Download Common Causes of Diarrhea Viruses Parasites Bacterial Overgrowth

Common Causes of Diarrhea
By Jocelynn Jacobs, DVM
Diarrhea and competitions go hand in hand with some performance dogs. And if your
dog has diarrhea at an event, it can be both embarrassing and frustrating. They may have
normal, healthy stools at home, but once at the event (or after a few days of competition),
their stools literally fall apart. Many things cause diarrhea in dogs – the most common
include viral infections, intestinal parasites, small intestinal bacterial overgrowth, other
intestinal conditions, stress, and diet.
Viruses
There are many intestinal viruses that cause diarrhea – parvovirus, coronavirus and
rotavirus are the most common. Viral diarrhea can be particularly dangerous, as in the
case of parvovirus infection since it infects, damages, and kills normal intestinal lining.
Dogs infected with parvovirus have severe, bloody diarrhea that can be fatal if not
quickly given supportive and symptomatic care. Coronavirus and rotavirus infections
also damage lining of the small intestine, but not as severely as parvovirus infection.
However, if concurrent with other types of intestinal disease, they may be harder to
overcome.
Vaccines are available to develop protective immunity against both parvovirus and
coronavirus infections, but currently there are none against rotavirus infections.
Parasites
There are many different species of worms that live in the digestive tract of the dog.
Roundworms, hookworms, tapeworms, coccidia, and giardia, are just a few. Intestinal
worms can have a detrimental effect on your dog’s ability to properly absorb and digest
nutrients, and can cause diarrhea if they are present in sufficient numbers.
Many parasites physically damage the lining of the digestive tract. Because of the
propulsive movements of the small intestine, many worms latch on to the intestinal wall
of their host so they won’t be swept away with food material. This results in
inflammation of the lining and inability to digest and absorb nutrients properly which can
result in diarrhea.
Bacterial Overgrowth
Bacteria is normally found in the intestinal tract of dogs. There are good species of
bacteria, such as lactobacillus, and harmful bacteria, such as salmonella or certain strains
of E. coli. Good bacteria are important because they help with digestion and provide
nutrients for healthy intestinal lining. Harmful bacteria may be introduced to the
intestines by feeding infested or spoiled foods, or by eating bacterial-contaminated
objects from the environment. Many dogs have some harmful strains of bacteria present
in the intestines but don’t become ill. However, during times of stress or infection with
other intestinal diseases, harmful bacteria counts can replicate to high levels, and can kill
off or crowd out the beneficial bacteria. This condition is known as small intestinal
bacterial overgrowth (SIBO).
SIBO is more common in dogs than most realize. A study done in 1995 documented 41
of 80 dogs (51%) representing 23 different breeds had SIBO in conjunction with chronic
diarrhea.1 Dogs with SIBO can have many different clinical signs associated with
malabsorption such as weight loss, diarrhea, flatulence (gas), anorexia, coprophagy
(eating stools), and an increased appetite. Diagnosing dogs with SIBO can be difficult
because there is no easy test to determine the levels of harmful bacteria present in the
intestines. Thus many veterinarians must rule out all other causes of diarrhea before they
can diagnosis SIBO as the cause of diarrhea and malabsorption.
Other Diseases
Certain types of intestinal cancer, metabolic diseases, and allergies can also cause
diarrhea. Inflammatory bowel disease (IBD) is another fairly common cause of diarrhea
in dogs. In IBD, the intestinal lining is inflammed and filled with many different types of
white blood cells. Although small numbers of these cells are beneficial, when in large
numbers, the intestinal lining becomes irritated which results in diarrhea.
Stress
Stress also can cause diarrhea. Anxiety causes the sympathetic nervous system to
increase intestinal motility. When the intestines move food through too quickly, nutrients
are not absorbed properly. Dogs that are under stress for long periods of time may have
chronic diarrhea and weight loss.
Nutrition
Even your dog’s diet can cause diarrhea. Changing from one diet to another can cause
intestinal upset and diarrhea if not done gradually over a period of a week. Different
brands of dog foods have different protein, fat, carbohydrate, and fiber sources, and the
intestines need time to acclimate to a new diet.
Some diets are too high in fat for particular breeds or individual dogs and that can cause
diarrhea. If your dog develops diarrhea while on a high fat diet, feeding a lower fat diet
will usually resolve the problem.
There are many different causes of diarrhea in dogs. Identifying and eliminating the
cause and healing the intestines through diet and medication are proper steps in resolution
of the problem.
References:
1. Rutgers HC et al. Small intestinal bacterial overgrowth in dogs with chronic intestinal
disease. J Am Vet Med Assoc. 1995;206:187-193.