Feline Inflammatory Bowel Disease: Nature and Treatment

The inflammatory bowel diseases are the most common cause of chronic vomiting and diarrhoea in cats, and refer to a group of diseases. The term Inflammatory Bowel Disease, or IBD, is applied to a group of poorly understood gut pathologies that are considered to be a consequence of uncontrolled intestinal inflammation in response to a combination of elusive factors that may involve the diet, the environment, the gut microflora and dysregulation of the immune system in susceptible cats.

 

The main hypothesis for the cause and development of human IBD is that there is a dysregulation of the mucosal immune responses to intestinal microflora and/or dietary antigens.¹ This same abnormal immune response to dietary antigens is often suspected in feline IBD. Recent investigations have focused on attempts to better define the immunopathogenisis of the disease.²

 

The absorption of digested food happens in the small intestine, mainly in the first two parts, the duodenum and the jejunum. The walls of these parts of the digestive system form tiny finger-like projections called villi with deep crypts between them. These villi are lined by cells called enterocytes, which work to absorb nutrients and pass them in to the blood stream to nourish the body. The importance of these cells can not be overstated. These cells are born in the base of the villi, known as the crypts, and travel to the top of the villi where they are shed off, constantly being renewed as in their short life, they work incredibly hard.

 

The changes seen in the intestines of a cat with IBD include clear architectural changes. The villi change their shape and become flat and blunted, fusing together and decreasing the surface area available for absorption of nutrients. Inflammatory infiltrate fills the crypts and flattens the wall of the gut. The cells lining the villi, the all important enterocytes, can no longer function properly. The integrity of the gut mucosa is damaged, and results in increased permeability to toxins from the gut lumen and increased bacterial translocation.

 

All of this damage leads to chronic vomiting and diarrhoea as the ability of the intestines to digest food is impaired.

 

 

The diagnosis of IBD requires the comprehensive exclusion of potential causes of gastrointestinal inflammation, including intestinal parasites, small intestinal bacterial overgrowth, bacterial enterocolitis, dietary intolerances and neoplasia.

 

To make a diagnosis of IBD, three features are normally present:

A scoring system is in use in clinical practice for defining the severity and prognosis of IBD, known as the feline chronic enteropathy activity index.³ It grades cats on: their attitude and activity levels; appetite, from normal to severely decreased; frequency of vomiting, from none to more than three times per week; faecal quality, from normal to diarrhoea to faecal blood and mucus; degree of weight loss, from 0 to >10%; and also includes appearance of endoscopic lesions and total protein levels. The index is useful in assessing a cat's response to dietary change and treatment protocols.

 

Histopathological evidence is usually obtained by examining a sample of tissue from a biopsy of the cat's gut. Histopathological diagnosis is not straightforward, especially in cats, as the differentiation of lymphosarcoma and IBD can be difficult, if not impossible on a routine section.⁴ The surprising realisation in cats is that the prognosis for IBD may not be very different to the prognosis for lymphoma.⁵ A sequel to chronic IBD can be intestinal lymphoma. These tumours may occur because of the notorious habit of cats to develop tumours at sites of chronic inflammation.⁶

 

 

The main purpose of having a digestive system is to be able to digest and absorb food. Without a healthy gut flora, the digestive system cannot fulfil this function. Anatomical integrity of the digestive tract, its functionality, ability to adapt and regenerate and ability to defend itself are directly dependent on the gut flora. It is established that the density and composition of the mucosal flora is related to the presence and severity of intestinal inflammation in cats, and suggests that mucosal bacteria are involved in the cause and development of feline IBD.⁷

 

It is hypothesised that IBD could be a variable response to a specific pathogen or an inappropriate or excessive immunological response to normal luminal micro-organisms. The whole length of the digestive tract is coated with a tough bacterial layer providing a natural barrier against invaders, undigested food, toxins and parasites. These indigenous bacteria produce antibiotic-like substances, anti-funghal volatiles, anti-viral substances and they engage the immune system to respond appropriately to invaders. Without well functioning gut flora the gut wall is unprotected and malnourished. Normal gut flora provides a major source of energy and nourishment for the cells lining the digestive tract.⁸

 

It is increasingly clear that dietary influences on the intestinal flora are involved in health and disease.⁹ It is likely that through interaction with the gut flora, certain diets could protect against the development of IBD whilst other diets actually predispose to the development of IBD. In the management of IBD it is prudent to select diets with a high digestibility. Information on the bioavailability of nutrients for cats and dogs is particularly lacking. The most commonly accepted methods of determining bioavailability of nutrients have not been validated for the cat.¹⁰

 

 

Let's look at diet as a trigger for IBD in cats. Our knowledge of nutrient requirements in cats is still incomplete, although a cat's basic nutrient requirements are amply present in the tissues of their prey animals. Most household cats no longer hunt but are instead fed commercially prepared foods. These foods are rich in plant-derived nutrients because to supply cats with all-animal diets is seen as significantly more expensive. The trend has been to make foods with greater proportions of vegetable based products and to supplement them with the necessary nutrients.¹¹