ISOLATION AND MOLECULAR CHARACTERIZATION OF VERY VIRULENT INFECTIOUS BURSAL DISEASE VIRUS (vvIBDV) ISOLATES FROM BACKYARD POULTRY IN ASSAM, INDIA
DOI:
https://doi.org/10.48165/abr.2026.28.01.37Keywords:
Assam, India, infectious bursal disease virus (IBDV), molecular characterization, Vero cells, VP2 geneAbstract
Infectious bursal disease (IBD), caused by the infectious bursal disease virus (IBDV), is a highly contagious viral infection of young chickens that causes immunosuppression and substantial economic losses in the poultry industry. This study aimed to isolate and characterize IBDV strains from backyard poultry in Assam, a major poultry-producing region of North-Eastern India. Cloacal swabs and bursal tissues were collected from chickens with clinical signs of IBD across four districts. Virus was isolated in chicken embryo fibroblast (CEF) cultures and propagated in Vero cells, and molecular characterization was performed by phylogenetic analysis of the VP2 gene. Affected flocks showed a cumulative mortality of approximately 5%, and viral titres reached 7.5 log₁₀ TCID₅₀ mL-1 by the 15th Vero-cell passage. Necropsy findings were consistent with IBDV, including haemorrhages in breast and thigh muscles, a hyperaemic cloacal bursa, a necrotic and hyperaemic liver, and enlarged spleen and kidneys. Phylogenetic analysis based on partial VP2 gene placed both isolates within the lineage of previously reported very virulent IBDV (vvIBDV) strains from India. These findings indicate that vvIBDV-related strains circulate among unvaccinated backyard poultry in Assam and may serve as candidate strains for future antigenic and vaccine-related investigations.
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