Modeling the kinetics of norovirus GII bioaccumulation in mussels

Shellfish, whose feeding relies on filtering large volumes of water to obtain nutrients, are among the main sources of viral gastroenteritis. Beyond their role as a food safety risk requiring assessment, shellfish are also valuable for marine water bodies quality biomonitoring, as they can provide epidemiological insights into pathogen and chemical contaminants circulation in the population. Noroviruses are major agents responsible for foodborne illnesses, leading to a substantial economic burden worldwide. In this study, we have investigated the bioaccumulation kinetics of norovirus genogroup II in mussels by testing a mathematical model with frequentist and Bayesian approaches. Four experiments were conducted where 10 L of sea water were spiked with 300 μl of stool suspension with different viral concentration. Mussels' samples were collected at different time points from 0 h to 48 h. Viruses were extracted from the digestive gland following the ISO 15216 protocol, including a PEG concentration step. RNA was extracted, and amplification of DNA was performed using a commercial RT-qPCR kit. Results showed that, regardless of the initial water concentration, equilibrium was reached within 24 h. The time of first detection depended on the inoculum concentration (30 min, 4 h, and 24 h for the highest to lower concentrations), while no detection occurred at the lowest concentration. The Bayesian model predicted viral concentrations in mussel digestive tissues relative to seawater viral load. Noroviruses were bioaccumulated up to 1000-fold, highlighting mussels as sensitive biosensors. The model also provided insight into bioaccumulation mechanisms through hypothesis testing. This study focuses on bioaccumulation, whereas most previous works emphasized depuration. It provides new insights into the mechanisms of viral uptake in shellfish, underlining both the risk of contamination for consumers and the relevance of using Mytilus spp. as sentinels for marine biomonitoring.