Depuration kinetics of murine norovirus in shellfish

This study evaluates and compares the uptake rates and depuration kinetics of murine norovirus (MNV-1), as a human norovirus surrogate, in Manila clams (Venerupis philippinarum) and Mediterranean mussels (Mytilus galloprovincialis). Ten trials of 70kg/trial (five with each mollusk) were performed. Mollusks were subjected to a controlled bioaccumulation step of 24h with 10²pfu MNV-1/mL seawater. Then, mollusks were relocated in an experimental depuration system for 7days. Viral contamination was quantified after bioaccumulation and then daily during depuration by reverse transcription-real time PCR (RT-qPCR) with TaqMan probes. Infectivity assays were conducted to test the presence of infectious viral particles at the end of the depuration period. Results showed significant differences in the uptake and removal viral rates between molluscan species. The average viral uptake for clams and mussels were 5.4×10⁶ and 4.0×10⁵RNA copies/g digestive tissue respectively, representing an uptake rate >90% higher in clams. The average reductions with regard to the initial levels were 60.5% for clams and 91.6% for mussels. On the other hand, a similar logarithmic trend line in MNV-1 depuration kinetics was observed in both bivalves, with two differentiated phases: an initial rapid reduction of viruses during the first 24-72h of depuration, and a subsequent stabilization with a slower depuration rate. All trials with clams and mussels showed significant viral reductions but remaining virus were still infectious at the end of the process.