MD was rst described in 1907 by the Hungarian veterinarian József Marek who observed polyneuritis signs along with histopathological lesions in the brain and peripheral nerves of chickens [5,6]. Following this rst conference report, the disease was noted in 1914 in the United States, the Netherlands, and Great Britain [1]. For many years, MD was sporadically observed among chickens and turkeys and was manifested by neurological signs and disorders of locomotor system [7]. A notable increase in mortality among commercial chickens was observed between 1920 and 1940. In the 1960s, the observed clinical signs were called by Dr. Biggs [8] as “Marek’s disease” but the observed clinical signs and lesions were misdiagnosed as lymphoid leukosis (LL). Therefore, MD

was assigned to avian leukosis group. The milestone in MD history was the description of clinical signs by Pappenheimer et al. [7] as lymphoproliferative lesions in the spatial ganglia and peripheral nerves. Subsequently, Churchill and Biggs [9] and Nazerian et al. [10] isolated an etiological agent that was herpesvirus and called it “Marek’s disease virus” (MDV). However, early attempt to reisolate the virus was not successful, probably due to the strictly cell-associated nature of MDV and the lack of specic-pathogen-free (SPF) chickens.