Evolution of DS-1-like G8P[8] rotavirus A strains from Vietnamese children with acute gastroenteritis (2014-21): Adaptation and loss of animal rotavirus-derived genes during human-to-human spread.

Animal rotaviruses A (RVAs) are considered the source of emerging, novel RVA strains that have the potential to cause global spread in humans. A case in point was the emergence of G8 bovine RVA consisting of the P[8] VP4 gene and the DS-1-like backbone genes that appeared to have jumped into humans recently. However, it was not well documented what evolutionary changes occurred on the animal RVA-derived genes during circulation in humans. Rotavirus surveillance in Vietnam found that DS-1-like G8P[8] strains emerged in 2014, circulated in two prevalent waves, and disappeared in 2021. This surveillance provided us with a unique opportunity to investigate the whole process of evolutionary changes, which occurred in an animal RVA that had jumped the host species barrier. Of the 843 G8P[8] samples collected from children with acute diarrhoea in Vietnam between 2014 and 2021, fifty-eight strains were selected based on their distinctive electropherotypes of the genomic RNA identified using polyacrylamide gel electrophoresis. Whole-genome sequence analysis of those fifty-eight strains showed that the strains dominant during the first wave of prevalence (2014-17) carried animal RVA-derived VP1, NSP2, and NSP4 genes. However, the strains from the second wave of prevalence (2018-21) lost these genes, which were replaced with cognate human RVA-derived genes, thus creating strain with G8P[8] on a fully DS-1-like human RVA gene backbone. The G8 VP7 and P[8] VP4 genes underwent some point mutations but the phylogenetic lineages to which they belonged remained unchanged. We, therefore, propose a hypothesis regarding the tendency for the animal RVA-derived genes to be expelled from the backbone genes of the progeny strains after crossing the host species barrier. This study underlines the importance of long-term surveillance of circulating wild-type strains in order to better understand the adaptation process and the fate of newly emerging, animal-derived RVA among the human population. Further studies are warranted to disclose the molecular mechanisms by which spillover animal RVAs become readily transmissible among humans, and the roles played by the expulsion of animal-derived genes and herd immunity formed in the local population.