Common Causes of Gastroenteritis

Gastroenteritis is the inflammation of the middle (and longest section) of the gastrointestinal tract (stomach and intestines). In very basic terms, this is an upset stomach. The same as these bouts can happen in people, pets can struggle with some uncomfortable GI symptoms. That being said a little indigestion is very different from a severe medical condition requiring chronic care. Determining the cause of the gastrointestinal upset is the key to treating (or in some cases managing) the pet.

Here are some common causes:


Gastrointestinal upset can be one of the many unpleasant side effects of a parasitic infestation. Hookworms, roundworms, whipworms, giardia and more can lead to diarrhea. A stool sample is analyzed to identify what type of parasite (or multiple parasites) is infecting the GI tract. Then proper treatment, usually medication, is necessary to rid the unwelcome guests from the cat or dog. Many monthly heartworm (a different type of parasite) preventatives also help protect your pet from hookworms and roundworms when given properly. 

Bacteria & Viruses

Cats and dogs investigate their surroundings up close. Unfortunately, this close inspection brings their mucosal linings – think eyes, nose, mouth – close to the object of interest and provides a path for bacteria and viruses to enter the body. Bacterial infections, such as leptospirosis and viral infections such as canine parvovirus, canine distemper, feline panleukopenia and more can be life threatening. These infections are highly contagious among the pet population, especially when an animal is unvaccinated. Many of the highly lethal/contagious infections have a vaccine to prevent a cat or dog from becoming infected. 

Dietary Indiscretion

Ever eat something that just doesn’t sit well with you later? It’s usually no big deal and your back to your old self before you know it. Well the same can happen with our pets – especially those who like to grab a snack from the ground or trash. But in some instances, the effects may be long lasting and require veterinary care. When your pet is having persistent  vomiting and/or diarrhea, or it lasts for more than 24-48 hours, veterinary care is advisable.


Pets should be monitored closely after administering a new medication or a change in dose to an existing prescription. Report vomiting and/or diarrhea to your veterinarian as this could be a sign of a serious side effect. An appropriate course of action will be recommended based on the medication and reason for prescribing. 

Food (new or allergies)

The digestive system of some pets can be very sensitive to a change in diet. It may surprise you to learn that a quick change in food is enough to cause diarrhea in some cats and dogs. When changing foods, slow and steady is the way to go. Gradually increasing the ratio of new food mixed with the old food until the pet is weaned off the old, can help avoid some unpleasant side effects of a simple diet change. This is usually done over the course of about one week. More chronic diarrhea can be part of a food allergy so it is important to speak with your veterinarian about any concerns you may have about your pet’s bowel movements.  

Intestinal Blockage

The digestive tract of cats and dogs can be surprising at what it can pass with seemingly no problem. This is unfortunately not the case in all instances. Once an object is lodged in the digestive tract, serious complications can occur quickly. Vomiting and diarrhea can be only the beginning for some pets. An intestinal blockage can lead to systemic infection (sepsis), necrosis of parts of the intestine and so much more. 

Medical Conditions

In more complex cases, the cause of the vomiting and/or diarrhea in pets may be due to a medical condition such as liver or kidney disease, pancreatitis and more.