Sphingobacterium-mediated EPS shielding exacerbates norovirus environmental persistence and risk in swine farms

Norovirus (NoV) is a major cause of epidemic acute gastroenteritis worldwide, and contaminated food and water are important routes of NoV transmission. However, the environmental fate of NoV and the factors contributing to its persistence remain poorly understood. This study investigated NoV occurrence in small-scale swine farm compost and intensive swine wastewater treatment systems (WWTSs), and explored the potential bacterial factors associated with viral persistence. NoV was detected in swine compost, with Sphingobacterium co-occurring in NoV-positive samples but not in NoV-negative samples. In an intensive swine WWTS, NoV remained detectable throughout all treatment units, with 10^7.3 copies L^-1 in the influent and 10^2.4 copies L^-1 still present in the final effluent. Scenario-based QMRA indicated that splash ingestion represented the dominant exposure pathway, with an estimated annual potential infection risk of 2.5%. Sphingobacterium abundance was positively associated with NoV loads across treatment units. Under heat, ultraviolet, and chlorine stress, Sphingobacterium-associated NoV showed up to 6.6-, 5.6-, and 2.5-fold higher RNA retention, respectively, and stronger infectivity than bacteria-free controls. Adhesion assays, transmission electron microscopy observation, and molecular docking suggested that Sphingobacterium extracellular polysaccharides (EPS) may interact with the NoV capsid P domain via hydrogen bonding, supporting a putative EPS-associated protective pathway. These findings suggest that Sphingobacterium-mediated EPS shielding may contribute to NoV persistence and disinfection tolerance in swine-farm waste systems, highlighting the need to integrate microbial control and routine NoV monitoring into viral-risk management strategies.