Diarrhea, causes & concerns

Diarrhea can be caused by MANY different things including, but not limited to:

  • parasites (eg worms, protozoa (ie giardia))
  • bacteria (eg. salmonella, E coli, clostridium)
  • toxicity (eg. chocolate, drugs, indiscretion (an entire turkey, garbage etc)
  • dietary intolerance/allergies

It’s important to note that ‘just the runs’  is certainly not a straightforward issue and is often difficult to determine the exact cause, the most effective treatment, and ultimately how to prevent it.

Importantly, diarrhea can be life threatening and have long lasting health implications, especially in young animals. As an owner it’s important monitor your pet’s bowel movements and keep up with regular deworming & fecal testing (yearly for adult animals). Don’t hesitate to ask us for advice on  any abnormalities that you see (or smell!) as excessive, discoloured (especially blood), mucus, frequent, and various other fecal abnormalities may be more severe. Ultimately, abnormal feces is often a sign of a deeper problem that can cause significant discomfort to your pet who deserves an observant advocate (you!) and prompt treatment (us!)

GIARDIA – we are having somewhat of an epidemic in Vancouver it seems

Giardia (colloquially known as “Beaver Fever” – it IS a disease people can get from giardia positive pets). People more commonly get this disease from drinking unfiltered water wild animals have contaminated BUT if your pet is positive for giardia you can catch it! It

Cysts are resistant forms and are responsible for transmission of giardiasis. Both cysts and trophozoites can be found in the feces (diagnostic stages) (1). The cysts are hardy and can survive several months in cold water. Infection occurs by the ingestion of cysts in contaminated water, food, or by the fecal-oral route (hands or fomites) (2). In the small intestine, excystation releases trophozoites (each cyst produces two trophozoites) (3). Trophozoites multiply by longitudinal binary fission, remaining in the lumen of the proximal small bowel where they can be free or attached to the mucosa by a ventral sucking disk (4). Encystation occurs as the parasites transit toward the colon. The cyst is the stage found most commonly in nondiarrheal feces (5). Because the cysts are infectious when passed in the stool or shortly afterward, individual-to-individual transmission is possible. CDC 2017

Giardia is a flagellated protozoan or single-celled organisms, which are found not only in the small intestine of dogs and cats, but also found in almost all wild animals and in humans. Yep, our rabbit friends are in this bunch!



Giardia is usually in the rivers, ponds, puddles and many other places. The most common route is through water that has been contaminated with feces. Giardia parasite prefers humid and cold environments  (Vancouver seems to be puuuurrrrfect).

Symptoms of Giardia

The majority of Giardia infections are asymptomatic, meaning there are no clear signs that your pet is infected. When and IF symptoms do appear, the most common is diarrhea, which can be acute or chronic. Weight loss or more vague symptoms of generalized lethargy and inappetence, nausea, vomiting are also common symptoms. As giardia interferes with digestion and inhibits the absorption of nutrients, it can inflict long term damage to the intestines and can go undetected for many years. The parasite is the root of many cases of inflammation of the gastrointestinal tract in dogs and not infrequently dogs with chronic diarrhea, malabsorption and other digestive problems which turn out to be giardia positive.

How to diagnose giardiasis?

Giardia looking evil under the microscope

Giardiasis is very difficult to diagnose because the protozoa are very small and do not always come out in feces. Special diagnostic procedures, in addition to routine stool examination, are necessary to identify Giardia.

Not uncommon, sometimes negative test results can occur in infected dogs. If there is a negative test testing is often repeated especially in symptomatic animals.


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 who tests positive even if no symptoms are seen. This is important from a human health perspective as well as to prevent the spread of this disease to other pets.

Treatment typically involves a combination of metronidazole (known as Flagyl in human medicine) and fenbendazole. As these are oral drugs and are not without their drawbacks, side effects, and ultimately should not be taken lightly. At our hospital we think it is important that each patient is treated individually based on their age, condition, life style, living situation. After treatment, pets should be re-tested to determine whether there are still remaining giardia. Unfortunately we are entering a time when drug resistance is more common and we must be vigilant to ensure we are treating cases to 100% resolution to prevent resistant superbugs. Rarely, some pets may require more than one course of antibiotics.

