This is a chronic inflammatory condition of the digestive tract which may involve only the small intestine or may also involve the stomach or large intestine (). There appear to be more cases reported in German Shepherd dogs although other breeds may also be affected. The aetiology is thought to be an allergic reaction to food components () or internal parasites such as Toxocara canis (). It has been reported in both dogs and cats although it is not as common as lymphocytic—plasmacytic enteritis. In cats the eosinophil infiltration may be more extensive and involve tissues outwith the digestive tract.
It is thought the eosinophils are attracted to the intestine by a chemotactic factor produced from intestinal mast cells which suggest a type 1 hyper-sensitivity reaction has occurred. However chemotactic factor is also released by T lymphocytes and complement so there may be an Arthus reaction or delayed cell-mediated hypersensitivity involved ()
The clinical signs depend on the severity of the condition in the individual dog or cat. In dogs many cases are mild leading to chronic diarrhoea and variable weight loss. In severe cases hypoproteinaemia develops due to the loss of plasma proteins into the intestine, resulting in subcutaneous oedema, ascites and hydrothorax. In these cases weight-loss and diarrhoea are severe. If the large intestine is involved, fresh blood and tenesmus are often observed. Where the stomach is involved vomiting will also be a feature and may occasionally contain blood. Although the appetite is initially normal this will change and anorexia will develop. Cats are most frequently involved in middle age and exhibit vomiting and diarrhoea often with blood present and are almost always anorexic. Hepatomegaly, splenomegaly and lymphadenopathy may also be seen in cats ().
Diagnosis may be confirmed by examination of whole blood for a persistent eosinophilia together with examination for evidence of hypoproteinaemia. A definitive diagnosis requires a laparotomy to collect small intestinal biopsy samples. Histological examination will reveal heavy infiltration of eosinophils throughout the wall of the intestine and involve the mesenteric lymph nodes (). Careful examination for evidence of parasitic involvement should also be carried out, particularly for signs of Toxocara canis larva.
Eosinophilic enteritis: Treatment
As with lymphocytic—plasmacytic enteritis, there appears to be an immune basis to the problem. Therefore treatment usually involves the use of prednisolone at 2 to 4mg/kg/day for at least 4 weeks, followed by a period of reduced dosage. The addition of azathioprine (Imuran; Calmic Medical Division) may be required in severe cases. Tylosin has been shown to be effective in treating the condition (). If evidence of parasitic involvement is present then an anthelmintic which is effective against adults and larvae should be included. It is advisable to consider changing the diet to a hypoallergenic diet such as Waltham selected protein diet or Hills d/d diet. Where the severe form of the condition is present, the prognosis must be guarded, but in mild forms the prognosis is reasonable, especially if the dietary change is maintained after the initial treatment has been completed. Treatment of cats is similar but likely to be less successful.