SCORING OF BURSAL LESIONS IN COMMERCIAL CHICKEN INFECTED WITH FIELD IBD VIRUS AT SYLHET REGION

Abstract

The current study was conducted to evaluate the pathogenicity and pathology of infectious bursal disease virus in commercial broiler chickens. A total of 45 bursa of Fabricius were collected from 9 commercial farm of different age (18-29 days) of different areas at Sylhet region. During necropsy both chickens and Bursa of Fabricius (BF) were weighed and examined for gross lesion and processed for histological investigations. Bursal Index and bursal lesion scoring were made to evaluate pathogenicity of the virus. The results showed that the weight of bursa increased effectively according to the body weight. According to the evaluation system 44.44% belongs to the bad category, 22.22% medium, 11.11% average and 22.22% excellent category. In post mortem examination there was severe hemorrhage present on BF, breast and thigh muscle. Hemorrhage was found at the junction between proventriculus and gizzard. Gelatinous and atrophied bursa was also found. Bursal lesion scoring was done based on histopathological investigations, the highest bursal lesion score was 4.6 ±0.40 that indicates bursal atrophy caused by very virulent strain. Bursa were characterized by atrophy, necrosis, fibroplasia, lymphoid depletion, cyst formation and infiltration of inflammatory cells. According to Bursal Index and the observed lesions of BF the virus causing infection of very virulent type. In conclusion, based on the results of the study most of the IBDV infected farms were affected with vvIBDV. However, virus isolation and determination of pathogenicity at laboratory are recommended.