Retrospective (2016-2020) and cross-sectional molecular study of rotavirus species A field strains circulating in diarrheic dairy calves in Brazil.

Diarrhea is one of the main causes of death in calves worldwide, and rotavirus species A (RVA) is a significant etiological agent. This study aimed to determine the G (VP7 gene) and P (VP4 gene) genotype combinations in a collection of RVA-positive diarrheic fecal samples from dairy calves up to 30 days old. Between 2016 and 2020, 828 fecal samples from 118 dairy cattle herds were tested for rotavirus, with 154 (18.6 %) samples from 56 (47.5 %) herds positive for RVA. One RVA field strain per positive herd was selected for genotyping. To determine the genotypes, VP7 and VP4 genes were partially amplified by RT-PCR. The amplicons were purified, quantified, and sequenced. The genotype combinations found in 56 RVA-positive fecal samples were G6P[5] (n = 32, 57.1 %), G6P[11] (n = 20, 35.7 %), G10P[11] (n = 2, 3.6 %), and G10P[5] (n = 2, 3.6 %). Notably, the G10P[5] combination was first detected in Brazil. In addition, the RVA lineages P[5]-I, P[5]-III, and P[11]-VI had not yet been described in calves of Brazilian cattle herds. This study revealed a higher diversity of genotypes and P genotype lineages compared to previous studies in Brazil, highlighting the importance of monitoring RVA molecular characteristics to track viral evolution and mitigate animal health risks.