GIARDIA

Giardia duodenalis is a protozoan parasite (think swimming single cell critter with multiple tails) that can infect and cause intestinal disease in dogs, cats, humans and many other mammalian hosts.  (Other Giardia species can infect birds and reptiles as well.)  It is, in fact, the most common intestinal parasite of humans worldwide.  In a recent national study, 19% of dogs and 11% of cats with diarrhea tested positive for Giardia.

Infection occurs when Giardia cysts from fecal-contaminated areas or water are ingested (why hikers should not drink untreated water from streams).  These cysts can survive for months in cold water and cool, moist conditions.  The cysts break open in the small intestine where the organism attaches to the intestinal wall to feed.  This causes varying amounts of inflammation and decreased digestive function.  While many infected animals remain asymptomatic, some develop diarrhea and occasionally vomiting.  All infected animals will shed Giardia cysts.  Young animals are more likely to be both infected and sicker than are older animals.  This is because of their immature immune system and greater susceptibility to the weakening effects of stress and other illnesses. A full two thirds of all the puppies with diarrhea at MVC tested positive for Giardia. 

Our reference lab tests for Giardia with a stool centrifugation technique that looks for the actual protozoal organisms,the same test used to look for other intestinal parasites. We recommend fecal testing all young animals that have been in a pet store/kennel/cattery situation as well as any animal with diarrhea.  All animals testing positive should be treated to help prevent contamination of the surroundings.  Some animals have Giardia infections that are harder to eliminate than others so we will sometimes treat animals with two medications simultaneously.  Repeat treatment may be necessary if symptoms do not completely resolve or if they return.

Though not likely, the possibility of Giardia transmission from pet to human family members theoretically exists.  Decontamination of the environment is sometimes recommended but is often not practical.  Practicing good hygiene around pets (especially important for children and immunocompromised adults) and regularly removing stool from the home area as promptly as possible are the best approaches to prevent problems.  For pets with Giardia and diarrhea, cleaning their rear end with shampoo has been reported to decrease environmental contamination as well as re-infection.