DETECTION OF BOVINE TOROVIRUS IN FECAL SPECIMENS OF CALVES WITH DIARRHEA FROM ONTARIO FARMS

Breda virus (BRV), a member of the genus Torovirus, is an established etiological agent of disease in cattle. BRV isolates have been detecte d in the stools of neonatal calves with diarrhea in both Iowa and Ohio and in several areas of Europe. However, this virus has been reported only once in Canada. Therefore, a study was performed to determine th e extent to which bo tine torovirus is present in calves with diarrhea from farms in southern Ontario. A total of 118 fecal samples from sym ptomatic calves and 43 control specimens from asymptomatic calves were examined by electron microscopy (EM) and reverse transcription-PCR (R T-PCR) for the presence of torovirus. Torovirus RNA was detected in 43 of the 118 diarrheic samples (36.4%) by RT-PCR with primers designed in the conserved 3' end of the torovirus genome. By EM, torovirus part icles were observed in 37 of the 118 specimens (31.4%). All but one of these samples were also positive by RT-PCR. The incidence of toroviru s in the asymptomatic control specimens by RT-PCR was only 11.6%. To e stablish the identity of the particles observed in the diarrheic speci mens, five of the amplicons from samples positive by both RT-PCR and E M were cloned and sequenced. Nucleotide sequence analysis revealed tha t the bovine torovirus found in southern Ontario manifests between 96 and 97% sequence identity to the BRV type 1 strain found in Iowa. This study shows that bovine torovirus is a common virus in the fecal spec imens of calves with diarrhea from farms in southern Ontario and thus may be an important pathogen of cattle.