Sensitivity of Murine Norovirus and Hepatitis A Virus to E-beam Irradiation in Whole Oyster and Oyster Homogenate

Introduction: Shellfish are known to concentrate enteric viral and bacterial pathogens. Consumption of raw and uncooked oysters increases the risk of foodborne infections. Among the enteric viruses, noroviruses and hepatitis A virus (HAV) are of significance to the shellfish industry and to public health.

Purpose: To demonstrate the potential of E-beam irradiation processing as a pathogen kill-step to reduce or eliminate HAV and norovirus in shellfish.

Methods: Live oysters (Crassostrea virginica) were contaminated under simulated natural conditions with HAV and murine norovirus (MNV-1) in accumulation tanks. These whole oysters as well as oyster homogenates were subjected to E-beam irradiation at different doses ranging from 0.5 kGy to 5.5 kGy. The samples were processed to extract the viruses and plaque assays were performed for viral quantification using specific cell lines for MNV-1 (RAW 264.7) and HAV (FRhK-4), respectively. E-beam dose required to bring about 1-log reduction in the viral titer (D₁₀value) and percentage reduction in viral titer at different E-beam doses was determined for MNV-1 and HAV in both whole oyster samples and oyster homogenate.

Results: D₁₀ values of MNV and HAV in oyster homogenate were 4.96 ± 0.6 kGy and 5.74 ± 0.8 kGy, which were not significantly different from that of the whole oysters (4.56 ± 1.8 and 5.6 ± 2.3 kGy, respectively). The D₁₀values of MNV-1 and HAV were high in both whole oyster and oyster homogenate indicating that oyster meat protects enteric viruses from ionizing radiation. However, at the current FDA approved maximum dose of 5.5 kGy, the use of E-beam irradiation of oyster homogenate will achieve a 91.2% and 92.5% reduction in MNV and HAV, respectively. In whole oysters, the reduction will be 90.3% and 86.7% for MNV and HAV, respectively.

Significance: The results suggest that E-beam inactivation at current FDA approved dose will result in a defined reduction of enteric viruses in oysters, which in turn can translate into reduction in shellfish-associated human illnesses.