The majority of carcasses will have lesions of the peripheral nerves, evidenced by enlargement and gray or yellow discoloration. The normal striated appearance of the nerve sheath is usually obliterated. Visceral Organs Tumors that infiltrate the visceral organs may be nodular or diffuse.
Nodular lesions have the typical appearance of focal tumor growths.
Many organs can become infiltrated by tumor cells including the ovary, heart, lung, kidney, liver, spleen, and others. Tumors involving visceral organs can occur without nerve lesions, especially in the acute form as described in the clinical signs section of this web page. Skin Lesions Lesions in the skin generally center around the feather follicles, and their severity varies from mild inflammation to severe proliferation that results in ulceration. This is particularly important when considering transmission , as the feathers and dander from these lesions can be infective. While lymphomatous invasion of nervous tissue and visceral organs are very typical of Marek's disease infection, gross evidence of such lesions along with clinical signs cannot by themselves be a definitive diagnosis.