Analysis On The Immune Effect Of Avian Influenza Vaccine In Linzi

Avian influenza is one of the major infectious diseases affecting poultry breeding industry,which seriously affects the development of stockbreeding.The highly pathogenic avian influenza viruses represented by H5N1,H5N6,H5N8 and H7N9,and low pathogenic avian influenza viruses represented by H9N2 have been successfully transmitted to poultry and circulating in poultry chronically.Immunization is the most effective measure to control avian influenza,and often caused immune failure due to mutation of avian influenza virus.Accordingly,need to monitor the information in poultry and immunity of poultry avian influenza vaccine,make relevant measures to outbreak in timely.Linzi District was as the center in this study,and evaluated the effectiveness of avian influenza vaccine in the farms through regular and sampling inspection,so as to further understand the shortcomings in the prevention and control,and provide suggestions in production.Secondly,an H9N2 avian influenza virus was isolated from a commercial chicken farm,and the evolutionary relationship and pathogenicity were analyzed,to further understand the epidemic trend in Linzi and provide some suggestions for the prevention and control of the disease.The research results are as follows:1.Immunization effect evaluation of avian influenza vaccine in poultry in LinziAll broilers,laying hens and meat ducks in Linzi were immune with “H5N1 Re-11 + Re-12,H7N9 H7 Re-2 strains” inactivated vaccine.A total of 1682 samples were collected from September 2019 to June 2021（241 samples were spot check）,including 1016 layers,391 broilers and 275 ducks.First,serum samples were evaluated using different H5 subtype standard antigens.The qualification rate was more than 82.94% using Re-11 and Re-12,while the qualification rate was only 50.54% using Re-8,indicating that the corresponding standard antigen should be used for avian influenza antibody detection.The qualification rate of H7 antibody was 83.17%.Subsequently,we analyzed the immune effect of trivalent inactivated vaccine in different poultry species.The results showed that the qualification rate of H5 and H7 antibodies in broilers and layer hens was more than 98.21%,and the qualification rate in ducks was less than 5.45%,which may be related to the immune program of ducks.Among the farms that participated in the evaluation,only laying hens were immune with “Newcastle disease +H9（La Sota+H9 F strains）” inactivated vaccine,and H9 antibody was 98.52%.2.Isolation and identification of H9N2 avian influenza virusA strain H9N2 avian influenza virus was isolated from dead chicken from a commercial chicken farm in Linzi（named as: A/Chicken/Shandong/LZ/2019）,the respiratory and digestive tract damage were observed in sick chicken infected with the strain,and multiple organ dot hemorrhage.The biological characteristics of the isolate were evaluated,MDT and IPCI were118 h and 0.04 respectively,and the pathogenic to chicken embryos.The strain was the highest homology with “A（H9N2）/chicken/Guangxi/55/2005”,the homology of HA with vaccine strain “A/Chicken/Shanghai/F/98” HA was only 88.1%.The evolutionary relationship analysis showed that the vaccine strain and isolated strain is distant,the isolated strain belongs h9.4.2.5branch in the Eurasian lineage,and H9 F strain belongs to the H9.4.2.1 branch.This may be the cause of the sporadic occurrence of H9N2 subtype avian influenza in the poultry farm.In conclusion,the immunization efficacy of H5,H7 and H9 subtype avian influenza vaccines was evaluated in different poultry populations of the farms in Linzi District.The results showed that different poultry produced a large difference in antibody effect,meat ducks H5 and H7 antibody qualified rate was very low,only laying hens in the region were immune to the H9 subtype avian influenza vaccine.A H9N2 low pathogenic avian influenza virus was isolated from dead chicken in a farm in Linzi District,indicating sporadic epidemic of H9N2 avian influenza in the region,it is possible to relate to the vaccine strain used.This prompts us to better understand the avian influenza immunization situation and the prevalence state of H9N2 avian influenza in Linzi District,and provide a basis for the prevention and control of avian influenza.