Histological comparison of malignant epithelioid mesothelioma in young and adult cattle.

The histology and immunohistochemistry of pleomorphic and conventional epithelioid mesotheliomas were examined. The former was detected in two young calves aged 2 and 4 months and was characterized by pleomorphic and atypical cells with decreased expression of cytokeratin 7 (CK7). In contrast, the latter was found in a 31-month-old heifer, consisting of tumor cells uniform in size and shape with CK7 expression in nearly all cells. Production of collagen by tumor cells was demonstrated in both histological types, and was considered to be characteristic of bovine epithelioid mesothelioma. Pleomorphic mesothelioma is far more pleomorphic and mitotically active than conventional mesothelioma, and its normal counterpart may be immature mesothelial cells with high proliferation potential, which exist in fetal life and early calfhood.

Eosinophilic granuloma with Splendore-Hoeppli material caused by Mannheimia granulomatis in a calf.

A large subcutaneous mass, formed on the left lower jaw of a 4-month-old Japanese Black male calf, was partially excised for histological and bacteriological examinations. Antibiotic treatment resulted in a good prognosis. Bacteria isolated from the excised material were characterized by weak hemolysis and positive reactions for catalase and oxidase, and were 99% identical to Mannheimia granulomatis strains. The presence of the leukotoxin gene product was demonstrated by polymerase chain reaction amplification. Histological examination showed that the excised material was composed of dense fibrous connective tissue with sparsely distributed eosinophilic granulomas or abscesses. These foci frequently contained Splendore-Hoeppli material with rod-shaped Gram-negative bacteria. Except for the absence of lymphangitis and the presence of basophils and mast cells, the histology of this lesion resembled that of lechiguana associated with coinfection of M. granulomatis and Dermatobia hominis. Leukotoxin was demonstrated by immunohistochemistry within Splendore-Hoeppli material and was judged to be responsible for its formation.