EFFICACY IN CHICKENS OF A HERPESVIRUS OF TURKEYS RECOMBINANT VACCINE CONTAINING THE FUSION GENE OF NEWCASTLE-DISEASE VIRUS - ONSET OF PROTECTION AND EFFECT OF MATERNAL ANTIBODIES

The onset of protection against Newcastle disease and the effect of ma ternal antibodies to Newcastle disease virus (NDV) and Marek's disease virus (MDV) on vaccine efficacy were determined following vaccination of chickens with a recombinant herpesvirus of turkeys (HVT) vaccine e xpressing the fusion (F) glycoprotein gene of NDV. Onset of protection following intra-abdominal administration of the recombinant HVT/F vac cine at 1 day of age and subsequent ocular challenge with the neurotro pic velogenic Texas GB strain of NDV was determined to occur between d ays 14 and 21 post-vaccination (PV). Vaccination with the Hitchner B1 strain of NDV resulted in protection by day 6 PV, and vaccination with an inactivated NDV oil-emulsion vaccine induced protection by day 14 PV. One-day-old broiler-type chickens with maternal antibodies to both NDV and MDV and 1-day-old specific-pathogen-free (SPF) white leghorn chickens lacking maternal antibodies were vaccinated with the recombin ant HVT/F vaccine or with control vaccines, challenged intra-abdominal ly with the very virulent RB1B strain of MDV on day 8 PV, and challeng ed with the Texas GB strain of NDV on day 29 PV. The HVT/F and NDV str ain Hitchner B1 vaccines provided 73% and 80% protection, respectively , against NDV in broilers, whereas both vaccines resulted in 100% prot ection in SPF leghorns.