1a.Objectives (from AD-416):
1. Evaluate antibody response induced by different Newcastle Disease virus (NDV) vaccine candidates expressing various gene inserts.
2. Evaluate efficacy of new NDV vaccine candidates against clinical disease and shedding after challenge with various velogenic NDV isolates.
3. Test different vaccination protocols for specific pathogen free (SPF) and commercial poultry to maximize NDV vaccine efficacies.
4. Share NDV challenge strains and reagents.
1b.Approach (from AD-416):
Different alternative Newcastle disease (ND) vaccines based on vector, reverse genetics or expression systems technologies will be generated and controlled for NDV gene expression by the Cooperator. Vaccines will be tested for immunogenicity and efficacy against different epidemiologically relevant NDV isolates. Protection will be evaluated in SPF and commercial chickens by prevention of illness and death, increasing resistance to infection, reduction in number of infected birds, decrease in the amount of challenge virus shed from respiratory and alimentary tracts, and reduction of transmission to contact birds. Different vaccine candidates will be associated in prime-boost immunization schemes to optimize immunity and protection.
This project is related to objective 3 of this in-house project: Develop vaccine strategies to effectively control Newcastle disease and stop disease outbreaks by developing vaccine platforms specifically designed to control low virulent and virulent Newcastle disease outbreaks.
Experiment #2 with 144 birds in 12 vaccine groups was completed. Swab samples were evaluated for amount of challenge virus shed and serum samples were evaluated for level neutralizing antibodies. Experiment #3 was completed with 12 vaccine groups and 564 swabs and 40 sera were evaluated. Both experiments tested various experimental Newcastle disease vaccines using either Herpes virus of turkey or Marek’s disease virus as a vector for expressing the Newcastle genes. There were two weeks between vaccination and challenge for experiment #2 and three weeks for experiment #3. While three weeks was better than two, there were still vaccines with decent protection with only two weeks before challenge. Because the F gene was used the pre-challenge hemagglutination-inhibition titers were not useful, but the post-challenge titers did correlate with the amount of virus shed from vaccinated birds, with birds shedding less virus having smaller post-challenge antibody titers.