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When your pet has been diagnosed with Giardia, it usually creates a lot of questions for pet owners. How did my pet get this? Can my family become infected? Do we need to treat, and if so, how? What is Giardia?

First, we will start with what Giardia is. Giardia are single celled organisms that you cannot see in the stool. They can be picked up from infected water sources, infected stool or soil, or  infectious Giardia cysts that can become attached to a pet’s fur near the tail or rectum when an infected animal passes stool. Giardia has 2 forms: the trophozoite and the cyst. The trophozoite is the parasitic stage that attaches to the intestines of the infected animal. The cysts are the contagious stage that have a hard shell and can live in the environment potentially for months.

Giardia is diagnosed through testing of a fecal sample. In the past, the fecal was checked under the microscope for the presence of Giardia cysts. Since these cysts are only shed intermittently , this was not always a reliable way to diagnose or rule out Giardia. More recently, Giardia Elisa testing has dramatically improved the ability to detect Giardia. After infection, it takes 5 to 12 days in dogs or 5 to 16 days in cats for Giardia to be detected in the stool.

Humans can become infected but it is very rare and they are typically infected only by a specific subcategories of Giardia. It is recommended to maintain good hygiene like hand washing and safely removing feces from the yard as a precaution. Common fecal testing methods do not indicate which subcategory of Giardia is detected so common sense hygiene is best practice.

Giardia can cause diarrhea in some pets, but sometimes causes no symptoms. We do not know why Giardia causes diarrhea in some pets but not others. If no symptoms are present it is not always considered necessary to treat, as a healthy immune system can often clear Giardia on it’s own in a few weeks. If your pet comes in contact with other pets (boarding, training classes, dog parks or lives with other pets) it may be beneficial to treat to avoid transmission.

Treatment generally consists of using a broad spectrum de-wormer called fenbendazole along with an antibiotic called metronidazole.  Both are typically given for 5 days. Because giardia cysts can become stuck to the hair around the rectum area (and can be contagious) a bath at the beginning and end of treatment is advised. For the 3 days in between baths, cleaning the anal/tail area with unscented baby wipes is recommended. Removing feces from the environment as quickly as possible will help prevent other animals from coming in contact with the infectious cysts or reinfection of the pet being treated. A fecal should be rechecked 7 days or more after treatment has been finished. Because Giardia can sometimes be difficult to eradicate (or because reinfection has occurred) a 2nd round of treatment for a longer period of time may be needed.

Giardia can be killed on surfaces with common disinfectants. Freezing temperatures and direct sunlight can kill Giardia in the environment. Lawns and plants however cannot be decontaminated without killing the plants or grass so getting into the habit of picking up stools as soon as possible lessens the chance of infectious cysts. There is no vaccine available for the prevention of Giardia.

The best way to protect your pet from Giardia (and other intestinal parasites) is through routine fecal testing (one or twice per year) and disposing of stools promptly.