Vaccination of fowl with inactivated Newcastle disease vaccine by the respiratory route.

Chickens were vaccinated with inactivated Newcastle disease (ND) vaccine by the oculonasal, intratracheal (it) or the aerosol route and immunity was measured by determination of haemagglutinating inhibiting (HI) antibodies and survival following challenge. Dose-response to various vaccination schedules was studied in birds of various ages with or without maternal antibodies. IT application induced a stronger response than oculonasal application. A single application with a vaccine dose of 1 to 10 mg allantoic dry matter by the it or the aerosol route resulted in moderate titres in adult birds, while a dose of 0.1 mg still had a priming effect. In one-day-old SPF chicks doses of 1 to 10mg given with adjuvant induced only low titres but protection was present following challenge at 3 to 4 weeks of age, while 0.2 mg had no effect. Maternal antibodies interfered with vaccine efficacy. A more economical use of the vaccine and a better immune response was obtained by repeated vaccination. Twice weekly aerosol exposure, with a dose of about 0.2 mg, induced HI titres of 8 to 9 in 9-week-old hens after four exposures. Five aerosol vaccinations with doses of about 0.1 mg but with adjuvant were effective in young chicks with or without maternal antibodies. In SPF chicks HI titres of 8 to 9 were achieved, while broilers with high levels of maternal antibodies were protected completely against morbidity following challenge. It is concluded that, although repeated aerosol vaccination with inactivated ND virus is effective, it is not economical at present.