1 - Introduction

Abstract

This chapter outlines the historical background of Marek's disease (MD). The acute lymphoid form of MD became serious with the expansion and intensification of poultry production in the 1960s. Marek's disease herpesvirus (MDV) was identified as the causative agent of this disease. MDV is a lymphotrophic herpesvirus that induces T-cell lymphomas in the chicken (its natural host) after an early cytolytic infection. Stress is the most important environmental factor that plays a major role in MD. The 1960s was a period of intense research on Marek's disease, and funds were made available to provide isolation facilities and strains of chicken that were susceptible to the disease. The introduction of vaccination in the 1970s was a major breakthrough. The problems of morbidity and mortality because of MD receded, but vaccine breaks began to be reported. As a result, increased virulence of challenge viruses occurred within 10 years. The subsequent introduction of more aggressive vaccines and vaccine regimes has driven MDV to evolve to even greater virulence over the past decades. Further studies are required to obtain robust scientific evidence and more sustainable vaccination strategies for MDV infection.