The oral in fecal-oral: Exploring the overlooked relationship between saliva and enteric viruses

The oral cavity serves as a critical but often underexplored interface in the ecology and transmission of enteric viruses. A growing body of research has shown that various human enteric viruses, including norovirus and hepatitis A virus, can be detected in oral fluids and saliva, although typically at lower concentrations compared to those found in feces. Beyond detection, experimental studies in animal models and limited human tissue data suggest that some enteric viruses, notably norovirus, can actively replicate within the cells of salivary glands and oral mucosa, rather than merely passing through the oral cavity through ingestion or vomit from the gastrointestinal tract. This replication can lead to local viral shedding into saliva, adding complexity to the traditional understanding of enteric virus transmission as purely fecal-oral. Despite this growing research, significant gaps remain, particularly regarding the kinetics of enteric viral decay in saliva, strain-specific replication dynamics, and the role of salivary antiviral components in modulating viral infectivity. Addressing these questions could improve microbial risk assessment modeling, refine disease outbreak modeling, and open new avenues for diagnostics and prevention. Collectively, understanding how enteric viruses replicate, survive, and interact with the unique immune environment of the oral cavity is essential to fully characterizing their transmission potential and public health significance. This review summarizes the current literature on enteric viruses and saliva, discussing some of the challenges and opportunities for future development in this new field.