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Friday, June 21, 2024


In the past I have discussed why we ask for fecal samples on a regular basis. Here I will elaborate on one of the most common intestinal parasites in our city: giardia. This bug is microscopic and ubiquitous in our environs.

Giardia is a one-celled parasite and is not considered a worm in the traditional sense. It is present in contaminated water, including ponds, puddles and streams. It is transmitted when a dog drinks water with a cyst stage of the organism. These cysts are hardy and can survive in the environment for months. Once ingested the cyst transforms into a trophozoite, which can swim within the intestines. This form also is capable of reproducing. When in sufficient numbers, the trophozoites can damage the intestinal wall, leading to blood in the stool and intestinal discomfort.

It takes from five to twelve days from ingestion of cysts to passage of new cysts in the feces. Dogs do not have to eat stool or even drink contaminated water to become infected (although water is the most common source of the organism), they can inhale them off of the ground, or lick them off fur.

Giardia causes foul-smelling stool, which can range from soft to watery, frequently with a green hue present. On occasion, blood can be seen. Dogs may also vomit in some cases. Should the infection be present for a long time, weight loss can ensue. The diarrhea may be intermittent as well. Many dogs with giardia may also be normal, without clinical signs.

We diagnose giardia through fecal examinations. In healthy dogs without clinical signs, we generally check a routine fecal float, which also specifically looks for other parasites as well. If we suspect giardia, we may submit a more specialized fecal test, which looks for chemical markers of the organism. In some cases, we may elect to treat for giardia even if the stool sample is negative. Why? Because giardia cysts are not always shed in the stool. Think of them like chickens – they don’t lay an egg every day!

Puppies are more prone to giardia as their immune systems are not fully developed. This is part of the reason we check stool samples on them several times. Adults that come from the country or are in shelters /boarding facilities may be more prone to infection as well.

Treatment is based upon clinical signs – we treat the diarrhea – and we add one or two medications to help eliminate the organism. Giardia has proven to not be readily eliminated in some dogs, so repeated fecal testing to see if we have resolved the infection is common. On occasion, we have to retreat for the bug. Post treatment a recheck fecal sample is usually requested, within two to four weeks.

Giardia is an organism that can affect people, too. In general people contract guardian in a similar way as dogs: from contaminated water. Rarely is it transmitted from dogs to humans. If your pup has giardia, treat as indicated by your veterinarian and maintain good personal hygiene. Wash your hands well!


Dan Teich, DVM is the Medical Director of District Veterinary Hospital, 240 7th Street, SE.

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