giardia in dogs and cats

giardia in dogs and cats
Posted by Dr. Kim Smyth on Sep 20 2011

With all the extra outdoor time our pets get during the spring, summer and fall months, I thought it would be a good idea to discuss a type of intestinal parasite often contracted outdoors: Gardia.

What is Giardia?

Giardia is unlike other intestinal parasites we’ve talked about before because it’s not a worm. Instead, it is an equally-unappealing protozoa, and it is infectious to both dogs and cats as well as humans.

Giardia is contracted by drinking contaminated water, either in the wild in streams or standing water, or in contaminated wells. There is some debate about its zoonotic potential (meaning whether or not it can spread from pets to humans), but if you are drinking from the same contaminated water source, you are at risk, too.

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It is tricky on many levels. First of all, it has two forms: a trophozite form - which lives in the intestine and causes diarrhea - and a cyst form - which allows it to live outside of a host so that it can be transmitted to the next poor dog or cat (or human). Once a cyst is swallowed, the cyst shell is digested away and the trophozite can then attach to the intestinal wall and do its work.


Giardia is tricky in another way--it is difficult to detect. It can cause on-and-off diarrhea in its host, and oftentimes it is mild enough that you may not notice it (especially if you let your pet out in the backyard to do her business "out of sight"). Giardia can also cause intermittent vomiting. While Giardia can be detected in a fecal sample at your veterinarian’s office, because it is shed only intermittently in the stool, chances are high that even if your dog or cat has Giardia, her fecal sample can still show up negative. Luckily, there is a test available that will show up “positive” or “negative” (kind of like a pregnancy test).

Thankfully, treating Giardia is relatively straightforward, as there are oral medications that do the job quickly. And because the cysts can get caught in your pet’s fur, it is recommended that she get a bath at least once during the treatment cycle.

Remember, there is some concern for transmission to humans, so be sure to wash your hands thoroughly after cleaning up after your pet.

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