Successful control of Marek's disease by vaccination.

Marek's disease (MD) is a neoplastic disease of poultry caused by the highly contagious Marek's disease virus (MDV). Vaccination with live attenuated vaccines forms the cornerstone of the current MD control programmes. The widespread use of the vaccines in the last 30 years has significantly reduced the losses from MD. Despite the huge success of the vaccination policy, the continuing trend in virulence increase of field strains of MDV has forced the introduction of new generations of vaccines to keep up with the creeping virulence increase of MDV. In these circumstances, it is very important to undertake research to develop more sustainable strategies of control. Development of new recombinant DNA technologies such as the use of bacterial artificial chromosomes (BAC) offers the possibility of developing molecularly-defined vaccines. In addition, the availability of the whole chicken genome sequence allows the opportunity of exploiting genetic resistance against MD as another sustainable strategy.