Third Street Veterinary Hospital, PC
McMinnville, Oregon 97128
Office phone: (503) 472-9418
Giardia
Infection in Dogs
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.
Treatment
The
most common drug used to kill Giardia
is metronidazole, an antibiotic-type drug.
It is given for 5-7 days. Other
drugs are also used if diarrhea and dehydration occur. If metronidazole is not effective, others
are available.
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.