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Close up of a giardia organism

(This article will often discuss giardia in dogs; while felines can get giardia, it is diagnosed more often in canines).

What is Giardia?

Giardiasis is an intestinal infection in humans and animals.  Giardia is a simple one-celled parasitic species; it is not a "worm", bacteria or virus. There are seven genotypes.

"... the majority of dogs infected with Giardia do not have diarrhea, vomiting, or any other signs of illness."

Giardiasis can be an important cause of illness, especially diarrhea, in animals and people. However, the majority of dogs infected with Giardia do not have diarrhea, vomiting, or any other signs of illness.

The Giardia organism has two forms. A fragile feeding form, known as the trophozoite, exists in the gut of infected animals, while a hardy cystic form is shed in feces and can survive several months in the environment, particularly in water and damp environments.

How do dogs get giardia?

white dog drinking from puddle

A dog becomes infected with Giardia when it swallows the cyst stage of the parasite. Once the cyst passes into the dog's intestines, it goes through a transformation to the trophozoite, or feeding form, and attaches to the intestinal wall to feed.

Trophozoites reproduce by dividing, and some transform into the cystic form. Eventually, the dog passes infectious cysts in its stool. The time it takes from ingestion of cysts to passage in feces is 5 to 12 days in dogs and 5 to 16 days in cats.

"Giardiasis can be transmitted by eating or sniffing the cysts from contaminated ground, or by drinking contaminated water."

These cysts are immediately able to infect another animal. Giardiasis can be transmitted by eating or sniffing the cysts from contaminated ground, or by drinking contaminated water.

What are the clinical signs of giardiasis?

These microscopic parasites attach themselves to the intestinal wall and the damage causes an acute, sudden-onset of foul- smelling diarrhea. Giardia infection in dogs may lead to weight loss, chronic intermittent diarrhea, and fatty stool. The stool may range from soft to watery, often has a greenish tinge to it, and occasionally contains blood. Infected dogs tend to have excess mucus in the feces. Vomiting may occur in some cases.

"Giardia is not usually life threatening unless the dog’s immune system is immature or immunocompromised."

Diarrhea may be intermittent. Most dogs do not have a fever but may be less active. Giardia is not usually life- threatening unless the dog’s immune system is immature or immunocompromised. Many dogs will be asymptomatic carriers, never developing any signs of illness.

tube for fecal kit

How is giardiasis diagnosed?

The easiest way to diagnose giardia is by running an intestinal parasite screen--results are usually available in 24 hours.  We will request a fresh stool sample for this test.  The fresher the sample, the more accurate the results.  If you are not able to bring a sample in quickly, please refrigerate it.  We only need about a teaspoon amount and can provide you with a fecal kit to make this process easier.  However, you are welcome to bring the sample in a bag or clean plastic bowl (with lid).

How is giardiasis treated?

The most common drugs used to kill Giardia are fenbendazole (Panacur) and metronidazole. These drugs are normally given for three to ten days to treat giardiasis. Both drugs may be given in combination if necessary. This combination is usually administered to dogs with refractory diarrhea (diarrhea that hasn't responded to treatment). Supportive treatment with other drugs may be needed as supplemental therapy if dehydration or severe diarrhea is present. All infected pets should be re-tested two to four weeks after completion of treatment. Your veterinarian will help determine what course of treatment is best for your pet.

Can my dog give me or my family giardia?

Giardia can cause diarrhea in humans and can potentially be passed from dogs to humans. In the past, it was assumed that cats and dogs, along with wildlife, were an important source of infection for humans. Genotype A can infect humans, dogs, and cats while B can infect both humans and dogs.

"...contaminated municipal water supplies are responsible for many outbreaks.”

However, human-to-human transmission is also important and contaminated municipal water supplies are responsible for many outbreaks.

If your dog is diagnosed with giardiasis, environmental disinfection and good personal hygiene are important to prevent accidental spread to humans. In particular, people with immunodeficiency, such as AIDS or cancer, or who are undergoing chemotherapy, should use extreme care, especially when handling feces or after administering medications.


For environmental disinfection, you can use chlorine bleach at 1:32 or 1:16 dilutions, or 1-2 cups in a gallon of water (60-120 ml/L). However, be sure that the affected surfaces can be safely treated with bleach. Lysol® and quaternary ammonium compounds (Parvosol®, etc.) are also reported to be effective in killing the cysts. Giardia cysts are susceptible to drying so try to keep your environment as dry as possible. For best results, thoroughly clean the pet's living and sleeping areas and then allow the areas to dry out for several days before reintroducing pets.

This client information sheet is based on material written by: Ernest Ward, DVM. Updated by Robin Downing, DVM, DAAPM, DACVSMR, CVPP; Amy Panning, DVM

© Copyright 2017 LifeLearn Inc. Used and/or modified with permission under license.

We have modified it to fit Lien Animal Clinic's views and guidelines. 2018