The pathomorphology of malignant catarrhal fever. II. Multisystemic epithelial lesions.

Epithelia from 18 Holstein-Fresian calves with experimentally induced malignant catarrhal fever and two calves with naturally occurring disease had severe destructive inflammatory epithelial lesions. Calves were necropsied at early, mid and late clinical stages. Multifocal, degenerative and necrotic epithelial lesions were associated with lymphoid cells. Ultrastructurally, numerous lymphocytes, lymphoblasts and macrophages were accumulated between epithelial cells and in lamina propria, vessels and perivascular tissues. Epithelial cells in such lesions had variably severe degenerative changes or were necrotic but there was no proliferative response. Lesions were widespread in all calves and affected oral, ocular, gastrointestinal, ductal, urinary tract, choroid plexus and other epithelial tissues. Calves killed in late clinical stages had more severe lesions than those killed early. The predominantly lymphocytic, invasive-destructive pattern seen in tissues of cattle with malignant catarrhal fever was similar to that seen in such conditions as contact hypersensitivity and graft versus host disease. Viral structures were not seen.