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Giardiosis is the Name of the Disease

Diarrhea, Nausea, and Chronic GI Irritation are the main Symptoms
by Roger Ross, DVM

Another little organism that frequently causes diarrhea in pets is Giardia.  There are lots of different strains and subspecies of this amoeba that differ a little as you go around the world, and every time we humans or our pets get exposed to these creatures, there's the potential for irritation to the stomach or intestines.

For Humans:

When you drink water from streams and ponds and get the runs, it may well have been caused by one of the many strains of Giardia.   (Or Cryptosporidia... see my short comments about this organism on the side bar to your left)

When you travel to exotic locations and get diarrhea after eating the local foods, the cause is more likely to be bacterial (e-coli, samonella, clostridium, etc), but it could be from Giardia

Our intestinal tracts get exposed to these very tiny, microscopic, organisms all the time as we go about our daily lives, just as our respiratory system is constantly inhaling biological particles along with each breath of air. 

The reason we don't usually get diarrhea, though, is that we can usually rely on our body's defense systems to prevent these organisms from multiplying in our tissues.  But there are exceptions and reasons why our defenses don't work 100% of the time.

If our general health is poor; our immune system will be weak

If our intestinal lining (the mucosa) is unhealthy from poor diet, a heavy parasite load (worms), ulcerations, or bacteria, then Giardia organisms will be more likely to establish themselves in the intestinal wall.

If our immune system is not yet mature (babies,puppies, & kittens) or if it is suppressed, over loaded, or worn out due to stress, disease, pregnancy, or old age; then we may not be able to fight off the Giardia as readily.

And finally, if, while traveling or camping, we accidentally expose our immune system to a strain of Giardia our system hasn't seen before, it takes a little time to mount an effective defense.  This may give the organism enough time to multiply enough to cause diarrhea, nausea etc.  Usually the GI upset caused by Giardia is mild and temporary, but occasionally it can be violent and debilitating.

That was fun writing about human beings for a change.

But it's relevant because the same concepts apply to our pets and other animals:  Exposure to this little amoeba is frequent and unavoidable and rarely causes much trouble because of our fairly efficient mammalian immune systems, enzymatic saliva, acidic stomach acid, bile salts, and so forth. 

But every once in a while enough RAMBO or stealth type organisms survive our defenses AND are able to set up house in our intestinal lining and have SEXUAL REPRODUCTION and we all know that means trouble, don't we? 

If the organisms multiply, they cause irritation and inflammation to the bowels and/or stomach leading to different degrees of nausea and diarrhea.

If the problem isn't quickly corrected by the immune system or from treatment, then we sometimes get pets that aren't on death's door step exactly, but who suffer from chronic, mild diarrhea and all the miserable secondary effects of feeling run down, dehydrated, dirty, etc.

To Summarize:

Exposure to Giardia is common, but usually our immune system effectively kills the organism before it causes enough damage to notice.  If not, the resulting diarrhea is usually mild and quickly resolved without treatment.

How often is the diarrhea we see in our pets caused by Giardia?

We're not sure;

Diarrhea is such a common and easily resolved problem that most cases aren't presented to a vet unless the diarrhea is severe, bloody, or not resolved with home remedies.

And there are so many possible causes.

And if we vets do see a diarrhea case, we often don't go to the expense of testing for Giardia.  We often just treat the diarrhea.
Or, even if we suspect Giardia, we often just treat the disease without confirming that Giardia is present.  This isn't being sloppy so much as it's being practical; Here's why:

Even if Giardia is the cause of the diarrhea, it can be very difficult to detect.

Even if Giardia is found, it doesn't necessarily prove that Giardia was the culprit or the only culprit.  Just like in the OJ Simpson trial; just because he was there doesn't proved he killed her.  Maybe it was the pizza boy.  Whoops, I'm off track again.

Because of our fairly efficient immune systems, many diarrhea cases caused by Giardia heal without treatment.

The treatment for Giardia disease, except in complicated cases, is inexpensive and safe. 

At any rate, because of all these factors, we really don't know how often Giardia is the cause of diarrhea in mammals.  My own feeling as a practitioner is that it's a common cause.  For what that's worth.

For those of you that want to know the details, here's the life cycle and more scientific information:  Otherwise skip down to the treatment part.

Giardia spp. are parasitic protozoans (single celled organisms) found in the intestines of many animals, including dogs. This microscopic parasite clings to the surface of the intestine, or floats free in the mucous lining the intestine.

Giardia occurs in two forms: a motile feeding stage that lives in the intestine, and a non-motile cyst stage that passes in the feces.

Encystment occurs as the parasite travels to the large intestine. The cysts are fairly resistant, and can survive for several months as long as sufficient moisture is provided. Mature cysts are usually found in the feces of infected animals. 

That highlights a practical point:  We vets are unlikely to detect Giardia as the cause of diarrhea when we do fecal testing UNLESS there has been time to develop a large number of mature cysts.

Animals become infected by ingesting these cysts which survive in the environment whereever there is moisture.  A pet might ingest them directly from drinking from a puddle, pond, or stream...or simply get them on their paws or coat while walking through damp grass and lick them off while grooming.

