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This study investigates the evolutionary dynamics of norovirus GII.4 lineages circulating in the Amazon region of Brazil, with a particular focus on the recently emerged GII.4 San Francisco variant. A molecular descriptive design was employed, analyzing 615 stool samples from gastroenteritis patients collected between November 2023 and December 2024. Norovirus prevalence was 14.5%, with genotype characterization revealing a diverse array of circulating genotypes: GII·P31/GII.4, GII·P17/GII.17, GII·P16/GII.4, GII·P8/GII.8, GII·P7/GII.6, GII·P16/GII.10, and GII·P7/GII.7. Phylogenetic reconstruction and molecular clock analyses, performed using Bayesian inference in BEAST, demonstrated that Brazilian GII.4 strains are closely related to global lineages and highlighted rapid viral evolution, with a substitution rate of 2.28 × 10 −4 substitutions/site/year. The GII.4 San Francisco variant, likely derived from the GII·P16/GII.4- Sydney_2012, was detected for the first time in Brazil, and a key recombination event was identified between the GII·P16 type and the GII.10 genotype. The research underscores substantial genetic diversity and ongoing evolution of norovirus in this region, emphasizing the necessity for continuous genomic surveillance to detect emerging variants and guide public health initiatives. • First detection of the GII.4 San Francisco norovirus variant in the Amazon region of Brazil. • High genetic diversity of norovirus, including multiple circulating recombinant strains. • Bayesian phylogenetic and molecular clock analyses reveal Brazilian GII.4 strains are closely related to global lineages. • Identification of rapid viral evolution (2.28 × 10 −4 substitutions/site/year) and a major recombination event involving GII.P16/GII.10. • Findings underscore the necessity of continuous genomic surveillance to detect emerging norovirus variants and guide public health responses.
TL;DRPhylogenetic reconstruction and molecular clock analyses demonstrated that Brazilian GII.4 strains are closely related to global lineages and highlighted rapid viral evolution, with a substitution rate of 2.28 × 10-4 substitutions/site/year. (Semantic Scholar)