Whole-genome classification of rotavirus C and genetic diversity of porcine strains in the USA

Rotavirus C (RVC) is associated with acute diarrhoea in both children and young animals. Because of its frequent occurrence, additional sequences have recently been generated. In this study, we sequenced 21 complete genomes from porcine diarrhoea samples and analysed them together with all available reference sequences collected from the GenBank database [National Center for Biotechnology Information (NCBI)]. Based on phylogenetic analysis and genetic distance calculation, the number of each segment was identified as 31G, 26P, 13I, 5R, 5C, 5M, 12A, 10 N, 9T, 8E and 4 H for genotypes encoding VP7, VP4, VP6, VP1, VP2, VP3 and NSP1, NSP2, NSP3, NSP4 and NSP5, respectively. From the analysis, genotypes G19–G31, P[22]–P[26], R5, A9–A12, N9–N10, T7–T9 and E6–E8 were defined as newly identified genotypes, and genotype C6 was combined with C5, and M6 was combined with M1, due to their closely related nature. Estimated with the identity frequency ratio between the intergenotype and intragenotype, the nucleotide identity cutoff values for different genotypes were determined as 85, 85, 86, 84, 83, 84, 82, 87, 84, 81 and 79 % for VP7, VP4, VP6, VP1, VP2, VP3, NSP1, NSP2, NSP3, NSP4 and NSP5, respectively. Genotyping of the 49 US strains indicated possible segment reassortment in 9 of the 11 segments, with the exceptions being VP1 and NSP5, and the most prevalent genotypes for each segment genes in the USA were G6/G5/G21/G9-P5/P4-I6/I5-R1-C5-M1-A8-N1/N10-T1-E1-H1. Our study updated the genotypes of RVC strains and provided more evidence of RVC strain diversity that may be relevant to better understand genetic diversity, and the distribution and evolution of RVC strains.