IDENTIFICATION OF A NEW GROUP OF BOVINE VIRAL DIARRHEA VIRUS-STRAINS ASSOCIATED WITH SEVERE OUTBREAKS AND HIGH MORTALITIES

New BVDV strains associated with very high mortalities, which killed a bout 25% of the veal calves in Quebec in 1993, have been isolated. In this study, characterization of the last two-thirds of the 5' untransl ated region (5'UTR) of their genomes and virus neutralization experime nts with polyvalent antisera raised in different animals both demonstr ated that these strains formed a distinct group. Despite a difference of about 25% in the 5'UTR sequence with that of the classical strains, these 5'UTRs maintained the same secondary structure albeit with a hi gher stability. Serological crossreactivity between the classical and new BVDV strains was relatively low and suggest that new strains shoul d also be included to obtain efficient BVDV vaccines. Based upon the d istinct characteristics of these new BVDV strains, we propose to divid e BVDV into two groups. Group I comprises the classical BVDV isolates including commonly used laboratory and vaccine strains, and group II c omprises the newly described BVDV strains and those associated with th rombocytopenia and hemorrhaging. (C) 1994 Academic Press, Inc.