Abbey Veterinary Services

DIAGNOSTIC HISTOPATHOLOGY AND CYTOLOGY

CASE OF INTEREST

A case of haemorrhagic canine gastroenteritis in a Boxer dog.

By Richard Fox, Veterinary Pathologist

Case donated by Lucy Genovese, Veterinary Pathologist.

A six year old Boxer dog was presented due to sudden collapse with a marked tachyarrythmia, mucous membrane pallor with a mucous membrane capillary refill time of 2 seconds. The dog died within a short time after presentation shortly after intravenous catheterisation.

A necropsy was performed soon after death. Bloodstained, foul-smelling but fluid faeces were found on initial examination. On opening the stomach there was an area of gastric mucosal haemorrhage. Within the small and large intestine (primarily in the duodenum and jejunum) a thick fibrinonecrotic and haemorrhagic exudate was found. Petecchial haemorrhages were found diffusely on the epicardium and within the myocardium. Sections of tissue were submitted for histopathological examination.

Histological examination of the tissues identified lesions limited to the small and large intestine and heart. In the colon there was focal to focally extensive necrosis of the superficial lamina propria. Haemorrhage was present and extended from the surface into the lamina propria, vessels were engorged and a number contained fibrin thrombi. Large numbers of bacteria covered denuded, partly necrotic surface of the mucosa. A Gram stain indicated these to be almost a pure population of Gram positive bacilli. Inflammatory infiltrates within the mucosa and submucosa were minimal (residual mononuclear cells). The deeper proprial tissue was intact. Some crypts contained a small amount of cellular debris. Vessels within the submucosa displayed moderate dilatation and congestion. There was milder vascular dilatation within the tunica muscularis.

Within the duodenum and ileum there was loss of villus architecture. The tips of the villi were necrotic and covered by a heavy mass of bacteria of similar appearance to that in the colon. Low numbers of neutrophils were present within the superficial necrotic tissue and occasional fibrin thrombi were evident within vessels. The degree of congestion and necrosis was less severe in the small intestinal samples.

Figure 1. Histological section of the large intestine displaying marked mucosal necrosis and lamina proprial haemorrhage and submucosal congestion. (x2.5 obj.). HE Stain.

Figure 2. Histological section of a groups of crypts displaying necrosis, haemorrhage and a basophilic line covering the necrotic mucosal surface (bacteria). (x5 obj.). HE Stain.

There were colonies of bacteria visible on the ulcerated surface but on staining with Gram moderate numbers of Gram positive cocoid intracellular and extracellular bacteria were observed.

Figure 3. Histological section of the the colonic mucosa covered in multiple Gram positive rod-shaped bacteria (x10 obj.). Gram Stain.

Sections of myocardium from the right ventricle identified a mild increase in subendocardial fibrous tissue. There is multifocal replacement of myofibres by fat. This varied from clusters of individual lipocytes to focally extensive areas of myocardial fat replacement. In the right atrium changes were very similar. Mild epicardial fibrosis was present with a mild accumualtion of mononuclear inflammatory cells, including some lymphocytes and macrophages, occasionally present around blood vessels and focally mildly extending into muscle.

The severe haemorrhagic and necrotising enterocolitis, which was most severe in the colon was consistent with haemorrhagic canine gastroenteritis which is a sporadic per-acute haemorrhagic disease. The exact pathogenesis is not well understood but Clostridium Perfringens type A (some of them enterotoxin producing) has been identified in some cases. The disease is per-acute and dogs are often found dead. All of the intestine appears lined by a very heavy, almost pure growth of large bacilli and, given the well preserved nature of the samples and lack of evidence of autolysis, the presence of these organisms was regarded as clinically significant although culture and typing would be required for their definitive identification.

Microscopically this case is typical in that necrohaemorrhagic lesions are present within the gastrointestinal mucosa, which extends from the lumenal surface into the lamina propria. The bacteria, Clostridia, covers the necrotic tissue but does not invade it. Recurrent diarrhoea, sometimes bloody, has been associated with entero-toxin secreting type A strains. Multiple serotypes of Clostridia have been associated with nosocomial, usually non-fatal, cases of diarrhoea in dogs.

The cardiac lesion present in this dog was deemed to be a cardiomyopathy. There was fatty replacement of muscle within the atria and the right ventricle. There is a variant of dilated cardiomyopathy described in Boxer dogs, termed arrhythmogenic right ventricular cardiomyopathy. Right ventricular dilatation or aneurysms are common. Arrhythmias are also common and the condition is associated with sudden death. Mild non suppurative myocarditis has also been reported with this syndrome and was present to a very limited extent. Shock and electrolyte abnormalities associated with the severe haemorrhagic intestinal lesion likely contributed to arrhythmia and cardiac failure in this dog.

References:

1. Brown, CC. et al: Alimentary system. In: Pathology of Domestic Animals, eds. Jubb KVF, Kennedy PC, Palmer N, 5th ed., vol. 3, pp. 215-215. Elsevier Ltd, New York. 2007.

2. Sasaki J, Goryo M, Asahina M, Makara M, Shishido S, Okada K. Hemorrhagic enteritis associated with Clostridium perfringens type A in a dog. J Vet Med Sci. 1999 Feb;61(2):175-7.

3. Weese JS, Greenwood SJ, Staempfli HR. Recurrent diarrhea associated with enterotoxigenic Clostridium perfringens in 2 dogs. Can Vet J. 2001 Apr;42(4):292-4.