• Giardia is a parasite that is found worldwide and in every region of the United States.
  • Giardiasis (the disease that Giardia causes) can cause diarrhea, appetite loss, and vomiting.
  • Giardiasis is transmitted to dogs and catsthrough contact with infected feces or with water, food, or soil that has been contaminated by infected feces.
  • Pets can often be infected with Giardia without showing outward signs.
  • The risk of infection can be reduced by avoiding high-risk environments and behaviors.

What Is Giardiasis?

Giardiasis is a diarrheal disease that can affect many species, including dogs, cats, and humans. It is caused by Giardia, a single-celled parasite that attacks the gastrointestinal tract of infected animals. Among experts, there is some question about (1) the number of Giardia subtypes that can cause disease in animals and (2) the potential of these subtypes to also infect humans. While 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% of symptomatic dogs and approximately 10% of symptomatic catshave 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/moist. 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 a kennel or shelter.

Signs of Giardiasis

Clinical signs of giardiasis typically develop within 5 to 16 days after exposure to Giardia. In many cases, infected pets show no or slight signs of disease. Signs can include:

  • Weight loss
  • Inappetence (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 problems, a complete physical examination and diagnostic testing may be recommended.

Diagnosis and Treatment

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 such cases.

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 throughout treatment to remove infective cysts from the haircoat. 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. Contaminated soil can remain infective for months under certain conditions, so walking treated dogs in a different area may reduce the risk of re-infection.


Giardia is common in the environment. Outdoor dogs and cats,working or hunting dogs, and petsthat swim or have contact with potentially 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, prevent pets from drinking from, or swimming in, lakes, streams, and ponds.

Your veterinarian may recommend testing new puppies or kittens or adult pets for Giardia before they are introduced to your other pets.

While it is considered controversial whether humans and pets can be infected by the same subtypes of Giardia, it is always a good idea to wash your hands after playing with your pet or disposing of fecal material.