Giardia
(Giardia canis)
Holly Nash, DVM, MS
Veterinary Services Department, Drs. Foster & Smith, Inc.
Giardia are protozoa
(one-celled organisms) that live in the small intestine of dogs and
cats. Giardia are found throughout the United States and in many other
parts of the world.
Infection with Giardia is called 'giardiasis.'
There are many things we do not know about this parasite. Experts do
not agree on how many species of Giardia there are and which ones
affect which animals. Veterinarians do not even agree on how common
Giardia infections are and when they should be treated. Generally, it
is believed that infection with Giardia is common but disease is rare.
There is much about the life
cycle we do not know either.
How do Giardia reproduce and how are they transmitted?
Giardia multiply by dividing.
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, although some of them have
not been FDA-approved for that use in dogs. Fenbendazole is an
antiparasitic drug that kills some intestinal worms and can help
control giardia. It may be used alone or with metronidazole.
Metronidazole can kill some types of bacteria that could cause
diarrhea. So if the diarrhea was caused by bacteria, and not Giardia,
the bacteria can be killed and the symptoms eliminated.
Unfortunately, metronidazole has some drawbacks. It has been found to
be
only 60-70% effective in eliminating Giardia from infected dogs, and
probably
is not 100% effective in cats, either. It 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 –
especially
cats.
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.
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, and a
multi-faceted approach is needed.
Treat Animals: Treat all nonpregnant animals with fenbendazole
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. Quaternary ammonium disinfectants
used
according to manufacturer's directions or a 1:5 or 1:10 solution of
bleach
can usually kill the cysts within one minute. Allow the area to dry for
several
days before reintroducing the animals. NOTE: Use extreme caution when
using
quaternary ammonium compounds and bleach solutions. Use proper
ventilation,
gloves, protective clothing and follow your veterinarian's
recommendations.
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.
References and Further Reading
Barr, SC; Bowman, DD. Giardiasis in dogs and cats. Compendium on
Continuing Education for the Practicing Veterinarian.
1994;16(5):603-614.
Barr, SC; Bowman, DD; Frongillo, MF; Joseph, SL. Efficacy of a drug
combination of praziquantel, pyrantel pamoate, and febental against
giardiasis in dogs. American Journal of Veterinary Research.
1998;59(1):1134-1136.
Georgi, JR; Georgi, ME. Canine Clinical Parasitology. Lea &
Febiger. Philadelphia, PA; 1992;59-61.
Griffiths, HJ. A Handbook of Veterinary Parasitology. University of
Minnesota Press. Minneapolis, MN; 1978;21-22.
Hendrix, CM. Diagnostic Veterinary Parasitology. Mosby, Inc. St. Louis,
MO; 1998;19-20.
Meyer, EK. Adverse events associated with albendazole and other
products used for treatment of giardiasis in dogs. Journal of the
American Veterinary Medical Association. 1998;213(1):44-46.
Sherding, RG; Johnson, SE. Diseases of the intestine. In Birchard, SJ;
Sherding, RG (eds.) Saunders Manual of Small Animal Practice. W.B.
Saunders
Co. Philadelphia, PA; 1994;699-700.
Sousby, EJL. Helminths, arthropods and protozoa of domesticated
animals. Lea & Febiger. Philadelphia, PA; 1982;577-580.
Zajac, AM; LaBranche, TP; Donoghue, AR; Chu, Teng-Chiao. Efficacy of
fenbendazole in the treatment of experimental Giardia infection in
dogs. American Journal of Veterinary Research. 1998;59(1):61-63.