These cysts break open in the intestine to release the motile feeding stage (trophozoite). Giardia trophozoites multiply by splitting in half over and over again.  This is known as binary fission or safe sex.

How did my dog get Giardia?
Giardia is transmitted from host to host by ingesting cysts in contaminated feed or drinking water. Cysts may also be found in streams or other water sources. Sometimes the trophozoite stage may also be infective to dogs, but this stage does not survive for very long after being voided in the feces.

Zoonosis: Can I get Giardia from my dog?  And Vice Versus?

We think so.

Clinical signs range from none in asymptomatic carriers, to mild recurring diarrhea consisting of soft, light-colored stools, to acute explosive diarrhea in severe cases.

Other signs associated with giardiasis are:

weight loss
mucus in the stool
anorexia or loss of appetite

Diagnosis is confirmed by finding the cysts or motile stages in feces. But a negative report does not rule out Giardia.  Why? Because cysts are only passed periodically so several fecal examinations may be required to detect this parasite. Several fecal samples, examined over a period of seven to ten days, should be examined before you can be confident of being negative for Giardia.

(Of course, your vet may do things differently)

Treatment is pretty straight forward:

1.  Treatment of the symptoms of diarrhea, nausea etc to make the patient more comfortable.  This may include medications such as kaopectate, bella donna alkaloids, paragoric, Tigan suppositories, Reglan Injections or tabs etc.

2.  Electrolytes and IV Fluids if needed.

3.  Treatment of the parasite:  I use a drug called metronidazole as well as Panacur (fenbendazole).  Using these medications together seem to work much better than either drug alone.  Other possible treatments include quinacrine and albendazole.

4.  Treatment of other pets in the household or kennel if warranted.

5.  Follow up testing and recheck maybe prudent or needed.

On This Page:

A little about the amoebic parasite called Giardia

And a little about another protozoa called

On Other Pages
There is a complete directory of links at the bottom of the page

Our Home or Introductory page about intestinal problems in dogs and cats

Other intestinal parasites:

Round Worms
Hook Worms
Whip Worms
Tape Worms

Other intestinal problems:





Liver Disease


Food Allergies

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Colitis: Chronic problems with the lower bowel

Garbagitis: Acute intestinal upset due to overeating, eating treats, rancid food, and eating inappropriate objects, or eating too much hair.

Diseases people get from pets through worms

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Little boys, little girls, humans of all ages as well as most other mammals can get amoebic dysentery ... diarrhea caused by protozoa prevalent in streams, creeks, rivers, and lakes.  Giardia is one of the little protozoa organisms that frequently causes diarrhea... often chronic in people and pets.
In case you haven't thought about it much, anytime cows, sheep, hogs, deer, coons, skunks, birds, snakes, turtles, fish,  defecate a big percentage of the bacteria and all the other little microscopic organisms that live in the bowels of animals, fish and fowl end up in our waterways. 
Much of this is beneficial to the environment and the cycles of life.  But some of these organisms, including the tiny, single cell organisms known as giardia can cause pretty severe bowel irritation in mammals, especially if we or our pets ingest a strain our immune systems haven't encountered before.  This business of being exposed to strains of bacteria and protozoan organisms like giardia that we haven't encountered before is one of the reasons people and pets often get diarrhea when traveling.
Cryptosporidiosis is a diarrheal disease caused by microscopic parasites of the genus Cryptosporidium. Both the disease and the parasite are commonly known as "Crypto."

Many species of Cryptosporidium exist that infect humans and a wide range of animals. The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very resistant to chlorine disinfection.

While this parasite can be transmitted in several different ways, water is a common method of transmission and Cryptosporidium is one of the most frequent causes of waterborne disease (drinking water and recreational water) among humans in the United States. Water parks and public pools are a common place to pick up this bug.

For veterinarians, Crypto is most commonly a problem in calves.

The problem to pet owners is that the people who work on
dairy farms ... and the cats and dogs that happen to have had contact with dairy or beef farms ... may be carriers of the crypto organism that is then passed along to susceptible pets and people in the suburbs and cities.

For the vast majority of people and pets, Crypto causes a short lived bout of diarrhea that is self curing.

People will probably mistakenly blame the last restaurant they ate in as the cause.

But sometimes the disease is severe, long term, and difficult to control.  Especially if the patient is stressed or has a weak immune system.  I think I've seen this problem several times a year in shelter kittens.

I say, "I think", because Crypto is difficult to detect in the lab.

It's a good thing that most Crypto cases are self curing because there is no approved treatment other than supportive and symptomatic care.
Other Topics on this web site that you might find interesting:

History of Veterinary Medicine; lots of interesting stuff    

A tribute to Dr Harvey Cushing

Where does your pet food come from?

History of the Discovery of Antibiotics

The Human-Animal Bond
Comments & Stories about this topic close to my heart

Cats: Fun or interesting stuff about cats and a discussion about the diseases common in our feline companions to include Leukemia, Feline AIDS, & Cat Scratch Fever.

Dogs:  a hodge podge page of stuff about dogs.

Pet Insurance:
Why I like and recommend Pet Insurance

Zoonotics: Diseases People get from Pets, Worms & other Parasites People get from Pets.