Influence of vaccination with avirulent herpesvirus on subsequent infection of chickens with virulent Marek's disease herpesvirus.

Vaccination of chickens with turkey herpesvirus (HVT) or attenuated Marek's disease herpesvirus (aMDHV) blocked infection with virulent MDHV (VMDHV) for approximately 5 weeks after contact exposure. However, there was no apparent blockage of infection when challenge virus was administered intraabdominally (IA). Evidence for infection with VMDHV was based on viral isolation by in vivo assay or by detecting precipitins to "A" antigen associated with virulent virus. The HVT stimulated production of neutralizing antibody against VMDHV in a high percentage of chickens, whereas the aMDHV was a comparatively poor inducer of such antibody. Despite this difference, both of the vaccinal viruses conferred protection against development of Marek's disease.