An outbreak of Marek’s Disease in a Commercial Poultry Farm in Naththandiya, Sri Lanka: A Case Study

Introduction: Marek’s disease (MD) is a major threat to the poultry industry worldwide and significantly affects production and economic stability. In this context, an outbreak in a commercial poultry farm in Naththandiya, Sri Lanka, served as a crucial alarm to avian health management. The clinical signs found during this outbreak not only highlight the virulence of MD virus but also raise questions regarding the effectiveness of the current control measures. Case report: The outbreak was found in a commercial poultry farm with 4500 Brown Leghorn female chickens including 2500 of 14 weeks old chickens, and 2000 of 6 weeks old chickens in Naththandiya, which was characterized by marked mortalities of 15-20 chickens/day in elder chickens and 35-40 chickens/day in 6 weeks old chickens. The older chickens have been vaccinated with the oral Infectious Bursal Disease (IBD) vaccine at 3 weeks and 11 weeks of age and also with Fowl Pox vaccine at 8 weeks of age. The younger chickens have been given only IBD vaccine at 3 weeks of age. The outbreak showed a wide range of clinical signs, including swollen and closed eyes, nasal discharge, respiratory distress, and anorexia. The post-mortem examination revealed pathognomonic lesions such as grey-white foci of neoplastic tissue in the liver, lungs, and kidneys, enlargement of the sciatic nerve with loss of cross striations, visceral organ enlargement such as liver, kidney, and spleen which indicates the presence of MD virus along with secondary infections caused by Escherichia coli (E. coli). Histopathological examination and bacterial culture confirmed the MD and E. coli infections respectively. Conclusion: This outbreak highlights the importance of vigilant surveillance, proactive management, and continuous review of vaccination protocols to control the transmission of Marek’s disease effectively.