Temperature-Dependent Persistence of Human Norovirus Within Oysters (Crassostrea virginica)

This study characterizes the persistence of human norovirus in Eastern oysters (Crassostrea virginica) held at different seawater temperatures. Oysters were contaminated with human norovirus GI.1 (Norwalk strain 8FIIa) by exposing them to virus-contaminated water at 15 °C, and subsequently holding them at 7, 15, and 25 °C for up to 6 weeks. Viral RNA was extracted from oyster tissue and hemocytes and quantitated by RT-qPCR. Norovirus was detected in hemocytes and oysters held at 7 and 15 °C for 6 weeks and in hemocytes and oysters held at 25 °C for up to 2 and 4 weeks, respectively. Results confirm that NoV is quite persistent within oysters and demonstrate that cooler water temperatures extend norovirus clearance times. This study suggests a need for substantial relay times to remove norovirus from contaminated shellfish and suggests that regulatory authorities should consider the effects of water temperature after a suspected episodic norovirus-contamination event.