Giardia is an intestinal protozoan parasite common in mammals — including pet dogs and cats. My clinic sees giardia in 5 to 15 percent of pets.
The good news is giardia in pets is very unlikely to spread to humans. There are currently eight strains of giardia, labeled A through H. Dogs usually are infected with C and D and cats with F. Humans, fortunately, do not get these types. If we pick up giardia, it is A and B, which are very rare in dogs and cats.
This parasite is known to be found in stagnant water but also can be present in contaminated food and soil. Infection requires ingestion of the trophozoite or cyst form of the parasite. Once ingested, it can cause inflammation of the intestinal tract, exhibiting as diarrhea and sometimes vomiting. Some animals can carry the parasite without being affected. Giardia can be shed in the stool about 5 to 14 days after infection, and it affects animals more if they have a weaker immune system or other illness. If an animal becomes infected, giardia may cause poor intestinal absorption of vitamins and nutrients.
Giardia is actually commonly found in young puppies and kittens. It is possible their mothers have the parasite and are not affected, then pass it on to their young. If any dog or cat has diarrhea, I always check a stool sample to see if the parasite exists to treat for this properly. Most commonly, a fecal centrifugation test is done to look for the parasite visually, but there are also chemical tests looking for parts of the parasite. This parasite can also have intermittent shedding in the stool, so it may take more than one fecal test to find it.
We often treat young patients with fenbendazole (Panacur) medication, but other medications may also be needed, including metronidazole or febantel. Some pets benefit from a bland diet for several days and the use of probiotics. Bathing our pets, if possible, can also help wash any fecal matter off their bodies – especially around the hind end and feet. After treatment, we check the stool again to make sure the infection is gone. We have to be careful, however, about the interpretation of results. A chemical PCR or antigen test can remain positive for months following actual clearance of the parasite. As we well know, a PCR test only helps confirm a diagnosis and is not meant as a complete diagnostic tool. We have to go not only by the test results but also determine if the patient is showing symptoms.
Giardia cysts can last a long time in the environment in Southern California since we typically don’t have freezing temperatures. They can also be killed by direct sunlight. Quaternary ammonia cleaners also kill the parasite but may be impractical to use on certain areas, including lawns. A properly chlorinated pool should not be able to be contaminated.
Any pet with this parasite must have its stools cleaned up well and promptly to avoid continued exposure and re-infection. Most pets will eventually also develop their own local immune defense along the walls of the intestines but may later show signs of re-infection if their immune system wanes. In some cases, treatment and elimination can be very frustrating.
If your pet shows any diarrhea, it is always best to consult your veterinarian. Make sure, if possible, to bring in a stool sample to include with the examination to determine the cause and best treatment better. We want you and your pets to be safe and healthy.
Dr. Ron Resnick has been in practice for more than 32 years and previously operated two veterinary hospitals. He taught at Harvard University and graduated from Tufts University, considered the best veterinary school in the world. He operates an animal hospital in Simi Valley.
