Monitoring And Analysis Of Main Foodborne Viruses In Marine Shellfish In Zhoushan City

Food-borne viruses are major risk factors for food safety.Food-borne diseases and their viruses have considerable numbers and types,among which there are many diseases with wide epidemic scope,strong infectivity,easy to epidemic,easy to outbreak and may cause serious hazard.Therefore,this kind of virus is not only a harmful factor in the field of food safety,but also a major threat to improve people's public health and nutritional health levels.Some of these viruses are also the focus of WHO monitoring and funding research Food-borne viruses are usually parasitic in shellfish such as oysters and clams,so raw contaminated seafood products are most likely to cause infection.However,residents in our city have the habit of eating raw shellfish such as clams and oysters.Therefore,understanding the pollution status of various common food-borne viruses in raw seafood shellfish in Zhoushan city and analyzing the monitoring results will provide the basis for prevention and early warning of food-borne diseases,which is of great practical significance to public health,nutritional health and disease prevention in our city.From June 2015 to May 2016,monthly samples of cockles,mussels and wild oysters were collected from two aquaculture farms in Daidong and Dongsha,Daishan County,Zhoushan City,and from different stalls of Donghe Aquatic Products Market in Putuo District.Totaling 466 samples of shellfish were collected: 168 samples of cockles were collected from farms,94 samples of cockles,101 samples of oysters and 103 samples of mussels were collected from retail market,.Because of the low concentration of virus in marine shellfish,the successful detection of food-borne virus depends on whether the virus can be effectively activated and whether high-purity and complete nucleic acid can be obtained after the sample is processed.So we optimized the detection method.Firstly concentrated and enriched the virus before detection,then extracted the nucleic acid of food-borne virus,and use fluorescence quantitative RT-PCR method to detected Norovirus type I/II Norovirus(NV),Rotavirus(RV),Sapovirus(SPV),Astrovirus(As V),Hepatitis A virus(HAV),Hepatitis E virus(HEV),intestinal Adenovirus(Ad V)and other major food-borne viruses.A total of 89 virus-positive samples were detected in 466 shellfish samples,with a total positive rate of 19.10%.The total positive rates of clam samples collected from farms and retail markets were10.71% and 21.28%,respectively,with statistical differences(X2= 5.432,P<0.05),while the totalpositive rates of three different shellfish(cockles,oysters and mussels)collected from farmers markets were 21.28%,26.73% and 19.10%,respectively,with no statistical differences among different shellfish types(X2= 0.822,P>0.1).Except norovirus type I,hepatitis A virus and rotavirus were not detected,the positive rate of norovirus type II was 4.08%(19/466),9.66%(45/466)of cerulovirus,2.79%(13/466)of astrovirus,1.07%(5/466)of hepatitis E virus,1.50%(7/466)of intestinal adenovirus.The positive rates of different viruses were statistically different(X2=61.028,P<0.001).The results of contamination status of various food-borne viruses in three kinds of local marine shellfish in Zhoushan city showed that among 466 marine shellfish(cockles,oysters and mussels)samples collected from cockle farms and retail markets from 2015 to 2016,norovirus type II,cerulovirus,astrovirus,hepatitis E virus and intestinal adenovirus were detected,with cerulovirus having the highest detection rate,followed by norovirus type II.Norovirus type I,hepatitis A virus and rotavirus were not detected in all shellfish.According to the sampling time,food-borne viruses were detected all year round.The positive rate of foodborne viruses in marine shellfish in spring and winter was significantly higher than that in summer and autumn.Norovirus type II and Zaru virus had obvious seasonality.The positive samples were mainly in spring and winter,and the detection of other food-borne viruses had no obvious seasonal difference.The positive rate of different types of sample viruses from retail market had obvious seasonality.The positive rate in spring and winter was significantly higher than that in summer,while the positive rate of positive viruses in farm cockles had no seasonal difference.This monitoring found that the positive rate of food-borne virus in cockles collected from retail markets was significantly higher than that of cockles collected from cockles farms,especially the norovirus type II.The two cockles farms investigated in this survey are open-farms,which are enclosed in the sea and have no residential living area around them.Flowing seawater makes the breeding environment of farms changing all the time,and the sampling randomness of farms is low,thus reducing the pollution situation.The sampling randomness of retail markets is high,and the probability of contamination was relatively high.In addition,the poor environment of retail farmers' markets was easy to cause cross-contamination,which leads to serious virus pollution.Mussels were one of Zhoushan's local cultured shellfish.It was mainly cultured in Shengsi County,Zhoushan City.Due to the remoteness of the cultured base,only mussels sold in farmers' markets were collected in this monitoring.The monitoring results showed that the contamination of food-borne viruses was notoptimistic,the positive rate of Zaru virus and Norovirus were relatively high.However,different from cockles and wild oysters,mussels were not only the local people's favorite food,but also sold to all parts of the country and even were made into dry goods for export abroad.Therefore,it was suggested to further develop the food-borne nature of mussels cultured in Zhoushan's farms.The contamination status of food-borne viruses in marine shellfish in Zhoushan city was not optimistic.The positive detection rates of various food-borne viruses were distributed seasonally,mainly in winter and spring.However,as Zhoushan city was a tourist city with a large number of tourists,the risk of food-borne diseases may increase in summer and autumn.Therefore,while strengthening the prevention and control in winter and spring,the monitoring work in summer and autumn should be strengthened at the same time.