Marek disease

a lymphoproliferative disease of chickens, formerly included in the avian leukosis complex but now known to be caused by either of two viruses known as gallid herpesviruses 2 and 3. Lymphoid cell infiltrations are usually in the peripheral nerves and gonads but may also be found in visceral organs, skin, muscle, and the iris; there may be perivascular cuffing of blood vessels in the central nervous system. Where lesions are dictates the clinical signs, such as paralysis or blindness. When there are mainly neurological symptoms, it is called fowl or range paralysis or neural lymphomatosis. When there are mainly ocular symptoms, it is called ocular lymphomatosis, and with mainly skin symptoms it is called skin leukosis.