Prevalence of Bovine Norovirus and Nebovirus and Risk Factors of Infection in Swedish Dairy Herds

Enteritis is the major cause of mortality in neonatal calves. Diagnostic work to detect the pathogens involved and identification of risk factors for such infections are imperative to improve calf health. Bovine norovirus (BNoV) and nebovirus prevalence was investigated using RT-PCR in 50 dairy herds in five geographic regions of Sweden. BNoV and nebovirus were found to be common infections in young dairy calves. BNoV was detected in 20% of 250 calves in 48% of the herds. Nebovirus was detected in 5% of the calves in 16% of the herds. Both infections were present in three herds (6%). BNoV-infected calves were younger (median age 7 days) than nebovirus-infected calves (median age 21 days). These infections were not detected in adult cows and young stock over 6 months of age tested in selected herds. Risk factors identified for BNoV infection were a high number of preweaned calves present at the time of sampling, colostrum uptake by suckling the dam only, calf kept in a single pen, and geographic location of herd, while no risk factors for nebovirus infection were identified in the multivariable analysis. Univariable analysis suggested risk factors for nebovirus infection to be geographic location and early separation from the dam.