Thermal inactivation of enteric viruses and bioaccumulation of enteric foodborne viruses in live oysters (Crassostrea virginica)

Authors: ARAUD, ELBASHIR - The Ohio State University; DICAPRIO, ERIN - The Ohio State University; MA, YUANMEI - The Ohio State University; LOU, FANGFEI - The Ohio State University; Kingsley, David; HUGHES, JOHN - The Ohio State University; LI, JIANRONG - The Ohio State University

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2016
Publication Date: 6/15/2016
Citation: Araud, E., Dicaprio, E., Ma, Y., Lou, F., Kingsley, D.H., Hughes, J.H., Li, J. 2016. Thermal inactivation of enteric viruses and bioaccumulation of enteric foodborne viruses in live oysters (Crassostrea virginica). Applied and Environmental Microbiology. 82:2086-2099.

Interpretive Summary: Cooking temperatures are a critical issue for seafood safety. In this manuscript, the thermal sensitivity of the foodborne viruses hepatitis A virus, rotavirus, norovirus surrogates, murine norovirus and Tulane Virus, as well as human norovirus GII.4 was assessed. This was performed both on relatively pure virus stocks, as well as live oysters contaminated with these viruses. Results indicate that cooking oysters to 80 degrees C for 6 minutes was sufficient to inactivate rotavirus, murine norovirus, and Tulane virus. Also results indicate that viruses sequestered within oysters are more thermally resistant than pure virus stocks. However at 80 degrees C, HAV was not inactivated and human norovirus GII.4 apparently was also not inactivated, as judged by were the PGM-MB virus receptor binding assay. Experiments with Tulane virus which binds to the PGMs in a manner similar to human norovirus indicates that thermal inactivation of this virus occurs well before the loss on PGM-binding, inferring that loss of receptor binding ability may not be the primary mechanism that results in thermal inactivation. Bioaccumulation experiments indicate that all viruses are efficiently bioaccumulated within oyster tissues when in growing waters and some minor differences in the tissue distribution pattern of these within different oyster tissues was noted. In total, these experiments provide guidance as to appropriate cooking temperatures for oysters.

Technical Abstract: Human enteric viruses are one of the main causative agents of shellfish associated outbreaks. In this study, the kinetics of viral bioaccumulation in live oysters and the heat stability of the most predominant enteric viruses were determined in both tissue culture and in oyster tissues. A human norovirus (HuNoV) GII.4 strain, HuNoV surrogates [murine norovirus (MNV-1); Tulane virus (TV)], hepatitis A virus (HAV), and human rotavirus (RV) were bioaccumulated to a high titer within the oyster tissues with different patterns of bioaccumulation for each virus. We tested the thermal stability of each virus at 62, 72, and 80 degrees C in culture medium. The viruses can be ranked from the most heat resistant to the least stable as: HAV, RV, TV, then MNV-1. In addition we found that oyster tissues provided a protective effect to the virus during heat treatment. To decipher the mechanism underlying viral inactivation by heat, purified TV was treated at 80 degrees C for increasing time intervals. It was found that the integrity of viral capsid was disrupted whereas viral genomic RNA remained intact. Interestingly, heat treatment leading to complete loss of TV infectivity was not sufficient to completely disrupt the receptor binding activity of TV as determined by the porcine gastric mucin magnetic bead binding assay. Similarly, HuNoV VLPs and a HuNoV GII.4 strain retained some receptor binding ability following heat treatment. Although foodborne viruses have variable heat stability, 80 degrees C for greater than 6 min was sufficient to completely inactivate most enteric viruses in oysters, with the exception of HAV.