Chickens are the most important natural host for Marek’s disease virus (MDV), cell-associated but readily transmitted alphaherpesvirus with lymphotropic properties of gammaherpesviruses. Marek’s disease is a highly contagious viral disease of poultry characterized by T-cell lymphomas and peripheral nerve enlargement. Marek’s disease is one of the most ubiquitous avian infections and is identified in chicken farms worldwide. Every flock, except for those maintained under strict pathogen-free conditions, is presumed to be infected. Marek’s disease readily transmitted among chickens. The virus matures into a fully infective, enveloped form in the epithelial cells of the feather follicle, from which it is released into the environment. It may survive for months in poultry house litter or dust. Dust or dander from infected chickens is particularly effective in transmission. Once the virus is introduced into a chicken flock, regardless of the vaccination status, infection spreads quickly from bird to bird. Infected chickens continue to be carriers for long periods and act as sources of MD virus. Shedding of infectious virus can be reduced, but not prevented, by prior vaccination. MDV not vertically transmitted. Although clinical cases are not always apparent, a subclinical signs as decrease in growth rate and in egg production, may be economically important. Currently available vaccines are considered as protective