Genetically engineered cell culture adapted infectious bursal disease virus (IBDV) mutants

A method for the preparation of an infectious IBDV mutant which will replicate in CEF cell culture, comprising:

• (i) separately preparing a DNA construct comprising cDNA of genome segments A and B of an IBDV which is not capable of replication in CEF cell culture,
• (ii) introducing a mutation in:
• (a) one or more codons of the VP2 gene encoding an amino acid at positions 253 and 284 of a Variant-E or Classical IBDV strain, or in
• (b) a codon of the VP2 gene encoding an amino acid at position 284 of a GLS IBDV strain,
• on the cDNA comprising the segment A,
• wherein the codons of the VP2 gene encoding amino acids at positions 253 and 284 encode a histidine and threonine, respectively, in the case of a Variant-E or Classical IBDV strain, or
• wherein, the codon encoding the amino acid at position 284 of the mutated VP2 gene encodes a threonine in the case of a GLS IBDV strain,
• (iii) allowing RNA transcripts of the cDNA comprising the segment A and the segment B to initiate replication of the IBDV mutant in host cells in a culture medium, and
• (iv) isolating the IBDV mutant from the culture.