September 2012

Case A

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Coughing in feedlot dairy calves.

Example histopathological description

The slide contains a 2 x 1 cm section of lung. There is very little aerated lung present. Most lobules are disrupted and effaced by multiple foci of inflammation and necrosis. Many bronchi and bronchioles are dilated and plugged by granulocytes, necrotic debris and desquamated epithelial cells (bronchiolitis obliterans). Occasional intraluminal fibrous polyps are present and airways are surrounded by variable amounts of fibrosis and some are lined by plump hyperplastic epithelium which is multilayered in places. Inflammation (fibrin, oedema, neutrophils) and fibrosis extend multifocally to adjacent interlobular interstitial tissues and to the pleura. Multiple foci throughout the section have a central core of lytic necrosis surrounded by a zone of neutrophils, then a layer of macrophages with fewer lymphocytes and plasma cells and an outer zone of fibroblasts (abscesses/granulomas).  Smudgy basophilic areas in the necrotic cores may be bacterial colonies. The remaining alveolar epithelium often shows areas of type 2 pneumocyte hyperplasia. Intact alveoli contain macrophages, neutrophils, eosinophils and lymphocytes.

Morphological diagnosis

Pneumonia, bronchointerstitial, severe, diffuse, subacute to chronic with multifocal abscessation, bronchiectasis and epithelial hyperplasia.

Differential diagnosis

Bovine respiratory disease complex can involve a variable number of viruses such as parainfluenza virus 3, infectious bovine rhinotracheitis virus, bovine respiratory syncitial virus and bovine pestivirus, together with a range of bacteria including: Mycoplasma bovisMannheimia haemolytica, Pasteurella multocida,Histophilus somni and Truperella pyogenes.

Case B

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Illthirift and scouring in grower pigs.

Example histopathological description

The specimen is an almost complete cross-section of colon with some artefacts of autolysis. There is extensive epithelial hyperaemia, erosion and multiple deep ulcers with a mixed bacterial population attached to the luminal surface. The ulcers are sharply demarcated, contain a bed of neutrophils, necrotic debris and fibrin and extend into the superficial submucosa where fibrinocellular thrombi in nearby vessels are present. Adjacent tissues are expanded by prominent infiltrates of proteinaceous fluid, fibrin, neutrophils, lymphocytes, plasma cells, macrophages, dilated lymphatics and activated fibroblasts. The remaining mucosa shows dilation, attenuation and loss of mucosal glands, mild enterocyte necrosis and hyperplasia with prominent mitotic figures and mucin accumulation. Multifocally, in crypts and embedded in the mucosa, are large (35-70 µm diameter) round organisms with a thin wall, multiple eosinophilic organelles and a large dark basophilic nucleus (consistent with Ballantidium coli).

Morphological Diagnosis

Colitis, ulcerative, subacute, severe, multifocal with vascular thrombosis.

Differential Diagnoses

Enteric salmonellosis is the primary differential diagnosis.  Others to consider are swine dysentery,Trichuris suis infestation and classical swine fever.  Ballantidium coli infection is considered an incidental finding.