The big clean up & quarantine

Your pets environment will have to be cleaned to prevent spreading to other pets (and you!) and re-infection. This can be a big job and we feel for you.  Using gloves, all feces should be promptly disposed of, especially if it lands in a common area. Washing surfaces (especially floors), putting dishes in the dishwasher on high heat, and bedding on a high heat cycle also are recommended. The water temperature should be above 70 Celsius to kill giardia.  The most readily available effective disinfectant is bleach diluted 1:32 in water, which in one study required less than one minute of contact to kill Giardia cysts. Most swimming pools are chlorinated enough to kill giardia, if that helps with your dilution issues. Organic matter such as dirt or stool is protective to the cyst, so on a concrete surface basic cleaning should be done prior to disinfection. Animals should be thoroughly bathed before being reintroduced into a “clean” area. A good shampoo and thorough drying is sufficient, please no bleach or scalding water.

As this is an easily transmissible disease it is very important to keep your dog away from other pets & susceptible people (especially young children, immunocompromised people, elderly people, pregnant women, etc). Until your pet is not shedding giardia, please avoid kennels, day care, groomers, etc. Giardia lasts several months in cold water or organic matter and thus you may be putting other unsuspecting pets at risk.

As this all can be quite a difficult undertaking, it is recommended to test and treat as early as possible to limit the disease course as well as prevent the spread of the disease. Treated individuals typically stop shedding giardia 2 weeks following treatment initiation but low amounts of giardia can be found in even those treated for many weeks. Thus, the importance of the fecal test after treatment to ensure eradication.

Animal human transmission of Giardia. CDC 2017

How to prevent my dog ​​from becoming infected with giardia?

Giardia cysts can live several weeks to several months outside the host in a wet, cool environment. Grass, ponds, parks or almost anywhere in Vancouver especially around Stanley Park are certainly risky areas for acquiring a giardia infection, for some reason we have seen many cases in 2016 & 2017.

But that shouldn’t prevent you from getting out there and enjoying the beautiful West End, just keep an eye open for abnormal feces and ensure that yearly fecal tests are performed.




Bacterial diarrheas are generally a nuisance for the adult animal but can be lethal to a small puppy, kitten, rabbit, or rodent. Most of these problems stem from contaminated food or fecal contaminated environment. Raw food diets dramatically increase the risk of human exposure.  In general, when it comes to bacterial diarrhea, the smaller and less mature the patient is, the more serious the infection.

Campylobacter species are a group of bacteria capable of causing diarrhea in dogs, cats, humans, and other animals. They have a unique curved appearance under the microscope and are said to be sea gull shaped. They are difficult to isolate as they grow in conditions of low oxygen (making them microaerophilic as opposed to being aerobic or anaerobic bacteria). With regard to pets, Campylobacter are generally a problem for the very young. Puppies and kittens do not have mature immune systems and as they are small, fluid loss from diarrhea can be more significant. Furthermore, puppies and kittens are more likely to be housed in groups where fecal cross­ contamination is common so they may be more likely to become infected than adult animals. Adult animals commonly have Campylobacter organisms living in their intestines but they do not experience any sickness due to it. In humans, Campylobacter infection is a leading cause of gastrointestinal (GI) disease; infected dogs and cats can carry the organism and spread it even if they do not have symptoms themselves. For this reason, pets used for therapy in assisted living communities and similar situations should be screened for Campylobacter by fecal culture before exposure to people with suppressed immunity. Humans are also infected by consumption of contaminated food, water, or raw milk; only 6% of human Campylobacter infections are attributed to dog exposure. That said, exposure to a dog with diarrhea triples a person’s risk for developing enteritis from Campylobacter jejuni or Campylobacter coli. Studies screening pet animals for inapparent Campylobacter infections have found surprisingly high incidences of inapparent infection. In one study, 24% of 152 healthy cats were positive. After one consumes Campylobacter organisms, they travel to the lower small intestine, attach, and begin to multiply. They produce a toxin that destroys the lining of the intestine with the result being a bloody, mucous diarrhea (though occasionally a more watery diarrhea is described). Sometimes a fever results, appetite becomes poor, and vomiting can occur. Incubation is 2 to 5 days. The organism can survive as long as a month in environmental feces. 

