Sequence comparisons of a highly virulent infectious bursal disease virus prevalent in Japan.

Variable cDNA regions in the VP2 gene of five highly virulent infectious bursal disease viruses (IBDVs) isolated in Japan were amplified by polymerase chain reaction (PCR) and sequenced. The nucleotide sequences of five highly virulent IBDVs were identical. Comparisons of the nucleotide and the deduced amino acid sequences with those of other strains of IBDV indicated that Japanese highly virulent IBDV is different from all other strains of IBDV that were compared. The number of amino acids that differed between strains (substitution score) showed that highly virulent IBDV is more closely related to European virulent strain 52/70 than to Japanese conventional strains. These results strongly suggest that a single strain of highly virulent IBDV that might have originated from a European strain is prevalent in Japan.