Q: In the past, we’ve had pet dogs and cats that came down with giardia, but they usually had symptoms. More recently, we’ve had both an older dog and a puppy test positive for symptom-free giardia. We’re a little confused. Can you clarify this for us?

A: OK, fair warning: Don’t read this one over breakfast! But do read the answer here, because we’re going to explain the common and often-misunderstood microscopic digestive parasite known as Giardia intestinalis that can affect dogs and cats -- and humans, too (especially young children or anyone with compromised immunity). Giardia’s usual symptoms may include gas, abdominal discomfort and vomiting, although diarrhea is the most common telltale.

But diarrhea can come and go, and can have a variety of causes, so giardia may remain undiagnosed because pet owners assume their dog or cat just “got into something” it shouldn’t have eaten. Because recurrent diarrhea can take a toll on a pet’s health, we’d much prefer to pinpoint a cause and apply effective treatment. (This is one of the reasons we urge our clients to have a fecal test performed every six months even if their pets seem perfectly healthy. But especially contact your veterinarian if a pet’s diarrhea persists for more than a day or two, or recurs after it seemed to clear up on its own.) 

Then again, as in the questioner’s experience, it’s possible to have asymptomatic giardia. In fact, that’s the case more often than not. So you may wonder, “If my dog has giardia but isn’t sick, then why bother getting it diagnosed and treated?” Because every time your dog poops, he’s potentially shedding giardia cysts that contaminate the surrounding environment, including lawns, soil and water sources, enabling the parasite to be transmitted to other pets, and possibly to human family members -- any of whom may actually get sick. Probably the most likely transfer medium is contaminated water -- ranging from a rain-puddle on a sidewalk to a pond, stream or lake. So all your dog or outdoor cat has to do to ingest giardia is lick up some of that water.


Submit a Letter to the Editor for the Laurel Leader, Columbia Flier and Howard County Times

Giardia is diagnosed by a fecal lab test. Animal hospitals can do in-office testing, which is unfortunately only about 70 percent accurate. When we suspect giardia, we prefer to send fecal samples out to labs equipped to perform something called an enzyme-linked immunosorbent assay (ELISA) test. This is a much more sensitive test delivering more accurate results. The ELISA test can actually reveal both past and present exposure to giardia, but if it doesn’t indicate the presence of an active infection complete with cysts and the pet has no symptoms, we may opt for no treatment.

When cysts are present, however, that means there’s an active infection, and there are a few effective oral-medication treatment options. Once the course of anti-protozoal medication is complete, we re-test a stool sample. In some cases, treatment may need to be repeated, and there’s some concern among veterinarians that giardia is becoming resistant to the medications now available. This can result in animals becoming persistent carriers even if they’re not showing symptoms.

If your pet is diagnosed with giardia and treated by your veterinarian, there are some additional steps you can take at home to reduce the chances of that pet becoming reinfected or spreading the infection to other dogs or cats in the home, or to susceptible humans. Wash your hands thoroughly after touching your pet or being licked by him. Promptly and carefully pick up after him on walks and in the yard, and wash your hands immediately after. Wash all pet bedding in hot water, and dry in a dryer at the highest setting (this is one advantage of having machine-washable pet bedding). Following and during the course of medication, also thoroughly bathe your pet’s rear end with pet shampoo or Johnson’s baby shampoo to wash off any cysts that may be caught in her fur back there.

To find out more about giardia prevention and treatment, contact your veterinarian. And you can read more detailed info at the Centers for Disease Control and Prevention website: cdc.gov/parasites/giardia/giardia-and-pets.html.