Marek’s disease (MD) causes paralysis and tumours in chickens. Caused by serotype 1 strains of the Marek’s disease virus (MDV-1) which is shed from skin of infected chickens, persists for many months in dust in contaminated poultry houses, and spreads to other chickens by inhalation, MD is a major disease affecting poultry health, welfare, and productivity. It is endemic in UK poultry but is effectively controlled by live vaccine viruses, which are harmless relatives of MDV-1, and include CVI988, HVT, and MDV serotype 2 (MDV-2). MDV-2 vaccines are widely used in the Americas and Asia but not in the UK. However, by testing samples collected from poultry farms, we found MDV-2 is widespread in the UK, circulating freely and naturally in flocks, persisting long-term at high levels, and co-infecting with MDV-1 and HVT and CVI988.

However, little is known about these MDV-2 strains.  We would like to know whether they affect flock health and disease, and production parameters such as egg production and mortality, and whether they could be used as effective recombinant vaccines against MD and other poultry diseases. In partnership with poultry industry vets, we will perform a longitudinal study in broiler-breeder and layer chicken flocks to collect data on flock health and productivity, and investigate the kinetics of MDV-2 infection, shedding, and transmission, and the frequency of co-infection with MDV-1 field strains and vaccine viruses. We will use sequencing to determine variability of MDV-2 strains and will study the characteristics of selected MDV-2 strains by growing these viruses in cell culture then using them to infect chickens under controlled laboratory conditions to examine replication, persistence, clinical signs and transmission. Most MDV-2 strains have characteristics which make them suitable as vaccines against MD: they do not cause disease, they grow well in the chicken and persist for many months, and they are easily transmitted between chickens to maintain a high level of exposure of the flock to vaccine virus. We will engineer a selected MDV-2 field strain to create a recombinant multivalent vaccine virus, then test its ability to protect chickens against MD, infectious bursal disease and Newcastle disease under controlled laboratory conditions.

Contact details:

Dr Yongxiu Yao

Group Leader in Molecular Biology, Molecular Virology, Viral Diseases, Virology

The Pirbright Institute