Giardia: What You Need To Know

Giardiasis is a fairly common disease caused by a protozoan parasite that lives within the intestinal tract. There are effective medications for treating the disease, and pets rarely become seriously ill. Giardia usually affects dogs, particularly puppies, but can occur in cats and people too. 

What’s most important to know is that giardia is not usually transmitted directly from animals to humans without direct fecal to oral contact, but it is possible for animals and humans to come into contact with the same contaminated water source. Many dogs become infected from contaminated water sources such as pools, streams, lakes, or puddles.


Although sometimes a pet may have no outward symptoms at all, diarrhea (mild to severe) is the most common sign of giardiasis. The diarrhea is usually intermittent but can become chronic in nature, and the bowel movements are usually soft and mucousy. With chronic cases of giardiasis, malabsorption, weight loss, and lethargy can occur.


The infection is diagnosed with a fecal examination, but since giardia is shed intermittently, it is sometimes a difficult parasite to detect. For this reason, it is sometimes necessary to retest suspected patients in order to reveal an infestation.


Medications used to eliminate the parasite include Metronidazole, Furazolidone, and Fenbendazole. The choice of medication, dose, and length of treatment will depend on the severity of the infectation and the suspected resistance of the infection. Because giardia cysts can stick to the hair of the affected patient and be a source for re-infection, the affected pet should be bathed at least once weekly during the course of treatment.

Most pets do not become seriously ill from giardiasis, so the prognosis is almost always good. However, if a pet has any underlying disease(s), particularly one that compromises the immune system, giardiasis can have more serious implications.

As alluded to previously, not all pets that test positive for giardia have outward symptoms. However, given the prolific replication and resistant nature of the parasite, treatment is generally recommended for any pet testing positive with giardia cysts even if no outward symptoms are seen.

Environmental Decontamination

Over the last several years, giardia infestations have grown more and more resistant to standard treatments. Some patients may require medical treatment for 4-8 weeks or until the infestation is cleared.

For this reason, many steps are taken to control environmental contamination and limit the possibility for ongoing re-exposure/infestation. The most readily available disinfectant is bleach diluted 1:32 in water. Studies have shown this dilution to require less than one minute of contact time to effectively kill giardia cysts.

As for areas with lawn or plants, decontamination may not be possible without the risk of killing the foliage. If your pet has long hair, it may be necessary to shave the hair near the anus (“sanitary shave”), as well as the hair under the foot pads and between the toes.

If you have more than one pet, it may be best to keep pets separated. If that is not an option, keep all pets and the environment clean even if the bowel movements appear normal. To that end, be sure to pick up bowel movements from the environment as soon as possible. Go with your pet outside and encourage them to use an area that can be cleaned appropriately and make sure your pet does not eat the bowel movements.

Feel free to wash crates, beds, and bowls daily with a diluted bleach solution. When finished with medications, if the bowel movements appear normal, please wait 1-2 weeks prior to bringing in a fresh stool sample to be retested by the lab to ensure the infestation has been cleared. Wash your hands with soap and water after handling your pet or your pet’s bowel movements as humans, especially small children, can become infected by fecal to oral transmission.

If you have any further questions or concerns regarding giardia and/or your pet, please feel free to contact any of our three locations and we’d be happy to provide more information!

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