Multiple outbreaks of severe acute BVDV in North America occurring between 1993 and 1995 linked to the same BVDV2 strain

The first reported outbreak of bovine viral diarrhea (BVD) in 1946 described a transmissible acute disease characterized by severe leukopenia, high fever, gastrointestinal erosions and hemorrhages. However, in the ensuing years, the most commonly observed acute form of BVD was clinically mild. There was limited viral shed and spread following these acute infections. This led to the assumptions that acute infections with BVD viruses (BVDV) were clinically unimportant, spread of the virus within a group was always due to the presence of a persistently infected animal and transmission between healthy immunocompetent cattle was insignificant. These assumptions were challenged when outbreaks of severe acute BVDV were observed in North America starting in the late 1980s. This study demonstrates that widespread outbreaks of severe acute BVD observed in 1993 in North America can be traced to a single strain of BVDV that apparently spread explosively following acute infection. These findings are notable in that they draw into question management of acute BVD infection, design of studies examining virulence and nomenclature used to identify strains for GenBank submission.