Outbreak of Marek’s Disease in Chicken Flocks with Uncommon Pattern of Gross Lesions

Abstract

Marek’s disease is one of the highly contagious and oncogenic diseases of poultry that remains as a threat to the fast-growing poultry sector, even after proper vaccination. Generally, the disease is identified incidentally during the routine postmortem examination as nerve enlargement or as gross tumor lesions. The present article discusses the outbreak of Marek’s disease in three vaccinated commercial layer flocks with high mortality and subtle gross nodular lesions. Three to fivemonth- old, commercial layer chickens from three different farms were submitted for post mortem at Department of Veterinary Pathology, College of Veterinary and Animal Sciences, Pookode, Kerala with the history of weight loss and mortality rate of about 25 per cent. On postmortem examination, the carcasses revealed severe emaciation and atrophied to mildly enlarged visceral organs in the majority of cases except in three birds with small white nodules. Microscopical examination revealed, varying degrees of pleomorphic lymphoid cell proliferation in the liver, spleen, kidney, ovary, pancreas and thyroid. Polymerase chain reaction targeting gB gene confirmed the presence of Marek’s disease virus (MDV) in birds, with and without gross tumors. The birds from farms of different flock size showed similar high mortality rate but mostly without gross tumour lesions of MD. These findings emphasise the importance of histopathological examination in routine postmortem of chickens to identify diseases with gross nonspecific lesions.