Pathogenesis of bovine viral diarrhoea-mucosal disease: distribution and significance of BVDV antigen in diseased calves.

The distribution of bovine viral diarrhoea virus (BVDV) antigen in tissues of animals with acute and chronic bovine viral diarrhoea-mucosal disease (BVD-MD) was examined using improved indirect immunofluorescence and indirect immunoperoxidase staining methods on cryostat and paraffin wax tissue sections. In lymphoid tissues the antigen was principally located in cells belonging to the mononuclear located in cells belonging to the mononuclear phagocyte system and in other cells with antigen-retaining capacity. The distribution of the infected cells within a particular organ varied with the clinical stage. In the non-lymphoid organs the antigen was detected in cells of the mononuclear phagocyte system as well as in epithelial cells. An apparent time lag between initial antigen-detection and progression of pathological manifestations was noticed in the intestinal mucosa and in the keratinized epithelia of the upper digestive system and in the skin. Only limited involvement of blood vessels was observed in the tissues investigated. In the light of the mononuclear phagocyte system being an apparent common denominator for all the different tissues involved in the morphological alterations which characterise BVD-MD, a possible pathogenesis of BVDV-MD is discussed.