PATHOLOGICAL AND MOLECULAR DIAGNOSIS OF MAREK’S DISEASE IN COMMERCIAL LAYER CHICKEN
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Date
2016-11
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SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI – 517 502. (A.P) INDIA
Abstract
ABSTRACT:
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.
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