Metagenomic analysis and genomic characterization of enterovirus A76 and Norovirus GI.6[P11] co-infection in a patient with acute gastroenteritis in Thailand

Acute gastroenteritis (AGE) remains a significant global health concern, with noroviruses among the most prevalent viral pathogens. However, other enteric viruses also contribute substantially to the public health burden. This study provides the first molecular characterization of a co-infection involving a rarely reported enterovirus A76 (EV-A76) and a norovirus GI.6[P11] in a patient from Thailand. Metagenomic sequencing successfully identified complete viral genomes, revealing unique genetic variations. Phylogenetic analysis demonstrated that the EV-A76 strain shares high nucleotide similarity with a recently reported strain from Nepal, distinguishing it from previously identified recombinant strains. The amino acid sequence alignment of the complete EV-A76 genome revealed several distinctive amino acid substitutions compared to the most closely related strains. Notably, variations in the VP1 C-terminus and VP2 EF loop, known for high variability, were observed. These regions, crucial for epitope formation, are particularly susceptible to high-frequency mutations. This study reports the first documented co-infection of EV-A76 and norovirus GI.6[P11] in a single sample, identified through metagenomic sequencing in an AGE case in Thailand in 2023. The observed genetic variations highlight the necessity for ongoing monitoring of viral diversity to strengthen genomic surveillance and inform prevention strategies, especially for emerging pathogens with significant public health implications.