Isolation of bovine viral diarrhoea viruses from bison

Abstract

intranasally with 2 x 107 TCID50. The calves were monitored daily for signs of disease, and blood samples and nasal and rectal swabs were collected on the day of inoculation and two, four, seven, nine, 11, 14, 17, 21, 24 and 28 days later. All procedures complied with the guidelines of the Canadian Council on Animal Care. Virus isolation was performed as described by Tessaro and others (1999). Two of the three calves developed fever (40·5 and 42·0°C), but none showed any other signs of disease. Virus was only isolated from serum and/or leucocytes four and seven days after inoculation. All three animals showed a decrease in total leucocyte counts of 50 per cent or more by day 7, and had seroconverted to BVDV at day 11, as determined by a serum neutralisation assay (Deregt and others 1992). Thus, although the isolate could infect cattle, it appeared to be innocuous, at least for calves of this age group. Both of the bison isolates were typed as BVDV-1 using a multiplex PCR that distinguishes between BVDV-1 and BVDV-2 strains (Gilbert and others 1999). This PCR uses primers to amplify sequences of the NS5B polymerase gene. Since this gene has not been used for phylogenetic analysis, as have the Npro and E2 genes, the entire E2 gene of each isolate was sequenced by the methods described by Deregt and others (1998) (Fig 1). The phylogenetic relationships between the E2 genes of pestiviruses representing all five recognised species were determined using the distance matrix programs PRODIST and FITCH (PHYLIP). Bootstrap resampling of the phylogenetic trees was carried out to test the robustness of the observed clades. The phylogenetic relationships of the two bison isolates to other pestiviruses are shown in Fig 2. Both bison isolates clustered in the species BVDV-1, with isolate V1127 in the BVDV Isolation of bovine viral diarrhoea viruses from bison