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Although reassortment is one of the most important characteristics of group A rotavirus (RVA) evolution, the host range restriction and/or virulence of reassortant RVAs remain largely unknown. The porcine 174-1 strain isolated from a diarrheic piglet was identified as a reassortant strain, harboring the same genotype constellation as the previously characterized bovine strain KJ56-1. Owing to its same genotype constellation, the pathogenicity of the porcine strain 174-1 in piglets and calves was examined for comparison with that of the bovine reassortant KJ56-1 strain, whose pathogenicity has already been demonstrated in piglets and calves. The porcine 174-1 strain induced diarrhea and histopathological changes in the small intestine of piglets and calves, whereas KJ56-1 had been reported to be virulent only in piglets, but not in calves. Therefore, full genomic sequences of 174-1 and KJ56-1 strains were analyzed to determine whether specific mutations might be associated with clinical and pathological phenotypes. Sequence alignment between the 174-1 and KJ56-1 strains detected one nucleotide substitution at the 3′ untranslated region of the NSP3 gene and 16 amino acid substitutions at the VP7, VP4, VP1, VP3, NSP1 and NSP4 genes. These mutations may be critical molecular determinants for different virulence and/or pathogenicity of each strain. This study presents new insights into the host range restriction and/or virulence of RVAs. [ABSTRACT FROM AUTHOR]