Category Archives: Virus

Science Direct

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Norovirus in oysters is a significant food safety risk. A recent ISO detection method allows for reliable and repeatable estimates of norovirus concentrations in pooled samples, but there is insufficient data to estimate a distribution of copies per animal from this. The spread of norovirus accumulated across individual oysters is useful for risk assessment models. Six sets of thirty individual Crassostrea gigas oysters were tested for norovirus concentration levels by reverse-transcription quantitative PCR (RT-qPCR): three from a commercial harvest site, and three post-depuration. Five sets had norovirus GII means above the limit of quantification (LOQ), and one below the LOQ, but above the limit of detection. No norovirus GI was detected in pooled tests, and individual oysters were not tested for norovirus GI. Depuration was shown to reduce the mean concentration of GII copies, but not to affect the shape of the distribution around the mean. Deconvoluting the uncertainty of the method, the coefficient of variation was stationary (0.45 ± 0.2). The best fit distribution was either a lognormal distribution or a gamma. Multiplying these distributions by the weight of oyster digestive tissues gave an estimate for the count mean. This was used as the parameter λ in three compound Poisson distributions: Poisson-lognormal, Poisson-gamma, and Poisson-K. No model was found to fit better than the others, with advantages for each. All three could be used in future risk assessments. Preliminary validation of sampling uncertainty using repeated testing data from a previous study suggests that these results have predictive power.

Science Direct

Human noroviruses (HuNoVs) are the primary non-bacterial pathogens causing acute gastroenteritis worldwide. Here we reported a co-infection of HuNoVs with different genotypes during an outbreak of gastroenteritis in travelers. The aim was to trace the source and transmission patterns of the infections using next-generation sequencing (NGS). An investigation was conducted on a cross-border travel group who came back to China from Thailand for symptoms of gastroenteritis. Anal swabs were collected from 23 people and samples were analyzed using RT-qPCR. A total of 11 samples tested positive for HuNoVs. All samples tested negative for bacterial pathogens in the surveillance list. Positive samples for HuNoVs were further analyzed using NGS. Seven out of 11 positive samples were sequenced and 16 viral genome sequences for 10 different strains of HuNoVs were obtained. We demonstrated that the outbreak was associated with co-infection of multiple genotypes of HuNoVs and the source of infections was probably contaminated water or food. Besides, four different HuNoVs genotypes (GI.5[P12], GIX.1[GII·P15], GI.7[P7] and GII.8[P8]) were identified in one patient. Co-infection with both genogroup GI and GII, and co-infection with two different P types ([P10] and [P13]) of genotype GI.3 were identified in different patients. Findings from this study show that individuals can be simultaneously infected with multiple strains of HuNoVs and NGS can help investigating these issues. Further, this study shows that food and water are potential vehicles for transmission of multiple foodborne viruses.