Norovirus GI.5 [P4]: first report of the rare norovirus recombinant variant in Northeastern Mexico and its global epidemiological context.

Norovirus is the primary cause of acute gastroenteritis outbreaks, considerably impacting children under 5 years, followed by older adults and immunocompromised individuals. As an RNA virus, norovirus exhibits high genetic variability, driven by recombination events at the ORF1-ORF2 junction. This study reports the first detection of the rare norovirus GI.5 [P4] variant in Northeastern Mexico, identified in a single positive isolate (MTY0115; GenBank: PQ369661) from a sample group of 386 individuals, with a prevalence of 0.25%. Notably, norovirus GII was not detected. Phylogenetic analysis of the partial RdRp/VP1 region revealed clustering with global GI.5 [P4] sequences, revealing evolutionary relationships with isolates from Asia, Europe, and America. A recombination event was identified at position 5307 (breakpoint based on reference sequences of GI.5 [P5] and GI.4 [P4]) within ORF1, with genetic inheritance from a GI.5 [P5] isolate from Moscow, Russia, and a GI.4 [P4] isolate from France. Typing classification through sequencing of overlapping ORF1 and ORF2 regions is valuable for understanding genomic variations and their epidemiological impact on at-risk and non-risk populations.