ABSTRACT. Seven of 92 lactating Holstein cows on a dairy farm developed urticaria with alopecia and decreased milk production, and three of the seven died over the course of 7 to 18 days. Pathologic examination of the three cows, including the two dead and one euthanized cow, revealed that the skin, liver, spleen, kidneys, heart, salivary glands, pancreas, adrenal glands, mammary glands, lymph nodes, and trigeminal ganglia had lymphocytic to lymphogranulomatous inflammation. Inflammation predominated by lymphocytic infiltration was prominent in the heart, pancreas, mammary glands, adrenal gland, and trigeminal ganglia. Severe granulomatous inflammation with multinucleated giant cells was present in the spleen and kidneys. These lesions and their distributions were most similar to those seen in suspected cases of citrus pulp toxicosis and hairy vetch toxicosis. The outbreak of this disease resolved with the elimination of Citrus pulp from the feed. Immunohistochemical detection of lymphocytes and macrophage markers confirmed dramatic hyperplasia of CD3-positive T lymphocytes in these lesions. This strongly suggested that a type 4 hypersensitivity reaction played a role in the development of the lesions.

A Japanese black feedlot steer suddenly died after exhibiting astasia and cramping of the extremities. Necropsy of the animal revealed that the right kidney was enlarged and pale with severe nephrolithiasis. The urinary bladder displayed mucosal hemorrhage. Upon bacteriological investigation, Proteus mirabilis was isolated from the liver, spleen, right kidney, lungs and urine. Histopathological examination revealed necrotizing suppurative nephritis with the presence of numerous gram-negative bacilli and fibrinous suppurative cystitis with no bacilli. Immunohistochemical analysis revealed that the bacteria and cytoplasm of the macrophages stained positively with P. mirabilis antiserum. Electron microscopy revealed the presence of numerous bacteria in the renal tubules. To our knowledge, this is the first report describing the histopathological aspects of nephritis caused by P. mirabilis in cattle.

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