Screening Of Adjuvants For Trivalent Inactivated Vaccine Based On The APEC Lipopolysaccharide Deficient Mutants And Preliminary Study On Immune Duration Of The Vaccine

Avian pathogenic Escherichia coli(APEC)can cause a variety of extraintestinal diseases such as pericarditis,air sacculitis,perihepatitis,cellulitis and sepsis in poultry,resulting in high morbidity and mortaliy,leading to serious losses to the poultry industryIn this study,the APEC lipopolysaccharide(LPS)deficient strains E516?lpxL?lpxM(01 serotype),E058?loxL?lpxM(O2 serotype)and E522?lpxL?lpxM(078 serotype)previously constructed in our laboratory were mixed as the vaccine antigens.The corresponding trivalent inactivated vaccine was emulsified with white oil adjuvant Total 170,white oil adjuvant Marc52 and aluminum gel adjuvant respectively.The safety and immunological efficacy of the three vaccines were assessed to screen the optimal adjuvant of trivalent inactivated vaccine.After the vaccine adjuvant was determined,we studied the duration of immunization of the trivalent vaccine.The results of the study are as follows:1.Safety comparison between the APEC trivalent vaccines with different adjuvantsThe trivalent vaccines formulated with three different adjuvants were used to inoculate 14-day SPF chickens at a dose of either 0.5 mL/bird or 1.0 mL/bird for vaccine safety assessment.The results showed that the chickens inoculated with white oil adjuvant inactivated vaccines at the dose of 0.5 mL/bird,some chickens appeared temporary depression between 12 and 24 hours after vaccination,vaccinated chickens had no clinical signs thereafter.The chickens vaccinated at the dose of 1.0 mL/bird showed retardation between 5 and 8 hours post vaccination,and returned to normal within 24 hours.Due to the large dose(1.0 mL/bird),some chickens showed nodules ranging in size from 0.1 to 1.2 cm at the injection sites,but no systemic adverse symptoms were observed.The nodules at the injection site gradually disappeared within one week,and the chickens recovered.The chickens injected with the aluminum gel adjuvant inactivated vaccines experienced normal throughout the whole-observation period,and no abnormalities were found at the injection site.The above results showed that the vaccines developed in this study were safe.2.Immunological efficacy of the APEC trivalent vaccines with different adjuvantsThe 14-day SPF chickens were immunized with three vaccines mentioned above respectively,and challenged with the parental strains E516(OI serotype),E058(02 serotype)and E522(078 serotype)at 42 days of age.The results showed that the survival ratios of birds in the white oil adjuvant Total 170 vaccine group were consistent,7/10,and the survival ratios of birds in the white oil adjuvant Marc52 vaccine group were 5/10,5/10 and 7/10 respectively.The survival ratios of birds in the aluminum-adhesive adjuvant vaccine group were 3/10,3/10 and 5/10,and the mortality of birds in all three challenge control groups was 10/10 consistently.The above results showed that the aluminum-gel adjuvant vaccine had a poor efficacy in birds against wild-type strain challenge,whereas white oil adjuvant Total 170 and white oil adjuvant Marc52 vaccine,especially the former could have a sound efficacy.As a result of the safety and efficacy assessment,the white oil adjuvant Total 170 was chosen as the prototype vaccine adjuvant.3.Immune duration of the APEC LPS-deficient trivalent inactivated vaccineIn this study,14-day SPF chickens were immunized with APEC LPS-deficient trivalent inactivated vaccine,and then challenged with the parental wide type strains on the 30th,60th and 90th day after vaccination.The efficacy,specific antibody levels and histopathological changes in chicken visceral tissue were evaluated.The results showed that chickens were well protected on the 30th,60th and 90th day post-vaccination from parental strain challenge.Due to the reduced susceptibility of adult chickens to APEC,the decline in deaths of the chickens on 90-day post-vaccination challenged with parental strains was reasonable.The life span of commercial broilers is generally less than 9 weeks.The commercial broilers could be effectively protected by a single vaccination with the prototype trivalent inactivated vaccine.Considering a variety of factors,we tentatively set the immune duration of the APEC LPS-deficient trivalent inactivated vaccine as 3 months.