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PATHOGENICITY OF IBDV RELATED TO OUTBREAKS IN THE VACCINATED FLOCKS AND THE CAUSES OF VACCINATION FAILURE (Pages : 22 - 30)
M. N. ISLAM, S. M. H. RASHID, M. F. HOQUE, M. S. B. JULI AND M. KHATUNPathogenicity of infectious bursal disease virus (IBDV) related to the outbreaks in the vaccinated flocks and the probable causes of vaccination failure were field based investigated during March, 2007 to March, 2008 at Dinajpur district of Bangladesh. The virus was pathologically determined as very virulent infectious bursal disease virus (vvIBDV) and the probable causes of vaccination failure were identified. Among the 23 Gumboro incidences in the vaccinated flocks, 15 in broiler, 3 in layer and 5 in cockerel flocks were recorded during the course of observations. The number of the birds in the farms was variable ranging from 250-1250 and they were reared on litter. The flocks were divided into five groups basically based on the severity of the disease and the mortality patterns. A relationship between the mortality rate and bursal lesion scores was determined. One apparently normal and another one unvaccinated affected flocks were also included in this study for the comparison. The birds were vaccinated with commercially available Gumboro vaccines containing intermediate strains. The clinical signs of the affected birds of the vaccinated flocks were noted during the physical visit of the farms and the farmer’s complaints were also emphasized. The birds were examined systematically at necropsy and the lesions of the muscles and bursa of Fabricius were recorded. Only the bursae were collected, preserved at 10% formalin solution and processed for the histopathological study giving emphasis on bursal lesion scores. The pathogenicity of the virus related to vaccination failure was evaluated groupwise. The clinical signs of the affected birds were more or less similar to the signs generally developed due to the infection with vvIBDV, and clinically characterized as anorexia, high fever, whitish diarrhoea, dehydration, ruffled feathers, drowsiness and death. The morbidity of the affected flocks was around 100%, and the mortality rate was variable ranging from 7–38%. HigDownload