Study Of Norovirus Contamination On Strawberry And Irrigation Water

Norovirus(No V)is a major pathogen of non-bacterial gastroenteritis worldwide,which seriously threatens human health.In China,the common genotypes of No V disease outbreaks in the population are GI and GⅡ.At present,there are no preventive vaccines and therapeutic drugs for the diseases caused by No V,the detection of No V is the key to prevent disease outbreaks.In recent years,the number of outbreaks associated with fresh produce has increased significantly worldwide.Fresh produce such as strawberries and lettuce have been confirmed to be the main food vector of No V.A number of foreign studies have shown that contaminated irrigation water can transfer pathogens to fresh produce and cause contamination.The researches of the No V contamination on fresh produce started late in China.The contamination and potential sources of No V on strawberries in Jiangsu province and its surrounding areas remain unclear.In this study,the strawberries and irrigation water collected in Jiangsu and its surrounding areas were taken as the research objects.The RT-q PCR molecular detection and genotyping was used to investigate the No V contamination on strawberries and irrigation water,and its correlation was analyzed.The main findings are shown as below:(1)The No V contamination of strawberries in Jiangsu and surrounding areas was investigated.The No V GI and GⅡ molecular detections of 130 strawberry samples,collected from strawberry production bases in Yancheng,Nanjing,Zhenjiang,Shanghai were completed.The No V contaiminaton on strawberries were found in this study.The detection rate of No V GI(34.62%)was higher than that of No V GⅡ(12.31%).There were obvious differences for No V detection rates in different regions.The No V detection rates of strawberries in Yancheng,Zhenjiang,Nanjing,and Shanghai were 50%,43.18%,38.89%,and 16.67%,respectively.There were also great differences between No V detection rates in different months.The months with the highest detection rate of No V in strawberry samples are January(76.67%),March(50%),and April(40%).(2)A enrichment method of No V in irrigation water samples combined with suction filtration and tangential flow technology was established.After the irrigation water sample is filtered through two pore sizes filter membrane,then filtrate is circulated and eluted in the tangential flow system and the virus is continuously concentrated.The recovery experiment and molecular detection was perfermed after adding No V in irrigation water samples.The results showed that the total recovery of No V GI was 43.91%-60.08%,and the limit of detection was 4.48 GC/m L;the total recovery rate of No V GⅡ was 22.29%-53.57%,and the limit of detection was 11 GC/m L.This method can be used for the enrichment of viruses from agricultural irrigation water.(3)No V contamination of strawberry irrigation water samples in Jiangsu and surrounding areas was investigated.The No V detections for 60 irrigation water samples were completed.The No V contaminations were found and the detection rate of irrigation water samples was 65%,which was higher than that of strawberry samples.The detection rate of No V GⅡ was 53.33%,which was higher than that of No V GI(28.33%).The detection rates of strawberry irrigation water in Shanghai,Nanjing,Zhenjiang,and Yancheng were 75%,66.67%,63.64%,and 58.33%,respectively,with higher detection rate of No V GⅡ.The months with higher detection rates of No V were March(100%),April(100%),and January(90%)in 2021.(4)The analysis of No V contamination and correlation on strawberry and irrigation water samples: The same No V GI or GⅡ type was found in strawberries and its corresponding irrigation water samples.The No V detection rates of irrigation water samples between No V GI positive and negative strawberry samples were significantly different,the detection rate of GI No V in strawberries was 41.18% in irrigation water contaminated with GI No V,and 26.13%in strawberries with no GI No V contamination.While that of No V GⅡ were not significant.The No V contaminated irrigation water may be a potential No V contamination source for strawberry preharvest.In conclusion,No V contamination were found on strawberries and corresponding irrigation water in Jiangsu and surrounding areas,with the similar.No V GI or GⅡ type found on strawberries and its irrigation water in same production sites.The No V contaminated irrigation water may be one of the potential sources for No V contamination on strawberries during harvest seasons.This study provides scientific support for controlling the contamination of strawberries by strengthening the prevention and control of No V in irrigation water source.