What are Giardia?
Giardia are sometimes confused with “worms” because they invade the gastrointestinal tract and can
cause diarrhea. Giardia 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.
How did my dog 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 is able to pass
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.
How is giardiasis diagnosed?
Giardiasis or infection with Giardia is 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 more accurate than the stool exam, but it may require several days
to get a result from the laboratory.
How is giardiasis treated?
The typical drug used to kill Giardia is metronidazole, an antibiotic. It is normally given for 5-7 days
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 also cause diarrhea in humans. Therefore, environmental disinfection is important. The
use of diluted chlorine bleach at 1:32 or 1:16 dilutions (one cup in a gallon or 500 ml in 4 liters of
water) is effective in killing the cysts. Giardia cysts are very susceptible to drying. We recommend
thoroughly cleaning the pet’s areas and then allowing it to dry for several days before reintroducing
This client information sheet is based on material written by Ernest E. Ward Jr., DVM
© Copyright 2002 Lifelearn Inc. Used with permission under license. January 9, 2008.
Animal Clinic, PA