Prevalence, Gross Pathology, and Histopathology of Marek s Disease in Backyard Chickens in Northeastern Tunisia

Marek's disease (MD) is a common worldwide lymphomatous and neuropathic disease of chickens. Infection can cause significant losses in chicken production due to high mortality and morbidity. The present study aimed to determine the prevalence of MD in backyard flocks in the Grand-Tunis region of northeastern Tunisia and to analyze clinical cases over an eight-year and three-month period, from September 2012 to December 2020. A total of 798 cases were received for necropsy examination in the avian clinic of the National School of Veterinary Medicine of Sidi Thabet, Tunisia. Among these, chicks suspected of having MD underwent clinical observation, postmortem examination, and histopathological analysis. The results showed that 61 chickens (7.64%) were suspected to have MD. Clinical and postmortem examinations revealed different forms of MD including visceral (31 cases), mixed (20 cases), and nervous forms (10 cases). Postmortem examinations showed two types of lesions including hypertrophy and lymphomatous tumors. The highest frequencies of lesions were noted in the liver (74%), spleen (62%), sciatic nerves (48%), lungs (36%), and kidneys (31%). Hypertrophy predominated in the spleen (49%), sciatic nerves (48%), liver (28%), kidneys (25%), lungs (21%), proventriculus (18%), and gonads (17%). Conversely, lymphomatous tumors were more frequently observed in the liver (46%), heart (23%), lungs (15%), and spleen (13%). Histopathological investigations revealed pleomorphic infiltrations with lymphocytes and plasmocytes in visceral organs, sciatic nerves, and the skin. High histological scores were recorded in the liver, spleen, lungs, kidneys, and heart. The current study confirmed endemic MD in backyard chicken populations in Grand-Tunis région and confirmed that it can be a serious threat to poultry health in the study area.