1. Diarrhea in Dogs
Giardia is one common cause of diarrhea in your dog
By Joe Bartges
DVM
University of Tennessee
Giardia is a common cause of diarrhea in children in day cares and in adults
that hike and camp — it is also common among cause of diarrhea in our
sporting dogs, too.
Giardiasis refers to an infection caused by Giardia, which is a type of onecelled parasites classified as protozoa. They are found in the intestines of
many animals including dogs, cats, some wildlife, and human beings.
Dogs become infected by ingesting cysts of the organism. This may occur
with contaminated water or on the ground, through eating contaminated
food, through diarrhea, or even from dogs that shed the organism, but do not
have any clinical signs (called carriers).
Eaten giardia cysts release trophozoites (above), which cause an infection.
The cysts are infective as soon as they are passed, unlike other parasites
where a period of time is required for it to become infective. Once eaten, the
cyst releases trophozoites (see picture), which causes the infection. Cysts are
then produced by the trophozoites, which contaminates the environment.
The most common clinical sign of an infection with Giardia is diarrhea,
which occurs about 2 weeks after infection. Usually the diarrhea is not
severe, but it can be. The stools are typically light colored, greasy, and soft.
Sometimes dogs strain and have mucous in their feces. Some dogs may not
have diarrhea even though they are infected and passing Giardia in their
feces. These dogs are carriers for infection.
Diagnosis is based primarily on identification of the organism in feces.
Although an examination of a direct smear may show the trophozoites, it is

2. not very accurate. Spinning a fecal sample down with zinc sulfate is a better
test. The infective cysts are identified by this method. Performing the zinc
sulfate centrifugation test several times over a few days increases its
accuracy. There are ELISA tests available, but they are not as accurate and
are more costly.
There are several medications that can be used to treat Giardia in dogs. Most
commonly, Metronidazole, Fenbendazole, Albendazole, and Furazolidone
are used. These drugs are given by mouth to dogs, one to two times a day,
for 2 to 10 days depending on the medication used. They are generally safe;
however, Albendazole may cause bone marrow suppression and should not
be given to pregnant dogs and Metronidazole can cause neurologic signs
(such as seizures) in a low percentage of dogs. Therefore, fenbendazole is
the preferred treatment.
Dogs should be bathed in order to remove cysts that may be adhered to their
fur. Areas where the dog(s) inhabit including bedding should be cleaned.
Disinfectants containing quaternary ammonium compounds have been found
to kill Giardia cysts at dilutions of 1:704. Efficacy of killing is increased by
prolonged contact time; therefore, disinfectant solution should be left for 20
to 30 minutes before being rinsed off.
About Joe Bartges
Disinfecting grassy areas is impossible. These areas should be regarded as
contaminated for at least a month after infected dogs had last access. With a
large kennel, it may not be feasible to test all dogs. Dogs with diarrhea
should be separated from other animals including exercise, feeding, and
eating areas. All dogs in a kennel whether they have diarrhea or not should
be treated.
Preventing infection can be difficult because dogs may pick up Giardia from

3. the environment, from the water, and from other animals (including dogs,
humans, and wildlife). In areas where Giardia is prevalent, new dogs should
be quarantined before entering into a kennel. They should also be tested as
part of routine preventative care. Dogs that develop diarrhea especially in a
kennel situation should be isolated, tested, and treated.
Keep in mind that Giardia can be spread from dogs to human beings and
from human beings to dogs. Good hygiene should be practiced.