Features of the Manifestation of Marek's Disease in Poultry Farms of the Rostov Region, Russian Federation

The authors carried out monitoring studies to examine the epizootic process features and the manifestation of clinical signs and pathological changes in Marek's disease in various poultry farms in the Rostov region. The disease was most often in chickens aged 1.5 to 6 months. Two forms of the disease were registered: classical (nervous) - 63.3% of cases, and tumor (visceral) - 36.7% of cases. There was an unequal manifestation of symptoms of the disease, because of the different state of natural resistance and immunological reactivity of sick birds. The main clinical signs of Marek's disease in chickens included: oppression; loss of appetite; development of paresis and paralysis; violation of movement coordination; cachexia; anemic crest, earrings and visible mucous membranes; change in the shape and constriction of the pupil; depigmentation of the iris of the eyes; partial or complete loss of vision; lameness; damage to the feather follicles; and the formation of tumors on the skin. The mortality rate of birds with nervous lesions was 70%. The surviving birds died within 1–2 months from the development of neoplastic changes in the internal organs. The main pathological changes in Marek's disease were thickening and destructive changes in nerve fibers; and neoplastic changes in the parenchymal organs, lungs, intestinal mesentery, gastrointestinal tract, muscle tissue and skin. Most often, the disease was registered in the personal subsidiary plots of citizens. It manifested itself in massive epizootic outbreaks, usually in a nervous form with a high morbidity and mortality. In poultry farms, the disease was recorded extremely rarely. As a rule, it manifested itself in a tumor-like form, in isolated cases among a small percentage of poultry. Keywords: poultry, chickens, Marek's disease, clinical signs, pathological change