Rob Hilsenroth, DVM
Diarrhea is a common condition that almost every dog owner will
experience at some point -- in the dog, not necessarily the owner.
Most often, the condition is inconvenient but brief, lasting only
a day or two. Diarrhea that lasts longer than a few days or is
particularly severe (with the dog showing other signs of illness
such as lethargy, vomiting, or a fever) can indicate a more serious
refers to any condition that results in an increased fluid component
to the stool. The condition can originate in either the small
or large intestine (also called the colon) and, depending on the
origin, the characteristics of the stool are different. Small
intestinal diarrhea is characterized by large volumes of watery
stool and can be accompanied by the other signs of illness described
above. In contrast, dogs with large intestinal diarrhea produce
small amounts of stool and have increased urgency. These dogs
may also have blood and/or mucus in their feces. Large intestinal
diarrhea is often referred to as colitis, which means inflammation
of the colon.
is caused by any one of a variety of injuries that usually involve
the innermost lining of the colon (called the mucosa). The mucosa,
as the name suggests, has numerous mucus glands that protect the
colon from injury and lubricate the passage of feces. The main
functions of the colon are to absorb water and store feces until
the animal defecates. In dogs with colitis, water is not effectively
absorbed, and the ability of the colon to store feces is impaired.
Excessive amounts of mucus, and even blood, are often passed with
the feces of dogs affected with colitis because of damage to the
protective mucosa lining.
in the colon can decrease the movement of the colon. The colon
normally moves the feces slowly back and forth, enabling maximum
absorption of fluids. When this movement is abnormally slowed,
the contents pass too quickly through the colon and diarrhea ensues.
are many different causes of canine colitis. Diet, parasites,
bacterial infections, and even stress are among the more common
causes of colitis in dogs. Fiber-responsive colitis describes
large bowel diarrhea that resolves by adding fiber to the diet.
In some instances, hypersensitivity or allergic reactions to certain
components in the diet can cause a disease called inflammatory
bowel disease (IBD) of the colon.
another common cause, are parasites that inhabit the large bowel
and attach to the mucosa. These worms interfere with the colon's
ability to absorb water, and thus cause diarrhea.
bacteria can also cause colitis. These bacteria normally live
in the colon but, when conditions are right for these bacteria
to overgrow, colitis develops. A species of bacteria called Clostridium
perfringens is an extremely common cause of colitis in dogs. C.
perfringens causes inflammation of the colon by producing a toxic
substance called an enterotoxin. This toxin acts directly on the
colon mucosa, causes the escape of fluid and salts (also called
electrolytes), and results in decreased movement, which produces
general, colitis is not difficult to diagnose, because the clinical
symptoms are very specific for large bowel inflammation. As mentioned
above, those symptoms include straining to defecate, production
of scant amounts of watery feces that may contain mucus and/or
blood, and increased urgency to defecate. The causes of colitis,
however, can be more challenging to uncover. Your veterinarian
may recommend trial diets with increased fiber or hypoallergenic
diets to identify fiber-responsive colitis or IBD. A stool examination
may reveal eggs of whipworms, indicating the need for a deworming
it's necessary for your veterinarian to see the inside of the
colon, directly, by using an instrument called an endoscope. He
or she can then take small biopsies of the colon for microscopic
examination. Colitis caused by C. perfringens is a diagnostic
challenge because these bacteria are normal inhabitants of the
colon. Thus, determining if the bacteria are truly the cause of
the colitis is difficult. Often, veterinarians must administer
antibiotics based on their clinical suspicion of C. perfringens
Animal Foundation is supporting a study to uncover a more definitive
way to diagnose C. perfringens infections that commonly cause
colitis in dogs. Dr. Stanley Marks of the University of California-Davis'
School of Veterinary Medicine is working to design a "better
mousetrap" for catching C. perfringens in the act of causing
disease. In the study entitled, "Diagnosis and Epidemiology
of Disease Caused by Enterotoxigenic Clostridium Perfringens Type
A in Dogs," Dr. Marks and his colleagues are working to establish
a variety of tests that can be used together to more accurately
diagnose this disease.
tests include counting spores produced by the organisms in feces
and measuring the amount of enterotoxin present in the feces.
This should decrease the number of dogs that receive antibiotics
unnecessarily, and will also help veterinarians uncover the actual
cause of colitis in many patients. As veterinarians are better
able to rule out C. perfringens as the causative agent in dogs
with colitis, they will also be able to more rapidly identify
the true cause and provide these patients with appropriate therapy.