RAMA DEVI, V (Major)ANNAPURNA, PLAKSHMI KAVITHA, KSRIKANTH, K.V2017-08-192017-08-192016-11http://krishikosh.egranth.ac.in/handle/1/5810029037THESESABSTRACT: Marek’s disease (MD) is a lymphoproliferative disease of chickens caused by Marek’s disease virus (MDV-1). Of late, there are incidences of MD in vaccinated commercial layer chicken in India, causing severe economic losses. Only a few reports are available about the status of the disease in Andhra Pradesh. Hence, keeping this in view the present work was undertaken to study the incidence and gross and histopathological lesions in various organs along with diagnosis of MD by PCR technique. The materials for the present study were procured from Nuzividu, Tanuku and Anaparthy towns, private diagnostic laboratories,Vijayawada and from the post mortems conducted at Department of Veterinary Pathology, NTR College of Veterinary Science, Gannavaram. The duration of the study lasted from December 2015 to October 2016. A total of 520 dead layer birds that were vaccinated previously against the disease were examined in detail and representative samples from suspected MD cases were collected. Of these, 58 birds (11.15%) of 20-52 weeks of age were found positive for MD based on clinical signs, gross and histopathological findings in different organs and by PCR diagnosis.The MD affected chicken exhibited clinical signs of emaciation, weight loss, paleness of comb, marked reduction in egg production, ruffled feathers, diarrhoea, lameness and prostration before death.Out of 58 MD cases, visceral tumors of acute form of MD were noticed frequently in the liver (93.1%), kidney (79.3%), spleen (53.5%) and ovaries (20.7%) and less frequently in the proventriculus (17.2%), intestines (13.8%), skin (10.3%), heart (5.2%) and lungs (5.2%).Grossly, the livers were enlarged and had multiple greyish-yellow tumor nodules of either diffuse, nodular or of miliary form. The kidneys were enlarged, irregular and pale and had pinpoint to a few mm greyish white nodules or masses in many cases. The spleen was enlarged and had miliary greyish white lymphomas. The ovaries were enlarged, irregular, pale or greyish white and revealed firm tumorous mass with cauliflower like appearance. The mucosa of proventriculus and the intestinal wall were thickened and nodular tumors were visible through serosa of intestine. Greyish white feather follicular nodules in the skin, greyish white nodular growths in the myocardium and in the lungs were found.Histologically, in the MD affected organs lymphoproliferative lesions were noticed with infiltration of pleomorphic lymphoid cells and the severity of visceral lymphoid lesions were graded into mild, moderate and severe. The sections of liver in severe cases, revealed diffuse or massive proliferation of pleomorphic lymphoid cells or nodular lymphomas compressing the surrounding parenchyma.In severe cases, diffuse proliferation and infiltration of pleomorphic lymphoid cells, plasma cells and a few MD cells or discrete large lymphomas were noticed compressing the renal parenchyma in the kidneys. In severe cases, spleen revealed proliferation and infiltration of lymphoblasts, small and large lymphocytes, macrophages and reticular cells or multiple or solitary lymphomas in the parenchyma. The lesions in the ovaries were characterized by diffuse pleomorphic lymphoid cell infiltration around the ovarian follicles with distortion of ovarian structure in severe cases.In the proventriculus, diffuse infiltration of pleomorphic lymphoid cells in the mucosa, submucosa and within and in between the glands and in the serosa were evident in severe cases. Marked pleomorphic lymphoid cell proliferation was frequently observed in the mucosa, submucosa, muscle layers and subserosa of intestine and lymphomas with nodular aggregation of large and small lymphocytes were clearly evident in the serosa. The lesions in the skin in moderate cases were characterized by nodular infiltration of pleomorphic lymphoid cells below the epidermis, in the dermis and around the feather follicles. In the myocardium, focal degeneration of muscle fibres, proliferation and infiltration of pleomorphic lymphoid cells and rupture of cardiac muscle fibre bundles were seen. The lung sections showed congestion and marked infiltration of pleomorphic lymphoid cells in the wall of the air capillaries and around the secondary bronchus and parabronchus. The sciatic nerve revealed type A lesions in two birds. In the present study, PCR was carried out for the detection of 132 bp repeats and meq gene of serotype 1 MDV in the tumor tissue samples of MD suspected birds that produced two tandem repeats of 132 bp and the primers specific to meq gene produced an expected size of amplicon in MD positive birds. In the present investigation, the pathological and molecular diagnosis of MD was carried out in commercial layer chicken. It was evident that in spite of vaccination, MD continues to be a major threat causing significant losses in commercial poultry flocks.ennullThesis