Epidemiological study of bovine norovirus infection by RT-PCR and a VLP-based antibody ELISA

Noroviruses, belonging to the family Caliciviridae, have been identified in human beings and in several animal species including cattle. The distribution of bovine norovirus infections was investigated by both RT-PCR to detect norovirus genomes and a virus-like particles-based ELISA to detect genotype 2 bovine norovirus antibodies. During a 1-year systematic study, a virus prevalence of 7.5% (CI 95%: [3.7; 13.4%]) (10 out of 133 samples) was found in stool samples from diarrhoeic calves screened by RT-PCR. Nucleotide sequencing performed on the polymerase region classified all the norovirus amplicons in the bovine norovirus genotype 2. Rather surprisingly, some rotavirus sequences were also detected. On the basis of the polymerase region, genotype 1 bovine norovirus was not identified. Other enteropathogens were found in all samples. By ELISA, a genotype 2 seroprevalence of 93.2% (CI 95%: [90.4; 95.3%]) was found from calves and adult cattle. Antibody levels against genotype 2 bovine noroviruses rose in the first 6 months of life and were maintained in adults. Together the results of virus prevalence and seroprevalence studies suggest that bovine norovirus infection occurs early in life and that re-infection with serologically related bovine noroviruses strains could occur in adult cattle as reported for rotaviruses. The antibody rise against genotype 2 bovine noroviruses in the adult cattle also suggests a short lived and/or strain specific immunity as already shown in human noroviruses. Genotype 2 bovine noroviruses are endemic in the region investigated.