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 pets.

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.
Giardia
763-689-0095
Cambridge VetCare Animal Clinic
Cambridge, MN
Clinic Hours:
Monday - Friday: 8am - 6pm
Saturday - 8am - 12pm
Sunday - Closed