Giardia is a one-celled parasite found not only in the small intestine of dogs and cats, but also in most wild animals worldwide as well as many people in third-world countries.
There’s much we don’t know about the giardia parasite. For example, we don’t know exactly how many species there are, or which ones affect which animals. We also don’t know everything about the life cycle of the various species we’ve identified.
It’s thought that while exposure to giardia is common, acquiring disease from the parasite is less common. Giardia is ubiquitous in the environment, meaning it’s pretty much everywhere, including rivers, ponds, puddles and lots of other places.
Giardia is a zoonotic disease, which means if your dog or cat has it or a human family member has it, the rest of the family — humans and animals — can be infected. Puppy mills and other facilities that house lots of dogs are breeding grounds for the spread of the parasite.
How Giardia Is Transmitted
Your pet can acquire giardia by ingesting infected cysts contained in the poop of another animal. Contamination can occur directly or indirectly through contact with infected cysts. If a dog is giardia positive and licks his backside and then licks other dogs, cats, or humans, there is potential for transmission to occur. The most common route of transmission is through feces-contaminated water.
Once inside a dog or cat’s small intestine, the cyst opens and releases the active form of the parasite. These forms move around and attach themselves to the walls of the intestine where they reproduce by dividing in two.
Eventually, the active forms of giardia encyst (build cysts around themselves) and are passed from the animal’s body in feces. The poop then contaminates water sources, grass, soil, and other surfaces. Giardia thrives in cool, moist environments.
Symptoms of Giardiasis
Most giardia infections are asymptomatic, meaning there are no obvious signs your pet is carrying the parasite. When symptoms are present, the most common is diarrhea, which can be acute (sudden), chronic or intermittent.
Many people don’t consult their veterinarian about their pet’s soft, mushy stool because often it improves on its own after several days. About the time you’re ready to call your vet for an appointment, the stool firms up and all seems fine again. Stools can be normal for a week or two, and then the soft stool starts again.
Because of the on-again off-again nature of loose stools associated with giardia, many pet owners assume the dog got into something he shouldn’t have or had a meal that didn’t agree with him. That’s why so many cases of giardia go undiagnosed.
After a week, month, or sometimes years of an undiagnosed giardia infection, a giardia positive animal can experience an acute and very debilitating bout of bloody, dehydrating diarrhea. Most pets with giardia don’t lose their appetite, but in chronic cases they can lose a lot of body weight. They’re still eating, but they’re getting thinner.
This is because a giardia infection interferes with the digestion and absorption of nutrients from the diet. It can also damage the lining of the intestine. In fact, this parasite is at the root of many cases of chronic gastrointestinal (GI) inflammation in dogs and cats.
I would go so far as to say that many cases of inflammatory bowel disease (IBD) or dysbiosis (leaky gut syndrome) could be caused by an undiagnosed giardia infection. Many of these patients have a history of being giardia positive as puppies or kittens, and they go on to develop IBD as adults.
I also see a number of pets with chronic diarrhea, malabsorption and other digestive issues who end up being giardia positive. It’s something many primary care veterinarians don’t routinely check for.
The giardia parasite is microscopic and can’t be seen with the naked eye, so you can’t assume because you don’t see anything weird in your pet’s poop that there’s nothing there. And unfortunately, parasite testing performed at your veterinarian’s office instead of an independent laboratory may not be accurate.
Estimates are that up to 30% of in-house tests return a false negative, which means there are a lot of giardia-positive animals testing negative for the infection. If you think your pet may have giardia, I recommend you ask your veterinarian to send a stool sample to a commercial laboratory for analysis.
I also recommend an ELISA or PCR test for giardia for any pet with a history of GI issues. A fecal ELISA or PCR test is preferable to the standard fecal flotation test because it checks for the presence of giardia antigens. A standard fecal float only detects giardia cysts, which may or may not be shed in the stool sample being tested. This is another reason veterinarians often fail to diagnose the parasite early on.
Labs now offer a diarrhea panel that checks for other common causes of diarrhea. The panel is a good diagnostic choice for any dog or cat with intermittent GI issues.
If your pet has been diagnosed with giardia, your veterinarian will prescribe medication to eliminate the parasite. Unfortunately, the giardia parasite is becoming resistant to many antiprotozoal drugs, which means more and more pets are becoming persistent carriers of the infection. This means that even after treatment with medication and repeated stool samples, your dog or cat might still be positive.
As I mentioned, the antigen test is what we use to diagnose the parasite. It can be positive for up to 6 months after treatment because it takes quite a while for your dog or cat’s body to clear the antigens out of the bloodstream after the parasites have died.
Immediately following treatment for giardia, I recommend veterinarians run a fecal float test once a month for 3 to 4 months to ensure it is negative, followed by an antigen test to ensure the infection has been fully resolved.
The reason for repeated fecal floats post-treatment is, again, because cysts aren’t typically passed in every stool sample. You may get one or two fecal samples that are negative, but if your pet is persistently infected or if the treatment didn’t work, he could still be positive. I believe it’s important to do repeated testing after treatment to be absolutely sure the infection has been cleared.
I’ve tried many natural protocols to eliminate giardia without the use of drugs, and I’ve had some success using combinations of antiparasite herbs such as berberine (Oregon grape root), ginger, cinnamon, black walnut, olive leaf, cat’s claw, and Pau d’arco. I’ve found these substances do a good job reducing the parasitic load in dogs and cats, but they don’t always resolve the infection.
If you choose to treat your pet all naturally, I recommend that you extend your intermittent stool checks to 9 months because I most commonly see a recurrence of cysts between the 6 and 9-month mark after an all-natural giardia treatment protocol.
Once your pet has been fully cleared of the parasite, I strongly recommend partnering with a functional medicine veterinarian who can provide an intestinal recuperation plan. There are many articles and videos here on the Healthy Pets site about leaky gut and inflammatory GI disorders you can refer to as well.
An intestinal recuperation plan will help your giardia positive pet avoid long-term consequences from the damaging effects of the parasite.
Preventing a giardia infection involves being aware of several predisposing factors, including avoiding kenneling your pet with other animals of unknown parasitic status, picking up your dog’s poop outside, and avoiding walking your dog in areas where other animals have pooped. As much as possible, also prevent your pet from drinking water from outdoor sources.
I also recommend asking your veterinarian to test a fecal sample from your pet using an outside lab twice a year. This will help identify and treat parasitic infections before they have a chance to cause a lot of GI inflammation.
On a side note, I don’t recommend routine deworming of dogs. There isn’t a universal dewormer that kills every parasite imaginable. You can’t give your pet a pill that will take care of, for example, giardia, coccidia and tapeworm. Don’t just assume your pet has parasites and offer unnecessary medications. No drug is entirely safe, and there is always a certain amount of risk involved in giving medications, so please only do so when necessary and not “just in case.”
I also don’t recommend routine use of natural dewormers “just in case.” I’ve seen many cases of significant GI inflammation caused by unnecessary doses of strong herbal preparations that were totally unnecessary because the animal had no parasitic infection.
It’s almost never a good idea to give your pet a drug or even a natural remedy just-in-case. The just-in-case preventive I absolutely recommend is to proactively test your dog’s or cat’s feces on a regular basis to be sure your pet is negative for parasites.