[Cagdu] FW: giardia infection in dogs

Sun Nov 4 14:15:28 PST 2007

Subject: giardia infection in dogs

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.

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