[Pathogenicity of noncytophatic isolates of bovine viral diarrhea virus in experimentally infected seronegative calves].

The results of experimental infection of seronegative calves with three non-cytopathogenic (NCP) isolates of BVDV isolated from cattle with different clinical manifestations of the disease belonging to genotype 1 (subgenotype 1a, 1b and 1d) are presented. All tested isolates showed the virulence for seronegative calves 4 to 6 months of age. Belonging to biotype did not correlate with the ability of the virus to infect the lymphoid tissues and to induce leukopenia. All isolates of the virus led to "transiting" leukopenia (up to 2880-3800 kl/mm3) for 8-10 days after infection. Isolate cluster 1d was more virulent and caused the development of a mild respiratory syndrome and short-term diarrhea. The virulence was "strain-dependent".