Strain-dependent norovirus bioaccumulation in oysters

Area of Science:

• Environmental microbiology
• Food safety
• Virology

Background:

• Noroviruses (NoVs) are a leading cause of human gastroenteritis and a significant cause of shellfish-related illness.
• NoV strains can bind to carbohydrate structures in shellfish, similar to human ligands, suggesting a role in bioaccumulation.
• Understanding NoV bioaccumulation in shellfish is crucial for public health and food safety.

Purpose of the Study:

• To compare the bioaccumulation efficiency and tissue distribution of different human norovirus strains in oysters (Crassostrea gigas).
• To investigate the influence of carbohydrate ligand specificity on norovirus bioaccumulation in oysters.
• To determine if seasonal variations affect norovirus bioaccumulation in oysters.

Main Methods:

• Oysters (Crassostrea gigas) were exposed to three distinct norovirus strains (GI.1, GII.3, GII.4).
• Bioaccumulation levels and tissue distribution (digestive tissues, gills, mantle) were quantified for each strain.
• Expression of specific carbohydrate ligands in oyster tissues was analyzed and correlated with viral load.
• Seasonal variations in bioaccumulation were assessed by conducting experiments during different months.

Main Results:

• Significant differences in bioaccumulation were observed among the tested norovirus strains.
• The GI.1 strain showed the highest bioaccumulation efficiency, primarily in digestive tissues, in a dose-dependent manner, with higher levels during colder months.
• The GII.4 strain exhibited very low bioaccumulation across all tissues, irrespective of season.
• The GII.3 strain demonstrated intermediate bioaccumulation, initially in gills and mantle, then concentrating in digestive tissues, without a clear seasonal effect.
• Strain-specific carbohydrate ligand binding correlated with observed bioaccumulation patterns.

Conclusions:

• Carbohydrate ligand specificity is a key factor determining norovirus bioaccumulation in oysters.
• Binding to digestive-tissue-specific ligands promotes efficient bioaccumulation of certain norovirus strains.
• Binding to sialic acid-containing ligands may lead to virus retention and clearance in non-digestive tissues like gills and mantle.