Studies on the development of pelleted Newcastle disease virus (NDV) vaccine.

White leghorn chickens (7-10 weeks old) were orally infused with varied doses of lentogenic and mesogenic strains of Newcastle disease virus. The antibody response of the chickens was monitored by haemagglutination inhibition tests weekly for 4 weeks postinfusion. A high dose of virus (10(9) EID50) was necessary to induce a serological response typical of chickens that resist challenge.

Thermostability of the hemagglutinin of Newcastle disease virus as a strain marker in epizootiologic studies.

The recent isolation of viscerotropic velogenic strains of Newcastle disease virus having a thermosensitive hemagglutinin and of a lentogenic strain with an unusually thermostable hemagglutinin confirmed that virulence for chickens was not related to the thermostability and could be used as a marker for strains in epizootiologic investigations.

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.