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Giardia in the Dog
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Giardia
Giardia Cannis
Giardia
Giardia is the genus of a
protozoan parasite that is infectious to both humans and pets all over
the world. Giardia consists of flagellates, which mean they move
by means of several whip-like structures called “flagella.” They live as
a form called a “trophozoite,” or “troph” for short, in the intestine where
it causes diarrhea. In fresh fecal samples, trophozoites can sometimes
be captured. They swim around in a jerky fashion characteristic of flagellates
and appear as a funny face (the two nuclei form the eyes and median bodies
form the mouth).
After a short period of time outside the host’s intestine, the trophozoites
round up and form cysts that enable them to survive environmental conditions
without a host to protect them. The cyst can be dried out to decontaminate
the environment, but if it is cold and wet the cyst can live for many months
with two incompletely formed trophozoites inside, ready to infect a new
host. Contaminated water is the classical source of a Giardia infection.
After having been swallowed, the cyst shell is digested away, freeing
the two trophozoites who go and attach to the intestinal lining. The troph
has a structure called a “ventral disc,” which is sort of like a suction
cup, and this is used to stay attached to the intestine. If the troph wants
to move to another spot, it lifts itself up and swims to a new spot via
its flagella (trophs tend to live in different intestinal areas in different
host species, depending on the host’s diet). If the host has diarrhea, trophs
are shed in the diarrhea, but Giardia may also form cysts within the host
in preparation to be shed. Either form can be found in fresh stool.
After infection, it takes 5 to 12 days in dogs or 5 to 16 days in cats
for Giardia to be found in the host’s stool. Diarrhea can precede the shedding
of the Giardia. Infection is more common in kennel situations where
animals are housed in groups.
How Does Giardia Cause Diarrhea?
No one is completely sure but infection seems to cause problems with
normal intestinal absorption of vitamins and other nutrients. Diarrhea is
generally not bloody. Immune suppressive medications such as corticosteroids
can re-activate an old Giardia infection.
Diagnosis
In the past, diagnosis was difficult. The stool sample being examined
needed to be fresh, plus Giardia rarely show up on the usual fecal flotation
testing methods used to detect other parasites. Traditionally, a fecal
sample is mixed in a salt or sugar solution such that any parasite eggs
present will float to the top within 10 to15 minutes. Some tricks that
have been used to facilitate finding Giardia include:
Being sure to examine a direct smear of the fecal sample (in hope of
finding swimming trophs).
Floating the sample in zinc sulfate, a solution that has been found
superior in getting Giardia cysts to float.
Staining the sample with some sort of iodine under the microscope to
make the Giardia show up easier.
What has made Giardia testing infinitely easier is the development of
a commercial ELISA test kit (similar in format to home pregnancy test kits).
A fecal sample is tested immunologically for Giardia proteins. This method
has dramatically improved the ability to detect Giardia infections and
the test can be completed in just a few minutes while the owner waits.
Giardia shed organisms intermittently and may be difficult to detect.
Sometimes pets must be retested in order to find an infection.
Treatment
A broad spectrum dewormer called
fenbendazole (Panacur®) seems to be the most reliable treatment
at this time. Metronidazole
(Flagyl®) in relatively high doses has been a classical treatment for
Giardia but studies show it to only be effective in 67% of cases. The high
doses required to treat Giardia also have been known to result in temporary
neurologic side effects or upset stomach. For some resistant cases, both
medications are used concurrently; further, a study by Scorza et. al in 2004
found that Drontal® (a combination of praziquantel, febantel, and pyrantel
pamoate) is effective in many cases. The ELISA test for Giardia should go
negative within 2 weeks of treatment indicating success.
Because cysts can stick to
the fur of the infected patient and be a source for re-infection, the positive
animal should receive a bath at least once in the course of treatment.
Not all patients with Giardia actually have diarrhea but because Giardia
is the most common intestinal parasite affecting humans in North America,
treatment is generally recommended for the pet testing positive even if
no symptoms are being shown. The idea is to reduce human exposure.
Vaccine?
A Giardia vaccine made by Fort Dodge Animal Health is on the market
but it is not intended to prevent infection in the vaccinated animal.
Instead the vaccine is licensed as an adjunct to treatment and is used to
reduce the shedding of cysts by the vaccinated patient. This would
be helpful in a kennel situation that is trying to reduce environmental contamination
during an outbreak or where an animal keeps getting reinfected, but it is
not helpful to the average dog whose owner wants to simply prevent infection.
The 2006 American Animal Hospital Association Guidelines
list this vaccine as “not recommended.”
Environmental Decontamination
The most readily available effective disinfectant is probably bleach
diluted 1:32 in water, which in one study required less than one minute
of contact to kill Giardia cysts. Organic matter such as dirt or stool is
protective to the cyst, so on a concrete surface basic cleaning should be
effected prior to disinfection. Animals should be thoroughly bathed before
being reintroduced into a “clean” area. A properly chlorinated swimming pool
should not be able to become contaminated. As for areas with lawn
or plants, decontamination will not be possible without killing the plants
and allowing the area to dry out in direct sunlight.
Copyright
2007 - 2007 by the Veterinary Information Network, Inc. All rights reserved.
This work was originally published by Veterinary Information
Network, Inc. (VIN) and is republished with VIN's permission.
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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.
The above information is simply informational.
It's intent is not to replace the advice of a veterinarian nor to assist
you in making a diagnosis of your pet. Please consult with your own veterinarian
for confirmation of any diagnosis. Your pets life may depend on it.