Evaluation of methods measuring the capsid integrity and/or functions of noroviruses by heat inactivation

Attempts were made to evaluate methods measuring the capsid integrity and/or functions of noroviruses (NoVs) following heat treatment. Intact viruses (Murine Norovirus-1 [MNV-1] and human NoV GII.4), virus like particles (VLPs) and P particles (expressed in vitro from the protruding domain of the viral capsid) of NoVs were used in this study. Following heat treatment, no significant difference of viral titer of MNV-1 versus NoV GII.4 was observed by RNase One RT-PCR or cell-binding RT-PCR, although cell-binding RT-PCR (to measure the capsid functions) revealed higher reductions than RNase One RT-PCR (to measure the capsid integrity). These results indicate that the function assay for receptor binding is more sensitive than the capsid integrity assay to measure the protected viral RNA. MNV-1 could be used as a surrogate for human NoVs by heat inactivation from the perspective of capsid integrity and/or functions. The heat resistance varied among different GI and GII NoV strains when their P particles were studied.