PATHOLOGICAL AND MOLECULAR DIAGNOSIS OF INFECTIOUS BURSAL DISEASE IN COMMERCIAL CHICKEN
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Date
2022-03
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SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI - 517 502. (A.P.) INDIA
Abstract
The present study was undertaken to know the occurrence of IBD in commercial
chicken in around Vijayawada and to carry out pathological and molecular diagnosis of
IBD. In the present study, a total of 922 IBD suspected birds of 4 to 6 weeks age were
procured from different places in and around Vijayawada, from private diagnostic
laboratories besides postmortems conducted in NTR College of Veterinary Science,
Gannavaram. At necropsy, IBD was diagnosed in 252 birds out of 922 screened with an
overall occurrence of 27.33% based on pathological lesions and molecular detection of
IBDV by RT-PCR.
The disease was more prevalent in 4 to 6 weeks aged birds with majority of
cases occurring during the 5th week (40.11%). The occurrence was highest in April to
September months (31 to 40%). As per the history, the affected birds showed
depression, watery diarrhoea (white to yellowish), soiled vents, anorexia, ruffled
feathers, reluctance to move, closed eyes and death.
Necropsy conducted in 252 birds revealed predominant gross lesions in the bursa of
Fabricius, spleen, thymus, caecal tonsils. Petechiae and ecchymoses on the pectoral and
thigh muscles, haemorrhages at the proventriculus-gizzard junction. Bursa was swollen
and oedematous with creamy or yellowish discoloration, gelatinous exudates in the
serosa, congestion and haemorrhages on the serosal and mucosal surfaces and inner
surface of longitudinal laminae in almost all the cases. Occasionally, the bursa became
atrophied and whitish or creamy, which sometimes contained cheesy mass in the lumen.
The spleen was enlarged and mottled. Kidneys were markedly swollen, congested and
liver was enlarged, friable and yellowish in few cases.
Histopathology revealed the prominent findings in bursa of Fabricius,
characterized by congestion and hemorrhages along with lymphoid depletion of various
degrees in the follicles resulting in atrophy of follicles and formation of cystic spaces
within the follicles. Presence of eosinophilic necrotic material in the bursal follicles
along with degenerating heterophils, atrophy of plicae, widening of interfollicular
spaces with proliferation of fibrous connective tissue and sloughing of bursal epithelium
was observed in few cases.
Microscopic examination of spleen depicted congestion of splenic vessels and
sinusoids, depletion of lymphocytes of varying degrees in white pulp and germinal
centers. Thymus revealed decrease in thymocyte density in the cortex and congestion in
most of the cases. However, in some cases disruption of normal architecture of cortex
and medulla was also evident. Lymphoid depletion in lymphoid nodules, mucosal
necrosis along with infiltration of mononuclear cells in the lamina propria were noticed
in caecal tonsils in majority of the cases.
Kidneys revealed interstitial haemorrhages and congestion in peritubular
capillaries, severe infiltration of inflammatory cells, degeneration and individualization
of tubular epithelial cells with detachment from the basement membrane and glomerular
shrinkage. Liver revealed haemorrhage and severe necrosis of hepatocytes, congestion
in the central vein, fatty change in hepatic parenchyma, diffuse coagulative necrosis of
hepatocytes, along with severe infiltration of mononuclear cells in the portal areas of the
liver. In the present study, pooled bursal samples were collected from 33 birds and
utilized for molecular diagnosis of by RT-PCR using specific primers targeting VP2
gene of IBDV. Electrophoretic analysis revealed an amplified product of 480 bp
fragment of VP2 gene in 9 samples thus confirming the presence of IBDV.
The nucleotide sequencing and phylogenetic analysis of present IBDV sample
(OM2024620) revealed it’s close relation with the strains of Kerala (MK 861022.1),
Gujarat (AB605259.1), Karnataka (EU788042.1) and Haryana (AY739668.1).
In the present study, the pathological and molecular diagnosis of IBD was
carried out and the occurrence of IBD in commercial chicken in and around Vijayawada
was recorded. It was evident that IBD continues to be a major threat causing economic
losses in chicken in the study area
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