Immunogenicity of Australian lentogenic strains of Newcastle disease virus

Seven-week-old chickens vaccinated oronasally with V4 and CT strains of Australian lentogenic strains of NDV were immune to intramuscular challenge with Herts 33 and Texas GB strains of virulent NDV. Vaccination of 1- and 3-week-old chickens with V4 strain by oronasal, conjunctival and drinking water routes using various doses of virus demonstrated that chickens were immune to oronasal challenge with Fontana 1083 strain of virulent NDV except where low doses of vaccine virus were administered. One 6- and 36-week-old chickens vaccinated oronasally with CT strain of virus remained immune to oronasal challenge with Fontana 1083 strain for 9 weeks after vaccination. Immunity was waning at 16 weeks after a single vaccination with CT strain.