8-Marek’s Disease: It is one of the most common and well-studied diseases of young chickens. Etiology: Cell-associated herpesvirus.
Pathogenesis: virus replicates in feather follicle-epithelium, infection through respiratory route, viremia, infection of B cells, cytolysis, infection of activated T cells, cytolysis, immunosuppression, infection of other organs like nerves (paralysis & blindness), latency, transformation of T cells (CD4), lymphoma. The disease includes 4 syndromes: 1-Neural Syndrome 3-Cutaneous Syndrome
2-Ocular Syndrome(Gray eye disease) 4-Acute Marek’s Syndrome
Lesions: Gross: i-Bursal and thymic atrophy. ii-Swollen , thickened and beaded peripheral nerves. iii-Enlarged organs with pale white tumors in liver, spleen, kidneys, lungs, proventriculus, iv-intestine, heart, gonads and thymus. v-Irregular, grayish-white iris. vi-Prominent feather follicles and skin ulceration.