A dog becomes infected by eating the cyst
form of the parasite. In the small intestine, the cyst opens and
releases an active form called a trophozoite. These have flagella,
hair-like structures that whip back and forth allowing them to move
around. They attach to the intestinal wall and reproduce by dividing
in two. After an unknown number of divisions, at some stage, in an
unknown location, this form develops a wall around itself (encysts)
and is passed in the feces. The Giardia in the feces can
contaminate the environment and water and infect other animals and
people.
What are the signs of a Giardia
infection?
Most infections with Giardia are asymptomatic.
In the rare cases in which disease occurs, younger animals are usually
affected, and the usual sign is diarrhea. The diarrhea may be acute,
intermittent, or chronic.
Usually the infected animals will not lose their appetite, but they
may lose weight. The feces are often abnormal, being pale, having a
bad odor, and appearing greasy. In the intestine, Giardia
prevents proper absorption of nutrients,
damages the delicate intestinal lining, and interferes with digestion.
Can Giardia of dogs infect people?
This is another unknown. There are many species of Giardia,
and experts do not know if these species infect only specific hosts.
Sources of some human infections have possibly been linked to beavers,
other wild animals, and domestic
animals. Until we know otherwise, it would be wise to
consider infected animals capable of transmitting Giardia to
humans.
You may have heard about Giardia outbreaks occurring in
humans due to drinking contaminated water. Contamination of urban
water supplies with Giardia is usually attributed to (human)
sewage effluents. In rural settings, beavers most often get the blame
for contaminating lakes and streams. Giardia outbreaks have
also occurred in day care centers fueled by the less than optimal
hygienic practices of children.
How do we diagnose giardiasis?
Giardiasis is very difficult to diagnose because the protozoa are
so small and are not passed with every stool. Tests on serial stool
samples (one stool sample every day for three days) are often required
to find the organism. Special diagnostic procedures, beyond a routine
fecal examination, are necessary to identify Giardia. The
procedures we use to identify roundworms and hookworms kill the active
form of Giardia and concentrate the cyst form.
To see the active form, a small amount of stool may be mixed with
water on a microscope slide and examined under high magnification.
Because these forms have flagella, you can see them move around on the
slide. The active forms are more commonly found in loose stools. If
you ever have the opportunity to see the active form of Giardia
under the microscope, take it! It is an interesting-looking creature.
It is pear-shaped and its anatomy makes it look like a cartoon face,
with eyes (which often look crossed), nose, and mouth. Once you see
it, you will not forget it.
Cysts are more commonly found in firm stools. Special solutions are
used to separate the cysts from the rest of the stool. The portion of
the solution that would contain the cysts is then examined
microscopically.
In spring, 2004, a diagnostic test using ELISA technology became
available. This test uses a very small fecal sample, and can be
performed in 8 minutes in a veterinarian's office. It is much more
accurate than a fecal examination.
We have done the tests, now what?
Now we come to how to interpret the test results. It can be a
dilemma for your veterinarian. What you see (or do not see) is not
always a correct indication of what you have. A negative test may mean
the animal is not infected. However, few, if any, laboratory tests are
100% accurate. Negative test results can also occur in some infected
animals. If a negative test occurs, your veterinarian will often
suggest repeating the test.
What about a positive test? That should not be hard to interpret,
right? Wrong. Giardia can be found in many dogs with and
without diarrhea. If we find Giardia, is it the cause
of the diarrhea or is it just coincidence we found it? The animal
could actually have diarrhea caused by a bacterial infection, and we
just happened to find the Giardia. Test results always need
to be interpreted in light of the signs, symptoms, and medical
history.
If we find Giardia, how do we treat
it?
Here we go again; treatment is controversial too. There is a
question about when to treat. If Giardia is found in a dog
without symptoms should we treat the animal? Since we should not know
if G. canis can infect man, we often err on the side of
caution and treat an asymptomatic infected animal to prevent possible
transmission to people.
If we highly suspect infection with Giardia, but can not
find the organism, should we treat anyway? This is often done. Because
it is often difficult to detect Giardia in the feces of dogs
with diarrhea, if there are no other obvious causes of diarrhea (e.g.;
the dog did not get into the garbage several nights ago) we often
treat the animal for giardiasis.
