Molecular epidemiology of DS-1-like G1P[8] rotavirus strains in Vietnam, 2012-2016: Evolutionary dynamics of an unusual rotavirus reassortant.

The segmented genome of Rotavirus alphagastroenteritidis facilitates the emergence of unusual reassortants, increasingly documented in the post-vaccine era. However, their long-term evolutionary dynamics and population-level persistence remain poorly understood. We investigated G1P[8] strains detected through hospital-based surveillance in northern and central Vietnam from 2012 to 2016. Electropherotyping, whole-genome sequencing, and phylogenetic analyses were performed to define genomic constellations and reconstruct evolutionary dynamics of DS-1-like reassortants. We documented four-year circulation patterns of DS-1-like G1P[8] strains, emerging in 2012/2013, peaking in mid-2014, and declining by 2016. Among 44 strains exhibiting short electropherotypes, at least three sequential genotype constellations (A-C) were identified: Constellation A likely arose in northern Vietnam through inter-genogroup reassortment between Wa-like G1P[8] (VP7/VP4) and DS-1-like G2P[4] strains; A related variant in central Vietnam suggested regional transmission from contemporaneous strains reported in Thailand and Japan; Constellation B involved acquisition of a Wa-like NSP2 gene; Constellation C included additional reassortment with bovine-like NSP2 and NSP4 genes from a co-circulating G8P[8] strain. No significant differences in clinical severity were observed between DS-1-like and Wa-like infections, and no cases of either genotype were detected among fully vaccinated children. Overall, this study describes a stepwise reassortment process involving intergenogroup, intragenogroup, and potential zoonotic events. Genomic diversification in this setting was not associated with increased virulence or evidence of immune escape. These findings highlight the need for continued genomic surveillance and broader sampling to better resolve the evolutionary dynamics of rotavirus reassortants.