Giardia and Chronic GI Issues

by Dr. Becker

Your veterinarian may have just told you that your pet has giardia. And the news may have come as a complete surprise since you had no idea there was anything wrong with your dog (or less often, your cat). That’s because the majority of pets with giardia show no obvious signs of infection. For those pets who do experience symptoms, the most common is diarrhea that can be acute, chronic, or on-and-off.

What happens with a lot of dog owners is, about the time they’re ready to call the vet about their pet’s loose stools, the situation seems to correct itself. Diarrhea caused by a giardia infection can come and go, which causes many pet parents to write off the occasional loose stool as the result of indiscriminate eating or a random food sensitivity.

This is exactly why so many cases of giardia go undiagnosed – sometimes for months or even years.

Eventually, a dog with a long-standing giardia infection can suffer a severe, debilitating episode of bloody diarrhea that causes dehydration. Most of these pets don’t lose their appetite, but they often do lose a noticeable amount of weight. This is because the parasitic infection in the GI tract is interfering with digestion and absorption of nutrients from the food they eat.

Giardia Is Often the Root Cause of Chronic GI Issues

In my experience, the giardia parasite is the root cause of many cases of chronic GI inflammation in dogs and cats. I see a lot of patients in my practice who are referred for inflammatory bowel disease (IBD) who were also giardia-positive as puppies or kittens. I also see many referrals for chronic GI issues like persistent diarrhea or malabsorption who test positive for giardia.

Many people aren’t aware that giardia is abundant in the environment. It’s in puddles, ponds, rivers and other cool, moist environments.

Scientists don’t know a lot about this one-celled organism. We do know it is frequently found in dogs and cats, most wild animals, and even in many people living in third world countries. Puppies bred in puppy mills and dogs living in cramped quarters with lots of other dogs also often carry the giardia parasite.

While exposure to giardia is common, acquiring disease from the parasite is less common. The disease is zoonotic, however, which means it can be transmitted from animals to humans and vice versa.

How Your Pet Gets Infected

Your dog can be exposed to giardia by ingesting an infected cyst lurking in another animal’s feces. Contamination occurs either directly or indirectly through contact with infected cysts, and the most frequent point of transmission is when a dog is exposed to contaminated water.

Once a giardia cyst makes its way to your dog’s small intestine, it opens to release the active form of the parasite. These organisms have the ability to move around and attach to the walls of the intestine, where they reproduce.

Eventually, the active forms of the parasite encase themselves in cysts and pass from the dog’s body in feces. The infected poop then contaminates water sources, grass, soil and other surfaces.

Another way transmission can occur is if a dog with giardia licks his behind and then licks another pet or a human.

Diagnosing Giardia

In case you think you can learn if your pet is infected by looking at his poop, don’t bother. The giardia parasite is microscopic and can’t be seen with the naked eye.

There are a few things you should know about giardia testing. One is that parasite testing done in-house (at your vet’s office) rather than at an independent laboratory is not nearly as accurate. Estimates are that up to 30 percent of in-house tests return a false negative. This means there are a lot of pets walking around with giardia who tested negative for the infection.

National veterinary labs like Antech and Idexx use standardized equipment that returns consistently reliable results, so if you’re having your pet tested for giardia, I recommend asking your vet whether he or she tests in-house or sends samples out for analysis.

Another tricky issue with diagnosing giardia is that the parasite isn’t shed every time your pet poops. This means there can be cyst-free stool samples from infected animals. If one of these samples happens to be the one collected for analysis, it won’t show any evidence of giardia, even though your pet is infected.

I 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 a fecal flotation test because it checks for the presence of giardia antigens. A fecal float only detects giardia cysts, which may or may not be in the particular stool sample being tested.

Unfortunately, many vets don’t routinely run the ELISA or PCR test and instead, use only stool sample results that may or may not pick up evidence of infection. So make sure to ask your vet for a fecal antigen test in addition to a fecal float.

Resolving an Infection

The giardia parasite is becoming resistant to many anti-protozoal drugs, which means more and more pets are becoming what we call persistent carriers of the infection.

What I do in my practice is run monthly fecal float tests for three to four months after completion of treatment, sometimes followed by an ELISA test to make sure the infection is fully resolved. The ELISA test can be giardia-positive for up to six months after treatment because it takes awhile for the antigens to clear out of the bloodstream. This is why I don’t run them immediately after treatment completion.

A few fecal floats will give you and your vet the most accurate information about whether the infection has been successfully treated. The reason for more than one test is, again, because giardia cysts aren’t passed in every stool, so a test immediately following treatment may be negative, but a test a week later could be positive. If you stop after one fecal float, it’s very difficult to be absolutely sure the infection is gone.

DOs and DON’Ts for Preventing a Giardia Infection or Recurrence

  • Don’t kennel your pet in close quarters with other animals.
  • Do clean up your pet’s poop outdoors, and don’t walk your dog in areas where other animals relieve themselves.
  • Don’t allow your pet to drink from outdoor water sources.
  • Do drop off a fecal sample with your vet twice a year for testing. This will help identify the presence of a parasitic infection before digestive function is compromised.
  • If your dog’s fecal intestinal parasite analysis is negative, don’t routinely deworm your dog. No dewormer on the market kills every parasite in existence, and since no drug is entirely safe, there are always risks associated with giving medications. The same caution applies when it comes to natural dewormers. Don’t use them “just in case,” assuming one medication or herb will knock out roundworm, hookworm, coccidia, whipworm and giardia. It won’t.