Detection of Infectious Murine Norovirus on Fresh Produce through a Novel CRISPR/Cas13-based Sensitive Assay

Current standard food detection methods do not distinguish between infectious and non-infectious norovirus leading to uncertainty in the interpretation and management of a norovirus positive food sample. These methods also require expensive RT-qPCR based equipment. In contrast, CRISPR-based, compared to RT-qPCR based, detection methods yield similar sensitivity and specificity and are generally less expensive. The aim of this study was to detect norovirus with an intact capsid, a proxy for infectivity, through a CRISPR-Cas13a based detection method in conjunction with acapsid integrity assay. Our CRISPR method detected murine norovirus (MNV-1), with an intact capsid, at a limit of detection of 2.59 log10 gc/ 25 g (5 gc/ rx). This method did not cross-react with other targets (synthetic hepatitis A virus; human norovirus GI, GII; rotavirus). Compared with RT-qPCR, this CRISPR based method showed an increased sensitivity when detecting low copy numbers of RNase-pretreated MNV-1 in lettuce and blueberries samples. This is the first report describing a CRISPR-based detection of potentially infectious viruses in food samples.