Very virulent infectious bursal disease virus isolated from wild birds in Korea: epidemiological implications

To explore the epidemiological link between infectious bursal disease virus (IBDV) in wild birds and domestic chickens in Korea, we examined 107 free-living wild birds, representing 7 species, that were found dead of apparent natural causes in Korea over the past two years for the presence of IBDV. Five birds were tested positive for IBDV by RT-PCR assay: black-billed magpie (n=1), mallard duck (n=2), bean goose (n=1) and white-fronted goose (n=1). IBDV was isolated from RT-PCR-positive tissues following chicken embryo inoculation. Sequence analysis of the VP2 gene indicated that all of the isolates from the wild birds encode amino acids A222, I242, I256, I294 and S299 of VP2, which are conserved among strains of very virulent IBDV (vvIBDV). Phylogenetic analysis revealed that the wild bird IBDV isolates are closely related to strains of vvIBDV. An IBDV isolate from a magpie showed 60% mortality in SPF chickens and severe bursal atrophy. The epidemiological implications of IBDV in free-living wild birds are discussed. To our knowledge, this is the first report of vvIBDV in free-living wild birds.