Giardia: The Tiny Bug That Makes Fido (And Us) Mighty Sick

Some Facts About Giardia:
-Giardia is the most common nonbacterial cause of diarrhea in the United States.
-Giardia is one of the most common intestinal parasites worldwide, infecting up to 20 percent of the world’s population.
-Giardia is most prevalent in developing countries, where infections are associated with poor sanitary conditions.
-Giardia infections are more common in children than in adults.

What Is Giardia:
Giardia are sometimes confused with worms because they invade the gastrointestinal tract and can cause diarrhea. They are not worms; instead, they are one-celled parasites classified as protozoa.

Most dogs that are infected with Giardia do not have diarrhea or any other signs of illness. When the eggs (cysts) are found in the stool of a dog without diarrhea, they are generally considered a transient, insignificant finding. However, in puppies and debilitated adult dogs, they may cause severe, watery diarrhea that may be fatal.

Infection:
A dog becomes infected with Giardia when it swallows the cyst stage of the parasite. Once inside the dog’s intestine, the cyst goes through several stages of maturation. Eventually, the dog is able to pass infective cysts in the stool. These cysts lie in the environment and can infect other dogs. They may also be transmitted through drinking infected water.

Diagnosis:
Giardiasis is sometimes diagnosed by performing a microscopic examination of a stool sample. The cysts are quite small and usually require a special floatation medium for detection, so they are not normally found on routine fecal examinations. Occasionally, the parasites may be seen on a direct smear of the feces. A blood test is also available for detection of antigens (cell proteins) of Giardia in the blood. This test is probably more accurate than the stool exam, but it requires several days to get a result from the laboratory performing the test.

None of the tests for giardiasis are completely accurate. Therefore, some veterinarians choose to treat the dog with one of the safe and very effective medications. If successful, this approach will eliminate the parasite even though a confirmed diagnosis is not made.

Transmission to Humans:
Giardia can also cause diarrhea in humans. Therefore, environmental disinfection is important. The use of chlorine bleach, one cup in a gallon (500 ml in 4 liters) of water, is effective if the surfaces and premises can be safely treated with it.

Sick Puppies Test Positive for Giardia

Meet two darling dachshund puppies, Pinball and Rambo, owned by Susan and Daniel Donaldson.  These brother and sister puppies were purchased from a breeder and checked out well at their first exam.  Within days, Rambo became very lethargic and had diarrhea, and Pinball got significant diarrhea but wasn’t as depressed.  They came in to Care Animal Hospital and were seen by Dr. Tracie Grubb.  She did two different tests on the feces and the samples tested positive for giardia. 

So – what exactly is Giardia?     Giardia is sometimes confused with “worms” because they invade the gastrointestinal tract and can cause diarrhea.  Giardia is a one-celled parasitic species classified as a protozoa.

How do dogs get Giardia?     A dog becomes infected with Giardia when it swallows the cyst stage of the parasite.  Once inside the dog’s intestine, the cyst goes through several stages of maturation.  Eventually, the dog passes infective cysts in the stool.  These cysts lie in the environment and can infect other dogs.  Giardia may also be transmitted through drinking infected water.  Most streams and lakes in Colorado are infected with Giardia. 

How did we diagnose Giardia in these puppies?     At Care Animal Hospital we perform two different tests on fresh stool to try and identify giardial cysts.  One is called a fecal centrifugation test, where the feces are spun in a specially designed centrifuge machine using a specific kind of liquid to help separate the cysts.  The coverslip sitting on the centrifuge tube is placed on a slide and the sample scanned under the microscope looking for cysts.

Recently we obtained another type of test known as an ELISA test – which looks for some of the markers on the outside of the giardial cysts and reacts with a color change.

Both tests miss about 15% of the positive dogs, but they miss a different 15% so using both tests together helps us to be over 90% sure that the dog is infected if we get a positive ELISA test or we identify the cysts under the microscope

How is giardiasis treated?     The typical drug used to kill Giardia is metronidazole (flagyl), an antibiotic that is either a tablet or we can create a liquid for smaller animals.  It is normally given for 8 days (two times a day) to treat giardiasis.  Other drugs are also used if diarrhea and dehydration occur.  If Metronidazole is not effective, other medications may be recommended. 

Can humans become infected with Giardia?     Giardia can cause diarrhea in humans.  If your dog is diagnosed with giardiasis, environmental disinfection is important.  We recommend thoroughly cleaning the pet’s living and sleeping areas and then allowing the areas to dry out for several days before reintroducing pets.  One cup of bleach in 1 gallon of water is effective in killing the cysts. 

Are dogs with giardial cysts always sick?     Most dogs that are infected with Giardia do not have diarrhea or any other signs of illness.  When the dysts are found in the stool of a dog without diarrhea, many times we consider them transient and sometimes do not treat these dogs.  However, as Rambo and Pinball taught us, in puppies and debilitated adult dogs, Giardia may cause severe, watery diarrhea that may be fatal. 

We are happy to report that Rambo and Pinball are currently doing very well.