Resistance of the respiratory tract of the chicken to Newcastle disease virus infection following vaccination: The effect of passively acquired antibody on its development

Vaccination of chickens with a live Newcastle disease virus (NDV) vaccine given intranasally or intramuscularly or an inactivated NDV vaccine given by the respiratory route induced variable degrees of resistance in the respiratory tract to challenge with an avirulent strain of NDV. An inactivated NDV vaccine given intramuscularly, however, induced little resistance, despite the high concentration of serum antibody that developed. When a live NDV vaccine was given to chicks with passively acquired antibody, serum antibody response was markedly inhibited, but no comparable inhibition of respiratory tract resistance could be demonstrated. The results suggest that the direct or indirect exposure of the respiratory tract tissues to viral antigen was necessary for the induction of resistance to infection in the respiratory tract.