Immunological properties of inactivated vaccines against Newcastle disease based on virus antigens VII and II the genotype

Abstract

Newcastle disease (ND) is now widely spread in many countries of Eurasia, Africa and the Americas and causes significant economic damage to poultry farming. New NDinfected localities are reported in the Russian Federation every year; besides, the number of farms with vaccinated poultry demonstrating high specific antibody titres, decreased performance and survivability while being asymptomatic has increased. This is attributed to the virus evolution leading to the emergence of new genotypes represented by highly virulent strains. Since 2019, subgenotype VII-L has been isolated from Newcastle disease outbreaks in Russia. The vaccines currently available on the market do not confer appropriate protection against it due to the lack of antigenic matching between vaccine strains and this subgenotype. The development of a vaccine based on subgenotype VII -L will allow to ensure protection of poultry flocks against Newcastle disease caused by new NDV isolates. The immunological properties of emulsion inactivated vaccine against Newcastle disease based on genotype VII NDV (ARRIAH G7 strain) antigen were studied in 30-day-old Hisex Brown chickens. A similar vaccine based on genotype II NDV LaSota strain antigen was used as control. Tests of different immunizing antigen doses were carried out. The vaccines were tested for induced humoral immunity level (HI antibody titres), as well as for protective effect (protective index) after challenge with a highly virulent genotype VII NDV strain. The tests revealed that the antigenic activity and protective effect of both vaccines depended on the antigen concentration in the inoculation volume. Antibody titres were always higher when homologous antigens were used in HI tests. The vaccine based on the antigen of ARRIAH G7 strain (homologous to the challenge strain) was more effective than the control vaccine. Less ARRIAH G7 strain antigen was required to protect 50% of vaccinated poultry, compared with LaSota strain antigen. The comparative assessment of the same doses of the antigens showed that the vaccine based on ARRIAH G7 strain antigen had better immunological properties. The tested antigens demonstrated 18.3% bilateral affinity.