Virus-neutralizing antibody in sera and secretions of the upper and lower respiratory tract of chickens inoculated with live and inactivated Newcastle disease virus

The appearance of virus-neutralizing antibody in nasal, tracheal and lung secretions as well as in sera of chickens inoculated with liver and inactivated Newcastle disease virus (NDV) was studied. Antibody in tracheal secretions was most effectively induced by the administration of live or inactivated virus directly into the respiratory tract whereas antibody in lung secretions was best stimulated by live virus administered intramuscularly. Antibody appeared in tracheal secretions at 6 days after intranasal infection with NDV but then declined in titre, whereas antibody did not appear in nasal secretions until 8 days after infection but then proved to be more persistent. Only live vaccine virus administered by the respiratory route was successful in stimulating antibody in all secretions examined as well as in the serum.