Giardia is a protozoan parasite that can infect the gastrointestinal tract of dogs and is capable of causing diarrhea, vomiting, weight loss and lethargy — although many infected animals show no signs at all. It is common throughout the United States and can cause infections at almost any time of year. Unlike many other infectious organisms, giardia persists longer in the environment when conditions are cool and moist.
Most dogs become infected by drinking water contaminated with feces. Giardia then infects the small intestine, and infected dogs pass microscopic cysts in their stool. These cysts can then infect another animal or person if ingested. Giardia cysts are very resistant in the environment, and can live for many months under the correct circumstances. These cysts are a threat to pet health, and giardia is a very common cause of pet diarrhea in the United States.
All dogs — even those on year-round parasite preventives and those without diarrhea — should have at least one to two fecal samples performed annually as part of their wellness exam to screen for gastrointestinal parasites, including giardia.
All dogs with symptoms of vomiting or diarrhea should be tested for giardia and other gastrointestinal parasites.
All newly adopted dogs should be tested for these parasites before they are introduced to a new home, and all dogs returning from high-risk environments (e.g., kennels, dog shows, boarding facilities, etc.) should be tested.
Testing for Giardia
There is no perfect test for giardia. Giardia is an elusive parasite, and cysts are shed only intermittently from the gastrointestinal tract of an infected dog. A single fecal sample has only a 70 percent chance of detecting an infection. Performing three fecal samples within five consecutive days increases the chance of detection to greater than 90 percent. There are other tests such as the giardia ELISA that can be used with a routine fecal sample to increase the likelihood of a diagnosis to about 95 percent.
If your dog is diagnosed with giardia, he will likely be prescribed medication, and your veterinarian will recommend a follow-up fecal sample two weeks after treatment.
A dog should be bathed on his last day of treatment to eliminate all giardia cysts from his hair coat. Wearing gloves, you should bathe and rinse his whole body as normal and then focus last on his hind end. Do not touch the rest of his body after you have bathed and rinsed around the anus. This will eliminate spreading any remaining giardia cysts around his hair coat. Pet bowls, toys, etc., should be disinfected in either boiling water or in a high-temperature dishwasher. Upholstery and carpeting should be steam-cleaned and allowed to dry. Hard surfaces can be disinfected with a dilute bleach solution (3/4 cup of bleach mixed with 1 gallon of water) or a disinfecting household cleaning product.
Troubleshooting: Dogs With Recurrent Giardia
Many dogs become reinfected with giardia as soon as treatment is finished because their environment remains contaminated. Following are tips for preventing giardia reinfection in your dog:
Allow your pet to defecate only on cement surfaces or surfaces that can be disinfected with aforementioned solutions or products. Dirt and grass areas can harbor large amounts of giardia for months. When treated dogs return to these environments, they can become reinfected and begin shedding giardia cysts within five to seven days.
Pick up all feces immediately and disinfect surfaces daily. If you walk your dog, carry a spray bottle of dilute bleach solution to easily disinfect surfaces.
Limit your dog’s exposure to high-risk environments where giardia could easily be spread, such as dog parks, kennels, dog day-care facilities, groomers, etc.
Test and possibly treat other dogs and cats in the household for giardia. Although dogs and cats are usually affected by different species of giardia, they can share infections, and cats can serve as a source of reinfection for household dogs.
Do not allow your dog to drink out of communal water bowls at pet stores or in public places.
Do not allow your dog to drink from puddles, lakes, ponds, rivers or streams, which may be contaminated with feces from other animals.
Do not allow your dog to eat his own feces or the feces or other animals.
Chronic Giardia Infection
It can be frustrating if a dog continues to test positive for giardia after treatment. The giardia ELISA test can remain positive for weeks to months following successful giardia treatment — so a positive test does not necessarily mean active infection. However, if giardia cysts are present in your dog’s fecal sample, active infection is present and you must redouble your efforts to limit your dog’s exposure to giardia and decontaminate your environment.
If additional treatments are unable to eliminate giardia infection in your dog, your vet may recommend a more extensive medical evaluation for your pet. Testing can also be performed to determine if the giardia infecting your dog is zoonotic — meaning an organism that can also sicken humans. The Centers for Disease Control (CDC) has detailed information available on giardia and how to prevent infection in people. The risk of infection is small because the type of giardia that affects humans is not usually the same one that affects dogs and cats, but it is good to be informed.