Group A rotavirus (RVA) is a major cause of acute gastroenteritis in infants and young children worldwide. This study aims to clarify the distribution of G/P types and genetic characteristics of RVAs circulating in Thailand. Between January 2014 and September 2016, 1867 stool specimens were collected from children and adults with acute gastroenteritis in six provinces in Thailand. RVAs were detected in 514/1867 (27.5%) stool specimens. G1P (44.7%) was the most predominant genotype, followed by G3P (33.7%), G2P (11.5%), G8P (7.0%), and G9P (1.3%). Unusual G3P (0.8%), G3P (0.4%), G4P (0.4%), and G10P (0.2%) were also detected at low frequencies. The predominant genotype, G1P (64.4%), in 2014 decreased to 6.1% in 2016. In contrast, the frequency of G3P markedly increased from 5.5% in 2014 to 65.3% in 2015 and 89.8% in 2016. On polyacrylamide gel electrophoresis, most (135/140; 96.4%) of the G3P strains exhibited a short RNA profile. Successful determination of the nucleotide sequences of the VP7 genes of 98 G3P strains with a short RNA profile showed that they are all equine-like G3P strains. On phylogenetic analysis of genome segments of two representative Thai equine-like G3P strains, it was noteworthy that they possessed distinct NSP4 genes, one bovine-like and the other human-like. Thus, we found that characteristic equine-like G3P strains with a short RNA electropherotype are becoming highly prevalent in children and adults in Thailand.
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