Electron microscopy of bovine virus diarrhoea virus

Bovine virus diarrhoea virus (BVDV) has been (tentatively) identified by electron microscopy in purified virus preparations, in infected cell cultures and in tissues and cells from infected animals. These studies have revealed a spherical membrane-bound particle with a diameter of 40-60 nm. The membrane is smooth, bilaminar and surrounds a dense or semi-dense core of 20-25 nm. The core particle may be isometric or hexagonal. In studies of the morphogenesis of BVDV in infected cell cultures, it was found that assembly and maturation of the viral particles occur via a condensation process within membrane-bound vesicular organelles, in which the virions subsequently accumulate. Release of the virus occurs when the cell finally lyses and/or via exocytosis. Thus, both with regard to morphogenesis and to morphology, BVDV bears close resemblance to the Flaviviridae.