Molecular Cloning of a Bangladeshi Strain of very Virulent Infectious Bursal Disease Virus of Chickens and its Adaptation in Tissue Culture by Site-Directed Mutagenesis

Abstract

Full-length cDNA of both genome segments of a Bangladeshi strain of very virulent infectious bursal disease virus (BD 3/99) were cloned in plasmid vectors along with the T7 promoter tagged to the 5'-ends Mutations were introduced in the cloned cDNA to bring about two amino acid exchanges (Q253H and A284T) in the capsid protein VP2 Transfection of primary chicken embryo fibroblast cells with RNA transcribed in vitro from the full-length cDNA resulted in the formation of mutant infectious virus particles that grow in tissue culture The pathogenicity of this molecularly-cloned, tissue-culture- adapted virus (BD-3tc) was tested in commercial chickens The parental wild-type strain, BD 3/99, was included for comparison The subclinical course of the disease and delayed bursal atrophy in BD-3tc-inoculated birds suggested that these amino acid substitutions made BD-3tc partially attenuated (author)