Multiple outbreaks of severe acute BVDV in North America occurring between 1993 and 1995 linked to the same BVDV2 strain Julia F. Ridpath a, * , John D. Neill a , Stefan Vilcek b , Edward J. Dubovi c , Suzanne Carman d a Virus and Prion Diseases of Livestock Research Unit, National Animal Disease Center, USDA, Agricultural Research Service, 2300 Dayton Avenue, P.O. Box 70, Ames, IA 50010, USA b Department of Infectious Diseases, University of Veterinary Medicine, Komenskeho, Slovakia c Molecular Diagnostic Laboratory, AHDL, Department of Population Medicine and Diagnostic Science, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA d Animal Health Laboratory, Laboratory Services Division, University of Guelph, Guelph, Ont., Canada Abstract 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. Published by Elsevier B.V. Keywords: Bovine viral diarrhea virus; BVDV2; High virulence BVDV strains; Severe acute BVD 1. Introduction When first described by Cornell University researchers in 1946 (Olafson et al., 1946) bovine viral diarrhea (BVD) was characterized as an acute www.elsevier.com/locate/vetmic Veterinary Microbiology 114 (2006) 196–204 * Corresponding author. Tel.: +1 515 663 7586; fax: +1 515 663 7458. E-mail address: jridpath@nadc.ars.usda.gov (J.F. Ridpath). 0378-1135/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.vetmic.2005.11.059