There are several treatments for giardiasis; some of them have not
been FDA
approved to treat giardiasis in dogs. Metronidazole is one of these,
but is the old standby. The nice thing about this drug is that it also
kills some types of bacteria that could cause diarrhea. So if the
diarrhea was caused by bacteria, and not Giardia, we still
kill the cause of the diarrhea and eliminate the symptoms. Makes us
look pretty sharp! Unfortunately, metronidazole has some drawbacks. It
has been found to be only 60-70% effective in eliminating Giardia
from infected dogs. In some dogs, it can cause vomiting, anorexia,
and some neurological signs. It also can be toxic to the liver
in some animals. It is suspected of being a teratogen (an agent that
causes physical defects in the developing embryo), so it should not be
used in pregnant animals. Finally, it has a very bitter taste and many
animals resent taking it.
Quinacrine hydrochloride has been used in the past, but is not very
effective and can cause side effects such as lethargy, vomiting,
anorexia, and fever.
A newer drug, albendazole, has been shown to be 50 times more
effective than metronidazole and 10-40 times more effective than
quinacrine hydrochloride in killing Giardia in the
laboratory. It has not been approved for use in dogs. Some serious
side effects of albendazole have been noted, including injury to the
bone marrow. Since it may also cause birth defects, it should not be
used in pregnant animals.
In a small study, fenbendazole, which has been approved for
treatment of roundworm,
hookworm,
and whipworm
infections in dogs, has been shown to be effective in treating
giardiasis in dogs. It is safe to use in puppies.
A combination of praziquantel, pyrantel pamoate, and febantel has
also been shown to decrease cyst excretion in infected dogs.
This table summarizes the information above.
But now we come to yet another unknown. It is possible these
treatments only remove the cysts from the feces but do not kill all
the Giardia in the intestine. This means even though the
fecal exams after treatment may be negative, the organism is still
present in the intestine. This is especially true of the older
treatments. So treated animals could still be a source of infection
for others.
How can I prevent my pet from becoming
infected with Giardia?
The cysts can live several weeks to months outside the host in wet,
cold environments. So lawns, parks, kennels, and other areas that may
be contaminated with animal feces can be a source of infection for
your pet. You should keep your pet away from areas contaminated by the
feces of other animals. This is not always easy.
As with other parasites of the digestive system, prevention of the
spread of Giardia centers on testing and treating infected
animals and using sanitary measures to reduce or kill the organisms in
the environment. Solutions of Lysol, bleach, and quaternary ammonium
compounds are effective against Giardia.
How do I control Giardia in my
kennel?
Infection with Giardia can be a big problem in kennels.
Veterinarians at Cornell University have developed a specific
protocol. They recommended a four-pronged approach.
Treat Animals: Treat all nonpregnant
animals with fenbendazole or albendazole for 5 days. On the last day
of treatment, move them to a holding facility while a clean area is
established. When the animals are moved back to the clean area, treat
them once again with a 5-day course of fenbendazole or albendazole.
Decontaminate the Environment: Establish
a clean area. If possible, this can be the whole facility. Otherwise,
create a few clean runs or cages, separate from the others. Remove all
fecal material from the areas since the organic matter in feces can
greatly decrease the effectiveness of many disinfectants. Steam clean
the area and then clean it with a quaternary ammonium disinfectant
according to the manufacturer's directions. These solutions will
generally kill the cysts within one minute. Then let the area dry for
several days before reintroducing the animals.
Clean the Animals: Cysts can remain
stuck to the haircoats of infected animals. So during treatment and
before moving the treated animals to the clean area, they should be
regularly shampooed and rinsed well. Especially concentrate on the
perianal area.
Prevent Reintroduction of Giardia:
Giardia can be brought into the kennel either by introducing
an infected animal or on your shoes or boots. Any new animal should be
quarantined from the rest of the animals and be treated and cleaned as
described above. You should either use disposable shoe covers or clean
shoes/boots and use a footbath containing quaternary ammonium
compounds to prevent people from reintroducing Giardia.
Remember, Giardia of dogs may infect
people, so good, personal hygiene should be used by adults when
cleaning kennels or picking up the yard, and by children who may play
with pets or in potentially contaminated areas.
