Marek's disease (MD) is a lymphoproliferative
viral disease of chickens, which has been controlled through vaccination since 1969. MD
vaccines protect against
tumors but do not provide sterilizing immunity, and thus it is generally believed that their use has contributed to increase virulence of field strains with the ability to cause MD in vaccinated chickens. Traditional methods of developing
vaccines, like cell culture attenuation, have proved unsuccessful for the development of improved
vaccines to protect against highly virulent MD virus (MDV) field strains. With the advent of
recombinant DNA technology, it is now possible to study MDV gene function and develop rational
vaccines that protect against highly pathogenic strains. In addition, the long term protection conferred by MD
vaccines, their excellent safety profile, their efficacy when administered early (at hatch or in ovo), and their ability to overcome maternal
antibodies, has made MDV an excellent candidate vector to protect not only against MD but also against other important viral
poultry diseases. In this review we will discuss the current status of MD
vaccines and their use as vector
vaccines to control important viral
poultry diseases.