Dogs and many other animals.
Found worldwide, Giardia is caused
by a protozoan parasite affecting the intestines of both
humans and most types of domesticated animals. While dogs
have a high rate of Giardia infection, few will develop
symptoms. Giardia usually causes clinical signs only
in dogs that have weakened immune systems, in dogs that have
been exposed to an abnormally large number of the parasites,
and in young puppies.
Giardia is transmitted by cysts containing Giardia trophozoites,
which are singled-celled organisms shaped like teardrops.
Infected dogs pass these parasites into the environment
via their feces. Dogs that ingest infected fecal material
may contract the disease, the primary symptom of which
is diarrhea.
Most dogs treated for Giardia will recover
quickly. With proper preventive measures, few dogs
will have a recurrence. A recently introduced vaccine
is available that may aid in the prevention of Giardia infection.
The primary sign is diarrhea that
is usually pale, malodorous, and steatorrheic, or containing
fat. Most puppies and adult dogs infected with Giardia suffer
no loss of appetite but may lose weight with continued
diarrhea.
Typically, an owner will bring a dog
or puppy to the veterinarian because it is having diarrhea.
The diarrhea may be pale in color, have an unpleasant
smell, and contain fat. Most dogs will continue to eat,
but they may lose weight with continued diarrhea.
Giardia is a protozoan organism
that can cause infection in dogs, cats, and humans. The
organisms may be found either as trophozoites that swim
freely in the intestines or as trophozoites housed in
cysts that protect them from the environment and thereby
facilitate their transmission. Animals usually contract Giardia by
coming into contact with the cyst form in the external
environment; the feces of infected animals periodically
contain these cysts. Animals that ingest the infected
feces will take these cysts into their small intestines,
where the trophozoites will excyst, or come out of their
protective housing, and infect the animal by multiplying
within the intestines. Afterwards, many trophozoites
will encyst, or revert to cyst form, before returning
to the external environment within the feces. The cysts
may survive in the environment and infect other animals
for a period of weeks; conversely, trophozoites that
have passed into the feces without encysting will die
quickly and cannot transmit the disease.
Giardia is commonly found either in dogs that have
poorly functioning immune systems or in dogs that have
been grouped together in close quarters and hence have
been exposed to an unusually large number of the parasites.
Consequently, young puppies, older dogs that are sick and
debilitated, and dogs that are kept in kennels are susceptible
to Giardia.
Giardia is frequently diagnosed
by means of a zinc sulfate fecal flotation examination,
in which Giardia cysts and trophozoites may be
identified under a microscope. If trophozoites are seen
moving around on a slide smeared with a mixture of fecal
material and saline solution, the canine will test positive
for Giardia. However, because Giardia cysts
and trophozoites are not always passed into the feces,
a negative result for this examination does not rule
out the possibility of Giardia. Consequently,
for the diagnosis to be definitive, it is necessary for
the veterinarian to periodically examine fresh fecal
samples from the animal over the course of a few days.
There are other tests for the detection of Giardia although
these are generally less expeditious and more expensive
than a fecal flotation examination. An enzyme-linked immuno-absorbent
assay, or ELISA test, may be used to detect Giardia antigens
in a fecal sample but is available only in certain veterinary
hospitals and specialized laboratories. A direct immunofluorescent
test may be used to detect the presence of Giardia cysts
in feces but also requires that a veterinarian send samples
to an off-premises laboratory and await the results
Giardia is a very treatable
condition. Most dogs recover quickly and do not have
additional problems. However, if proper preventive steps
are not taken, it is common for dogs with a previous
history of Giardia to become re-infected.
Dogs contract Giardia by swallowing Giardia cysts
found in the feces of an infected animal. Free-swimming
trophozoites cannot infect an animal with Giardia.
Treatment of Giardia often
involves the use of medications such as fenbendazole
or metronidazole. Fenbendazole in particular has been
shown to be very effective in the treatment of Giardia infections.
Neither of these medications is suitable for pregnant
dogs; there are a number of suitable alternative treatments
available, however, for dogs that are pregnant.
Giardia may be prevented by
the strict sanitation of animal living environments using
cleaning agents approved for the elimination of the parasite.
In kennels and other places that house animals in larger
numbers, routine disinfection of the entire facility
is critical. Dogs should be bathed in order to eliminate
any Giardia cysts they may be carrying in their
coats. The periodic use of de-worming medications such
as fenbendazole may also be effective in preventing the
recurrence of Giardia infection.
A new vaccine was introduced recently that is reported to
aid in the prevention of Giardia lamblia infection.
The vaccine may be given to healthy dogs as young as eight
weeks old. A booster shot is usually given two to three weeks
after the initial vaccination and then yearly thereafter.
The
vaccine prevents or lessens the signs of infection and
the amount of cyst shedding. However, some cyst shedding
may occur in vaccinated dogs, so the preventive measures
discussed above should be observed.
