ABSTRACT
Marek's diseases is a contagious disease affected chicken over all the world there are four different form of it and the infected birds may exhibit one or more from ( cutaneous ,visceral , ocular &neural) forms. MDV caused by infection of lymphocytes by Gallid alphherpesvirus 2,vaccines have been used successfully in many nations to control and stop the spread of the disease ,recent data indicates that vaccines effectiveness is declining now as a result of viral evolution .The current work was conducted from (July- November)of 2022 to diagnoses MD in a 20 naturally infected chicken from a total out 50 chicken which randomly received from different regions to the veterinary teaching hospital. Recent study research showed the present of gross and histopathological lesions of MDV infection represented by (2,4% in liver,1,6%in lung &kidney respectively,1,2% leg paralysis,0,8% in brain & finally spleen lesion was 0,4%) .The gross lesion characterized by hemorrhage ,congestion , splenomegaly, nodular lesion of liver & sprain of leg nerve , on the other hand the Histopathological lesions represented by congestion, degeneration& necrosis of hepatocytes , infiltration of monocular cell, vasogenic edema and spongy from cell inside brain tissue ,cell swelling and hyaline cast of renal tubules & lymphoproliferative foci with different size inside spleen parenchyma. From our result we conclude the occurrences of MDV in backyard chicken in different region of Mosul city