Efficacy of Rispens CV1988 Vaccine Against Challenge with Marek's Disease Viruses of Varying Virulence, Effects on Viral Kinetics and Field Application of a Rispens Specific qPCR Test

Abstract

Marek's disease (MD) is an economically important poultry disease, which is successfully controlled by imperfect vaccines. The imperfect vaccines for MD, herpesvirus of turkeys (HVT) and HVT/Gallid herpesvirus 3 (GaHV-3) (bivalent) are likely to have contributed to the observed increase in virulence which has led to sequential failure of these vaccines in some parts of the world. The Gallid herpesvirus 2 (GaHV-2, MDV-1) Rispens CVI988 vaccine, first developed in 1972, has not been affected by this failure and is considered to be the gold standard Marek's disease vaccine, being widely used worldwide to vaccinate long lived layers and breeders. Two experiments were designed to investigate this vaccine and its efficacy in Australia. An experiment in isolators investigated the protection provided by Rispens vaccine against Australian pathogenic GaHV-2 isolates of varying virulence (virulent, vMDV and very virulent vvMDV), and the kinetics of viral genome copy number of Rispens and the pathogenic MDV isolates in single and mixed infections. In the second experiment, a Rispens virus specific qPCR test was used to measure the vaccine take in invasive and non-invasive samples and the long-term viral kinetics of the Rispens virus in the field. Co-infection levels of Rispens and pathogenic GaHV-2 in the field and the possibility of establishment of Rispens virus in unvaccinated broiler flocks were also examined. Experiment one used 236 commercial ISA Brown chickens having maternal antibody directed against Rispens vaccine in 12 isolators. Chicks were vaccinated or not vaccinated with Rispens vaccine at hatch and challenged with vMDV isolate MPF57, vvMDV isolate FT158 at 5 days of age or left unchallenged. Each of the six treatment combinations was replicated in two positive pressure isolators.