as a precaution; this is not harmful for your pet. Some parasites (like roundworms and tapeworms) can be seen in feces or vomit from an infected pet. Tapeworm segments sometimes cling to the hair around the anus.

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 no single medication can treat and prevent all GI parasites. Here are some tips for protecting your dog:

  • Use a monthly heartworm preventive that also targets GI parasites.
  • Pick up fecal material promptly to reduce the risk of environmental contamination.
  • Schedule regular checkups with your veterinarian, and bring a stool sample for parasite testing.
  • Encourage children to wash their hands after playing outside and before eating.
  • Have any new pet entering the home tested for GI parasites as soon as possible.
  • 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.