Giardiasis is caused by a parasite that takes hold in the intestinal tract and causes diarrhea, vomiting, weight loss, and tiredness. It’s passed to the environment through infected feces, and both dogs and cats can get it. If a pet has been infected with the giardiasis-causing organism, a vet can give him or her medicines to treat the problem, but it’s a stubborn bug and it may take more than one treatment to eliminate.


Giardiasis is a diarrheal disease that can affect many species: dogs, cats, and even humans. It’s caused by Giardia, a single-celled parasite that attacks the gastrointestinal tract of infected animals.

Among experts, there is some question about the number of Giardia subtypes that can cause disease in animals and the potential of these subtypes to also infect humans. Though humans are susceptible to infection with Giardia, infection by the same subtypes prevalent in animals is thought to be exceedingly rare but remains a point of controversy and investigation.

Giardia is found worldwide and in every region of the United States. According to the Companion Animal Parasite Council, approximately 16 percent of symptomatic dogs and approximately 10 percent of symptomatic cats have been found to be infected with Giardia.

The parasite lives in the intestines of infected animals and humans, and infected individuals pass the parasite in their feces, in the form of cysts, into the environment. These cysts can remain infective for months, especially when conditions are cool and humid. The infection is transmitted when a host ingests water from a contaminated pond, lake, or stream or ingests contaminated food or soil. Outbreaks of giardiasis are more common when animals are housed in crowded conditions, such as in kennels or shelters.

Symptoms and Identification

Clinical signs of giardiasis typically develop within five to 16 days after exposure to Giardia. In many cases, infected pets show no or slight signs of disease. Signs can include:

  • Weight loss
  • Appetite loss
  • Diarrhea (sometimes severe and with a very bad smell)
  • Flatulence
  • Vomiting
  • Lethargy (tiredness)
Because these signs can also be caused by many other diseases and health concerns, a complete physical examination and basic diagnostic testing of the stool and blood are recommended.

Several types of fecal tests can be used to diagnose giardiasis. In some cases, tests may need to be repeated more than once to obtain a definitive result.

In most cases, the disease course is mild. Some animals — particularly puppies, kittens, or animals with underlying health conditions — may have more severe diarrhea and vomiting and may require supportive therapy with fluids and anti-nausea medications. Dehydration can be a serious concern in these cases.

Affected Breeds

No breed predilection for giardiasis has been established in cats or dogs.


There are medications for treating giardiasis, but the infection can be difficult to cure, so multiple courses of treatment may be necessary. Pets should be bathed frequently throughout treatment to remove infective cysts from the coat.

Because pets that have been treated have no immunity against future infection, these pets can easily be reinfected. Therefore, living areas should be disinfected; ammonia, dilute bleach solution, or steam cleaning can be effective.

If there are other pets in the household, medications may be administered to them as a preventive measure — and because identifying the infection can be frustrating it’s reasonable to assume other pets in the household have been exposed to the same Giardia sources and are likely to be infected. Contaminated soil can remain infective for months under certain conditions, so walking treated dogs in a different area may reduce the risk of reinfection.


Giardia is common in the environment. Outdoor dogs and cats, working or hunting dogs, and pets that swim or have contact with potentially fecal-contaminated water can be at risk for exposure.

Preventive measures should include regular removal of feces from the yard or kennel. As much as possible (or reasonable, given the need for exercise and general quality of life), prevent pets from drinking from, or swimming in, lakes, streams, and ponds.

Most veterinarians recommend testing new puppies or kittens or adult pets for Giardia before they are introduced to your other pets.

Though it is considered controversial whether humans and pets can be infected by the same subtypes of Giardia, it is always a good idea for people to wash their hands after playing with pets or disposing of fecal material (infective or not).

This article has been reviewed by a Veterinarian.