Clinical Conditions

5.3.1 Horse (Figure 5.2)

The small intestine of the horse is susceptible to a variety of inflammatory causes. Bacterial and parasitic infections can be responsible for a serious onset of enteritis.

5.3.2 Ox

Johne’s disease: This is the name given to a disease of the small intestine of ruminants. It is caused by the bacterium Mycobacterium paratuberculosis and is seen most fre­quently in cattle but can affect non-ruminant species. The bacterium invades the small intestine and is transported by the M cells to the Peyer's patches of the ileum (see Section 5.1). Here it is captured by macrophages, but rather than being rendered harm­less, the usual function of the macrophages, the bacteria promote an overgrowth of lymphocytes. As a result, there is thickening of the intestine wall with a serious obstruction to absorption of nutrients. Affected animals lose weight, suffer diarrhoea and die.

5.3.3 Sheep

Johne’s disease: This disease is less common in sheep than in cattle. The pathogen is again Mycobacterium paratuberculosis (M. johnei). In sheep, unlike in cattle, diarrhoea is not usually a feature. The presenting signs are weight loss and loss of condition. The pathogenesis is the same as in cattle, i.e. thickening of the small intestine wall with resulting malabsorption.

5.3.4 Pig

Transmissible gastroenteritis: This is a coronavirus infection causing vomiting and diarrhoea in pigs of any age. The virus destroys epithelial villi in the jejunoileum, result­ing in malabsorption and dehydration.

5.3.5 Dog

Canine parvovirus: Canine parvovirus infection is a highly contagious and virulent infection of dogs and some non-domestic mammals. Two forms of the disease are rec­ognised - intestinal and cardiac.

Haemorrhagic gastroenteritis: This condition is characterised by an acute onset of haemorrhagic diarrhoea and vomiting. Small and toy breed dogs under 5 years of age seem especially susceptible. The cause is unknown, but a Clostridial infection has been suspected. The principal lesion is a haemorrhagic inflammation and necrosis of the intestines. Involvement of the stomach is minimal, and the lesion affects the large intes­tine more than the small one.

Foreign body: A variety of foreign bodies may be swallowed by dogs and cats. Common items are toys, bones, socks and fishhooks. The clinical signs relate to intesti­nal obstruction, i.e. abdominal discomfort, vomiting, loss of appetite. Palpation and radiography may lead to a prompt diagnosis.

Malabsorption: The pancreatic enzymes convert many of the nutrients presented at the intestinal mucosa into simpler compounds that are able to cross the enterocyte bar­rier and enter the bloodstream on their way to the liver. However, if the pancreatic enzymes are deficient, this process of aided absorption is severely retarded. This situa­tion is labelled exocrine pancreatic insufficiency (EPI) and occurs in dogs. Malabsorption can also be a result of small intestinal bacterial overgrowth (SIBO). German Shepherd Dogs are the breed most commonly affected by these conditions, which may occur sin­gly or together.

Intussception: A variety of causes can be responsible for a telescoping of the intes­tine, e.g. intestinal parasites, bacterial or viral infections, foreign bodies, intestinal tumours and dietary changes. Usually, the intussception involves peristaltic entry of a proximal segment into a static distal segment. Intussceptions occur most commonly in the jejunum and in puppies. Diagnosis is by palpation or radiography in a dog or cat with sudden onset of vomiting, diarrhoea, abdominal pain and straining to defaecate. Any delay in treatment rapidly results in haemostasis and tissue necrosis. Early surgical manipulation may be successful, but resection and anastomosis may be necessary.