Bovine viral diarrhea virus (BVDV) is an economically important pathogen of cattle throughout the world, causing a wide range of clinical syndromes. Virion is spherical, 40-70 nm in diameter, with an envelope tightly applied to a spherical nucleocapsid 25-35 nm in diameter with icosahedral symmetry (figure 1 and 2) (Matthews, 1979) . It is presently included in the Togavlridae family, genus Pneumovirus but Collett et al. (1988) have proposed to group this genus in the Flaviviridae family. In the present study, two strains of BVDV were compared by electron microcospy ultrathin sections: one cytopathogenic, NADL strain, and the other non-cytopathogenic, NY-1 strain. These were Inoculated on Madney-Darby Bovine Kidney (MDBK) cells to a multiplicity of infection (m.o.i) between 3,0 and 5,0. Control and virus infected cells were fixed with glutaraldehyde (2,5% in cacodylate buffer) at 24 , 48, 72 and 96 h following incubation at 37°C. Cells were postfixed with osmium tetroxide and embedded in Vestopal.The NADL-CP strain infected cells showed vacuolization of the endoplasmic reticulum, ribosomal activity in the cytoplasm and appearance of virus particles 48h after infection (figure 3). At 72h, an expensive vacuolization was apparent (figure 4). Maximum viral production was seen 96 h after infection (figure 5). From 24 to 72 h post infection, the NY-l-NCP strain of BVD infected cells showed normal vacuolization like in control cells. They produced weak vacuolization with few particles, not apparent before 96h after infection (figure 6). Viral particles of 45-50 nm in endoplasmic reticulum vacuoles were in general homogenous in size while those in smooth membranes, probably of cellular origin, heterogenous in size.
Detection of Bovine Viral Diarrhea Virus in some Vaccines, Sera and Cell Cultures
