COMPARISON OF BOVINE CORONAVIRUS ISOLATES ASSOCIATED WITH NEONATAL CALF DIARRHEA AND WINTER DYSENTERY IN ADULT DAIRY-CATTLE IN QUEBEC

Cytopathic coronaviruses were isolated in HRT-18 cells from bloody faecal samples collected from cows in Quebec dairy herds having experienced typical outbreaks of winter dysentery (WD). The formation of polykaryons in the infected cell cultures was found to be dependent on the presence of trypsin in the medium. The WD isolates differed from the prototype Mebus strain of bovine enteropathogenic coronavirus (BCV.Meb) in respect to haemagglutination inhibition (HI), haemagglutination patterns at 4 degrees C and 37 degrees C, and receptor destroying enzyme activity with rat erythrocytes. Other held strains of BCV associated with outbreaks of neonatal calf diarrhoea (NCD) also differed from the BCV.Meb strain by demonstrating differences in HI. In all cases, no differences were detected by virus neutralization and Western immunoblotting. Analysis and comparison of the nucleotide and deduced amino acid sequences of the PCR-amplified haemagglutinin esterase (HE) genes of one representative WD strain (BCQ.2590) and two highly cytopathic NCD strains (BCQ.3 and BCQ.571) revealed high degrees of similarities (nt and aa sequence homologies > 98%) with the BCV.Meb strain. The putative esterase active site FGDS was conserved among these four BCV strains, indicating that this domain is probably not a determinant for BCV virulence. Six amino acid substitutions occurred between the HE glycoproteins of BCV.Meb and BCQ.2590 strains; two proline substitutions occurred respectively in the signal peptide (at aa 5) and near the sequences of the putative esterase domain (at aa 53).