Cross-sectional study of the G and P genotypes of rotavirus A field strains circulating in regularly vaccinated dairy cattle herds.

Neonatal diarrhea is the main cause of morbidity and mortality in calves up to 30 days old, and rotavirus A (RVA) is the main viral etiology. RVA vaccines are one of the main tools for diarrhea control in neonates. The aim of this cross-sectional study was to monitor by RT-PCR the G and P genotypes of RVA strains identified in dairy cattle herds regularly vaccinated with the RVA UK strain (G6P[5]). Of the 14 randomly selected herds, two were excluded because no calf was diagnosed with diarrhea on the day of fecal collection. Another six herds were also excluded from the study because all 20 diarrheic fecal samples evaluated were RT-PCR-negative. In the remaining six herds, 17 (25.4%) of the 67 diarrheic samples were RVA-positive. One G and P amplicon from each herd were selected for nucleotide sequencing. In the phylogenetic analysis, five RVA strains presented the G6P[11] genotype, and one presented the G10P[11] genotype. The G6 genotype present in all RVA field strains clustered into a distinct phylogenetic arrangement (lineage III) of the UK vaccine strain (lineage IV), characterizing the emergence of a phylogenetically distant G6 strain. In addition, we observed the emergence of strains with G10 and P[11] genotypes characterizing failure in heterologous immune protection. These results show the epidemiological importance of constant monitoring of RVA strains in vaccinated cattle herds and the low frequencies of diarrhea and diagnosis of RVA suggest that a regular vaccination program reduces the frequency and severity of RVA diarrhea in suckling calves.