| Background and ObjectiveNorovirus is one of the major pathogens causing bacterial gastroenteritis in humans.There were 55%-85%reported outbreaks caused by G?.4 No ? worldwide.Bivalve shellfish are considered to be the food at high risk of being associated with foodborne outbreaks,and most reported outbreaks associated with oysters in Guangdong seafood industry development.Previous studies found that the NoVs contamination rate was higher in oysters from Changsha Bay oyster culture area of Shanwei City of Guangdong province.However,the incidence rate of acute gastroenteritis in population was 0.10 times per person in the breeding area,lower than the average rate of Guangdong province which is 0.25 times per person,also lower than the level of the whole country which is 0.56 times per person year.The positive rate of acute gastroenteritis cases caused by NoVs was 20%.In a survey of NoVs infection of population in Changsha bay,the overall latent infection rate of NoVs was 4.04%,and the latent infection rate of NoVs was 6.30%in oyster culture area.People living in the culture area have the habit of eating raw shellfish perennial,the chance of exposure to infection is relatively higher.However,there is little outbreak or epidemic of acute gastroenteritis caused by NoVs was reported.Despite the high exposure to NoVs pollution in aquaculture area environment,also have special high-risk diet,the incidence of acute gastroenteritis of the residents in oyster culture area is not higher than the general population.Whether there is some protection mechanism of the host is not easy to disease,that is worthy of studying and researching.Human infection with NoVs is mainly related to three factors:host heredity and immunity,environment and pathogen.A large number of studies have shown that NoVs infection is closely related to human histo-blood group antigen(HBGA)receptors.HBGA is a complex carbohydrate located on the surface of epithelial cells,red blood cell,respiratory tract,urogenital tract and digestive tract.It is therefore found in saliva,blood,breast milk and intestinal tract.Many studies have found that the presence of serum specific antibodies can block the combination of NoVs Virus like particle(VLP)and HBGA,protect the body from infection and reduce the risk of disease.What is the specific antibody level of the specific serum antibody by NoVs infection of the population in oyster culture area?The presence of serum antibodies has a higher capacity to block the combination of NoVs and HBGA receptors than in the general population?This study from the three aspects of population occupation and special diet,HBGA receptor distribution and serum antibody of the population exposed to any possible factors of NoVs infection for the population in high risk explore of oyster culture region that had fewer acute gastroenteritis outbreak caused by NoVs.MethodIn this study,two villages in A and B towns in oyster culture area were selected as survey site,and the residents aged 18 and over were investigated in the survey site.The questionnaire was designed according to their special occupation and dietary habits,blood and saliva samples were collected in the meantime.Serum samples from the general population of the inland region of Guangdong were also matched for age and sex as control group.The prokaryotic expression system of mature Escherichia coli BL21(DE3)was used to express NoV G?.4 VA387 P particles and NoV G?.17 P proteins as alternative antigens.The serum specific antibody levels of the GII.17 NoV epidemic strains were determined by indirect ELISA and the salivary HBGA receptor phenotype was determined by ELISA.In vitro neutralization assay was used as an in vitro neutralization model to determine the efficiency of serum antibodies blocking G?.4 No ? and HBGA receptors binding,and to analyze the relationship between NoVs infection and receptor blockade in the oyster culture area.Results1.A total of 195 people,70 males and 125 females with an average age of 50.7 years participated in the questionnaire and sampling(blood,saliva).,.The average age distribution of the population in A town was larger than that in B Town,and the difference was statistically significant(F=9.28,P=0.003).The number of women surveyed in B town was higher than that in A town,and the gender differences between A and B towns were statistically significant(?2=5.452,P=0.02).The crowd had a habit of eating pickled oyster special diet,and those who ate more than 1 times in the monthly frequency accounted for 24.6%(48/195)of people.Oyster farming or engagement in related work of oyster processing had 74 people,accounting for 37.9%(74/195),the difference between the two groups was statistically significant town occupation(?2?118.039,P<0.001).2.SDS-PAGE electrophoresis showed that the relative molecular weights were 36kDa NoV G?.4 VA387 P particle and 60kDa NoV G?.17 P protein,and was in accordance with the predicted size.3.The total positive rate of serum antibody against GIL 17 NoV protein in oyster culture area was 88.2%(172/195).The positive rate of serum antibody against G?.17 NoV P protein was 93.2%in breeding/processing occupations,the positive rate of serum antibody against G?.17 NoV P protein in non breeding/processing population was 81.8%,and the difference was statistically significant(?2=5.025,P=0.025).The special dietary habits of raw seafood were not found to affect the positive rate of serum antibodies against G?.17 NoV P protein.4.These 195 saliva HBGA receptor phenotypes showed that there were 168 secretor types,including 43 A type,41 B type,80 O type,4 AB type,27 non-secretor type.The 168 secretor types accounted for 86.2%(168/195),which was consistent with the proportion of salivary HBGA secretor receptors in Chinese general population.5.The serum antibody of population in oyster culture area blocking G?.4 NoV and HBGA receptor binding capacity reached 50%(BT50)accounting for 69.7%(136/195)and the average level of serum antibody titer in the general population was 1:212.30.The serum antibody of population in inland city blocking G?.4 NoV and HBGA receptor binding capacity reached 50%(BT50)with 106 people accounting for 62.7%(106/169).The average level of serum antibody titer was 1:99.09.The serum antibody in two areas of blocking capability reached 50%had no statistical significant difference(P>0.05);but there was a significant difference between the median total serum antibody titers of two areas(z=6.235,P<0.001).The blocking effect of serum antibody titer in the general population in oyster culture area is higher than the general population in inland region.Conclusion1.NoV G?.4 VA387 P particle and NoV G?.17 P protein were successfully expressed.2.High level of G?.17 NoV IgG antibodies have been detected in the serum of population in oyster culture areas,before the prevalence of the new G?.17 NoV variant,it is indicated that the population of the breeding area does have more chance of exposure and infection NoVs.3.The proportion of salivary HBGA secretory receptors in the oyster culture area is consistent with that of other populations in China,that excluding the congenital factors which are not susceptible to NoVs from the host genetic factors.4.The serum antibody titer of the blocking effect of populations in oyster culture areas was found to be higher than the general population in inland city,showed that the serum antibody of blocking ability in populations in oyster culture areas is better than the general population in inland city,suggesting that the population of oyster culture area is more immunity resistant infected G?.4 No ?. |
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