Comparison of Marek?s Disease Virus Challenge Strains and Evaluation of Interference Using Hvt Vector Vaccines

The first objective is to compare multiple virulent Marek's disease virus (vMDV) challenge strains in both vaccinated and unvaccinated birds to determine an optimal challenge strain for satisfying USDA licensing requirements for turkey herpesvirus (HVT) standard and HVT vector vaccines. The results will be useful to vaccine companies that require minimum morbidity levels to be met for valid immunogenicity trials. The second objective of this study is to evaluate interference of commercial HVT vector vaccines, an issue that perhaps is just now coming to light as multiple types of very similar vaccines are being mixed together for the first time.