Epidemiology of Norwalk-like virus infections in cattle in The Netherlands

"Norwalk-like viruses" (NLVs) are the most common cause of acute non-bacterial gastroenteritis in humans. Cattle may be a reservoir of NLVs although never bovine NLVs have been found in humans. To gain more insight into the epidemiology of NLV, infections in cattle in The Netherlands were studied. Individual faecal samples from a large dairy herd and 243 pooled samples from veal calf farms were analysed for NLV by RT-PCR. Calves under 3 months of age in the dairy herd were sampled three to five times with 3-week intervals, whereas dairy cattle were sampled twice with a 2-month interval. In 31.6% (77/243) of the veal calf farm samples and in 4.2% (13/312) of the individual dairy cattle samples NLV was detected. The mean age of virus positive dairy cattle was 2.5 months. The highest numbers of NLV positive veal calf farms in The Netherlands were found in the regions with the highest number of veal calf farms. NLV infected veal calf farms were detected in every month throughout the study period. Cattle appeared to be hosts of NLVs, and virus shedding was weakly associated with diarrhoea. Complete ORF2 sequences were obtained from two calf NLVs and phylogenetic analyses suggested that these strains belong to a distinct cluster (GGIII/2) in between GGI and GGII NLVs of humans. Overall, genetic variation between strains as determined by sequence analysis of the P1/P2 capsid region was limited to 14.6%. Our data shows that NLV is endemic in the cattle population in The Netherlands and genetically distinct from NLVs in humans.