Diagnosis is made by seeing the sea gull­ shaped organisms under the microscope; however, there are so many bacterial organisms on a fecal sample that finding the culprit can be tricky. For this reason, a culture is often performed as a more accurate test. Because the organism is microaerophilic, specific culture requirements must be met; the facilities of a reference laboratory are needed. Treatment is with appropriate antibiotics. Erythromycin is currently considered the drug of choice.

Like Campylobacter, the young are more susceptible to salmonella and often come down with a more severe illness because they are smaller and do not have mature immunity.  There is an important exception to the “Salmonella is rare in adult dogs” rule and that is the case of dogs fed a raw food diet. It has become popular to feed raw foods to pets with the idea that a raw food diet more closely approximates the natural diet that the feline or canine body evolved to consume, and thus such a diet should be healthier than commercially prepared foods. In fact, the cooking of food is central to removing parasites, bacteria, and bacterial toxins from food. A recent study evaluating raw food diets found that 80% of food samples contained Salmonella bacteria and that 30% of the dogs in the study were shedding Salmonella bacteria in their stool. Adult dogs are often asymptomatic but any infected animal or person will shed the organism for at least 6 weeks, thus acting as a source of exposure to other animals or people. Salmonella organisms are difficult to remove from the environment and easily survive 3 months in soil. Again, dogs used for therapy around the elderly or children should be cultured for Salmonella. There are two syndromes associated with Salmonella: diarrhea and sepsis. Salmonella bacteria, once consumed, attach to the intestine and secrete toxins. The toxins produce diarrhea that can be severe and even life­ threatening in the young. If this were not bad enough, some Salmonella can produce an even more serious “part two” should these bacteria invade the body through the damaged intestine, causing a more widespread and much more serious infection.. In young animals, the syndrome resulting is similar to that of canine parvovirus

E. Coli may be the most common bacterial organism in the world. It lives in our intestines naturally and covers the world we live in. Unfortunately, some strains of E. coli are not so neighborly and are capable of producing diarrhea via toxin production. Like the other organisms we have discussed, this is a serious problem for the very young and more of a nuisance for adults. There are three main types of unfriendly E. coli: Enterotoxic E. coli, enterohemorrhagic E. coli, and enteropathogenic E. coli. Enterotoxigenic E. coli are a common cause of diarrhea in young animals as well as human infants, and are responsible for the famous traveler’s diarrhea. These bacteria produce E. Coli enterotoxin in the upper small intestine. This toxin, similar to the toxin of cholera, causes the intestine cells to secrete the body’s fluid into the intestine creating spectacular watery diarrhea and what can be life­ threatening dehydration for small pets. Enteropathogenic E. coli simply destroy the intestinal cells where they attach. Diarrhea still results but it creates more damage to the intestinal lining. Enterohemorrhagic E. coli is similar to enteropathogenic E. coli but with more associated inflammation and bloody stool (hence the hemorrhagic part of the name).

It would seem that antibiotics would be the obvious treatment for a bacterial disease, yet for E. coli it is surprisingly controversial. It seems that the use of antibiotics can enhance the synthesis of toxins by these bacteria; plus, oftentimes antibiotic use only serves to make E. coli more resistant in the GI tract. Antibiotics are generally reserved for those animals who seem the most sick or who have evidence of bacterial invasion in the bloodstream. Basically treatment is supportive care until the patient’s immune system regains the upper hand.

In Conclusion Bacterial diarrheas are an especially serious consideration in the very young and in the weak or compromised. It is not unusual for apparently healthy animals to carry these organisms and shed them into the environment and feeding raw foods greatly increases the risk of this kind of latent infection. If you are considering raw food diets, especially if there is someone in the home who is very young or who has a compromised immunity, discuss prevention of these infections with us.


WORMS & other parasites






As always, if you have any questions at all we are here to help.

Dr. Childs