Normal feline faeces are brown and well formed. If a cat is suffering from diarrhoea, the faecal consistency becomes soft or even watery, and the colour may also change to lighter or darker than normal. There may also be fresh blood or mucus in the faeces. The cat's pattern of defecation will also change and the cat may strain on the litter tray. These are important signs to look out for and will help in determining the cause of the diarrhoea.

Causes of diarrhoea
Diarrhoea can be caused by diseases either within (eg, infections) or outside (eg, liver or kidney disease) the gastrointestinal tract. In young cats diarrhoea is most often caused by:

• Diet: In nursing kittens, overfeeding (either feeding too frequently or giving too much milk at each feed) is a common reason for developing explosive diarrhoea. When hand-rearing a kitten, the use of foods not designed for the cat, or overfeeding are common mistakes which can lead to diarrhoea. Equally, too little milk from a queen can cause underdevelopment of the intestinal tract, resulting in diarrhoea. After weaning, sudden changes in diet can also cause diarrhoea. Some kittens develop lactose intolerance (lactose is a component of milk) and will develop diarrhoea if given milk. Playful kittens may also eat things they are not supposed to and this may cause upset too.

• Infectious causes: Viruses, bacteria or parasites (eg, worms) can all be causes of diarrhoea. When this is the case, it will often affect more than one kitten in a litter or may affect other cats in the household. Parvovirus (panleucopenia), coronavirus and rotavirus infections are common viral causes of diarrhoea. Salmonella and campylobacter are two bacteria that can cause diarrhoea. Of the parasites, roundworms, hookworms and protozoa (eg, giardia) can all cause diarrhoea. However, in most cases young cats will show signs of failing to thrive rather than diarrhoea.

In adult cats the most common causes of diarrhoea are:

• Inflammatory bowel disease - this is often responsive to diet
• Dietary intolerance
• Infectious diseases, eg, giardia
• Tumours
• Systemic diseases, eg, hyperthyroidism

Signs of diarrhoea
The signs that the cat shows will depend very much on which part of the intestine is affected. In cats where the diarrhoea is caused by a problem in the small bowel, there will be large volumes of watery diarrhoea and they will lose bodyweight. In large bowel diarrhoea, cats will pass small amounts of soft faeces, occasionally containing some fresh blood or mucus. Cats will defecate more frequently and will probably strain when doing so. However, often the signs the cats show will be a combination of the both of these.

It is easy to monitor the cat's stools if it is the only cat in a household and uses a litter tray. However, in cats that go outside, or in a multi-cat household, it can be much more difficult to ascertain what is going on. However, if the diarrhoea becomes severe, even outdoor cats will start having accidents in the house because they cannot get outside in time. There may also be soft faeces stuck to the fur under the tail. It is best to isolate a cat from others in the household if you suspect it has diarrhoea problems. Vomiting is also a common sign in cats that have gastrointestinal tract problems. Some cats may start drinking a little more to make up for the fluid lost through diarrhoea.

Diagnostic tests
Your veterinary surgeon will examine your cat and after asking various questions will decide if further tests are necessary. If the diarrhoea has developed recently, and the cat is still bright and alert, the vet may only need to treat the symptoms and the problem may resolve. If the diarrhoea is more chronic (lasts longer than four weeks) or if other clinical signs are present, additional diagnostic tests are often required to find the underlying cause.

Blood and urine tests are often carried out to rule out diseases outside the gastrointestinal tract (such as hyperthyroidism, liver disease, kidney disease) and to determine whether the cat has been infected with feline leukaemia or feline immunodeficiency viruses. Blood tests are also sometimes used to assess the function of the gut and the pancreas.

Faecal samples can be examined for parasites such as worms and can be cultured to find abnormal bacteria. Often examination of more than one sample is necessary to confirm or rule out an infection. Radiographs (X-rays) and ultrasound are often used to examine the gastrointestinal tract and to detect abnormalities. Sometimes biopsies of the gastrointestinal tract are needed to make a diagnosis. The stomach, first part of the small intestine and the large intestine can be examined using an endoscope and, if required, tiny biopsies can be taken using special forceps which pass down through the endoscope. This can provide an alternative to taking biopsies at the time of a surgical operation, but this too is necessary in some cases.

Treatment
Treatment is tailored to dealing with the underlying cause of the problem (eg, appropriate drugs to eliminate parasites or other infections). If a cat suddenly develops diarrhoea but is otherwise bright, fasting for 24 hours may be all that is required and the disease is often self-limiting. During this time the cat may be prescribed a solution to rehydrate it (provided it is not vomiting). After fasting, a bland, highly digestible, low fat diet is usually recommended. This can consist of chicken or turkey with some baby rice cereal. Initially the cat should be fed three to four meals a day to reduce the load on the intestine. The diet can then be gradually changed back to the cat's normal food over the next two to three days. If the cat is very lethargic or dehydrated then intravenous fluid therapy will be given.

In cases of very severe, or long-standing diarrhoea, tests will be needed to determine the cause and the most appropriate treatment. Antibiotics are only useful in the treatment of diarrhoea if a bacterial cause has been found in faecal cultures, or if the intestines are severely damaged. Generally in most cases they are not helpful and can even exacerbate the diarrhoea.

Inflammatory bowel disease is a multi-factorial disease and treatment is prescribed on an individual basis. Diet plays an important role in the treatment. Diets are often prescribed that contain a single novel protein (that is a protein that the cat has not eaten in the past six months) and are well balanced. The cat needs to be kept on this single diet for at least four weeks to judge whether there is any improvement. Additional drugs to control inflammation of the gut may also be necessary.

If cancer is the underlying cause of the diarrhoea this can be treated with surgery and/or chemotherapeutic agents. Treatment depends on the type of cancer and the extent of the invasion into the intestine. In some cases, the cause of the diarrhoea may not be found and drugs can be used to provide symptomatic control of the problem.

Prognosis
Prognosis, of course, depends on the cause of the diarrhoea - diseases which are easily managed with diet and/or drugs carry a good prognosis. In all cases, catching and diagnosing the disease early will prevent long-term changes in the gut which may be irreversible.

Updated November 2008