Evaluation Of Efficacy Of Duck Tembusu Virus Disease Inactivated Vaccine In Chickens And A Preliminary Study On Its Mechanism

Duck tembusu virus disease is an acute high contact infectious and all ages and varieties of duck susceptible disease caused by duck tembusu virus.With the degree of secondary infection,the morbidity of the disease can reach 100%,and the mortality rate varies from 5% to 30%.In recent years,the duck tembusu virus infection host increasing,including meat layers,laying hens,etc.No systemic research report on the pathogenicity of duck tembusu virus in chickens,this research using different duck tembusu virus strains isolated from different time for SPF(Specific pathogen Free,SPF)chicken artificial infection test and using the duck tambusu virus inactivated vaccine by different immune program for immune challenge test,immune efficacy evaluation of duck tembusu virus disease inactivated vaccine immune chicken and pathogenicity evaluation of chickens challenge with duck tembusu virus.The SPF chicken artificial infection model was conducted using duck tembusu virus(HB)strain,based on serological detection,virus isolation,pathological histological changes,and detection of cytokine m RNA expression levels in tissue and PBMC post challenged with virus.The results showed that the serum viremia was maintained for 2days after infection,the serum specific antibodies could be detected at 5 days after infection,the pathological histological damage of the brain,spleen,and reproductive system was not obvious in the early stage of infection,and the thymus and bursa of Fabricius damage started from the 5th days after infection and continued until the 7th days.The results of the cytokine detection showed that,Splenic IL-6 expression was significantly increased at the 5th days after challenge,IL-6 and IL-4 expression of the reproductive system also increased at 5d after infection,Both GZMA and IL-6 were significantly up-regulated in the brain from 1 to 7 days after challenge,Brain cytokine expression levels were all higher than those in the spleen and reproductive system,The brain is the main target organ of virus-infected chickens.For 21-day-old SPF chicken primary and secondary immunization two immunization program,respectively in 21 days after immunization challenge test,through the infection and blank control chicken serology,virus isolation,pathological histology observation,organs and PBMC cytokine m RNA expression levels detection,to evaluate the effectiveness of duck tembusu virus inactivated vaccine immune chicken.The results showed that 2 to 3 days after challenge,serum virus isolation was negative,indicating that vaccine immunization has good immune protection effect;histological changes were not obvious;cytokine test results showed that secondary immunization could reduce the expression of GZMA in the brain and spleen,reduce the damage of virus infection;vaccine immunization faster activate B cells in the spleen;vaccine immunization could increase the expression of IL-4 and IL-6 in PBMC,and reduce virus infection against IL-6,IL-4 and GZMA genes in PBMC,exert an immunoprotective function.56-day-old SPF chickens artificial infection test using two strains.Through the genetic evolution analysis of strain E gene,the antibody titer detection after challenge,serum virus isolation,the histological observation and the cytokine expression levels change in PBMC to analyze and compare the pathogenicity of 2 strains against chickens.The results showed that two strains belonged to the same branch,and the body response of two strains artificial infection was similar with HB strain.Serum specific antibodies appeared first in NC strain 5 days post infection,and viremia in NC strain was more severe than JA strain 1 days post infection,and there was no significant difference in cytokine expression in chicken PBMC of the two strains.Conclusion: Duck tembusu virus is less pathogenic in 56 days old SPF chickens and between different strains;there is no obvious pathological histological damage to spleen,reproductive system and brain,bursa and thymus has different degrees of pathological histological damage.Vaccine immunity can produce good immune protection effect,and its protective mechanism is related to increasing the expression of cytokines in PBMC,reducing the inhibition of PBMC cytokine expression by virus infection,and the early activation of B cells in the spleen.