Electron microscopic studies of bovine viral diarrhea virus in tissues of diseased calves and in cell cultures.

Pathomorphological studies by electron microscopy (EM) were carried out on the intestines and lymphoid tissues, the buffy coat cells and cultured lymphocytes from calves suffering from mucosal disease (MD). This led to the detection of particles, 45--55 nm in diameter, within characteristic vesicular structures. As these findings coincided with the isolation of bovine viral diarrhea virus (BVDV) from the same tissues and demonstration of BVDV-antigen by immunocytochemical techniques in corresponding samples, the particles were tentatively identified as the BVDV. A detailed study of in vitro infected bovine cell cultures corroborated this supposition and contributed to a conjectural evaluation of the viral morphogenesis. It revealed a difference from the morphogenesis of most other togaviruses, as the presumed virions were assembled within smooth-membraned vesicles, formed during the infection. Thus, in the material examined, a budding process was not involved in the development of BVDV.