Inactivation of murine norovirus, feline calicivirus and echovirus 12 as surrogates for human norovirus (NoV) and coliphage (F+) MS2 by ultraviolet light (254 nm) and the effect of cell association on UV inactivation

Aims: To determine inactivation profiles of three human norovirus (NoV) surrogate viruses and coliphage MS2 by ultraviolet (UV) irradiation and the protective effect of cell association on UV inactivation. Methods and Results: The inactivation rate for cell‐free virus or intracellular echovirus 12 was determined by exposure to 254‐nm UV light at fluence up to 100 mJ cm^?2. The infectivity of murine norovirus (MNV), feline calicivirus (FCV) and echovirus 12 was determined by cell culture infectivity in susceptible host cell lines, and MS2 infectivity was plaque assayed on Escherichia coli host cells. The UV fluencies to achieve 4‐log₁₀ inactivation were 25, 29, 30 and 70 (mJ cm^?2) for cell‐free FCV, MNV, echovirus 12 and MS2, respectively. However, a UV fluence of 85 mJ cm^?2 was needed to inactivate intracellular echovirus 12 by 4 log₁₀. Conclusions: Murine norovirus and echoviruses 12 are more conservative surrogates than FCV to predict the UV inactivation response of human NoV. Intracellular echovirus 12 was 2·8‐fold more resistant to UV irradiation than cell‐free one. Significance and Impact of the Study: Variation in UV susceptibilities among NoV surrogate viruses and a likely protective effect of cell association on virus susceptibility to UV irradiation should be considered for effective control of human NoV in water.     

Efficacy of alcohol-based hand sanitizers against human norovirus using RNase-RT-qPCR with validation by human intestinal enteroid replication

Successful human norovirus (HuNoV) cultivation in stem cell-derived human intestinal enteroids (HIE) was recently reported. The purpose of this study was to evaluate the anti-HuNoV efficacy of two alcohol-based commercial hand sanitizers and 60% ethanol by suspension assay using RNase-RT-qPCR, with subsequent validation of efficacy by HuNoV cultivation using the HIE model. In suspension, when evaluated by RNase-RT-qPCR, 60% ethanol resulted in less than one log₁₀ reduction in HuNoV genome equivalent copies (GEC) regardless of contact time (30 or 60s) or soil load. The two commercial products outperformed 60% ethanol regardless of contact time or soil load, providing 2·2–3·2 log₁₀ HuNoV GEC reductions by suspension assay. Product B could not be validated in the HIE model due to cytotoxicity. Following a 60s exposure, viral replication in the HIE model increased 1·9 ± 0·2 log₁₀ HuNoV GEC for the neutralization (positive) control and increased 0·9 ± 0·2 log₁₀ HuNoV GEC in challenged HIE after treatment with 60% ethanol. No HuNoV replication in HIE was observed after a 60 s exposure to Product A.     

Antiviral effects of black raspberry (Rubus coreanus) seed extract and its polyphenolic compounds on norovirus surrogates

Black raspberry seeds, a byproduct of wine and juice production, contain large quantities of polyphenolic compounds. The antiviral effects of black raspberry seed extract (RCS) and its fraction with molecular weight less than 1 kDa (RCS-F1) were examined against food-borne viral surrogates, murine norovirus-1 (MNV-1) and feline calicivirus-F9 (FCV-F9). The maximal antiviral effect was achieved when RCS or RCS-F1 was added simultaneously to cells with MNV-1 or FCV-F9, reaching complete inhibition at 0.1–1 mg/mL. Transmission electron microscopy (TEM) images showed enlarged viral capsids or disruption (from 35 nm to up to 100 nm) by RCS-F1. Our results thus suggest that RCS-F1 can interfere with the attachment of viral surface protein to host cells. Further, two polyphenolic compounds derived from RCS-F1, cyanidin-3-glucoside (C3G) and gallic acid, identified by liquid chromatography-tandem mass spectrometry, showed inhibitory effects against the viruses. C3G was suggested to bind to MNV-1 RNA polymerase and to enlarge viral capsids using differential scanning fluorimetry and TEM, respectively.