Submitted to: Virus Genes
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/18/2006
Publication Date: 6/1/2007
Citation: Petkov, D., Linnemann, E., Kapczynski, D.R., Sellers, H. 2007. Full-length sequence analysis of four IBDV strains with different pathogenicities. Virus Genes. 34(3):315-326. Interpretive Summary: Infectious bursal disease virus (IBDV) causes an acute, highly contagious, immunosuppressive disease in chickens that results in significant economic losses. Birds infected with IBDV display increased mortality and are predisposed to secondary infections. Isolates of IBDV are generally classified as classical, variant, or very virulent based on severity of disease and genetic analysis. Molecular characterization of the complete genome of four IBDV strains revealed numerous differences between all isolates that would not be evident if individual genes were used for analysis. The results indicate use of the complete genomic sequence information is essential for thorough typing and designation of IBDV isolates as classical, variant, or very virulent.
Technical Abstract: Characterization of field isolate 9109, Lukert, Edgar cell culture-adapted (CCA), and Edgar chicken embryo-adapted (CEA) serotype 1 IBDV strains using full length genomic sequences is reported. IBDV genomic segments A and B were sequenced and the nucleotide and deduced amino acid (aa) sequences were compared with previously reported full-length sequenced IBDV strains. We found that the viral protein VPX and amino acid sequences between aa 202-451 and 210-473 of VP2 but not the entire VP2 protein are the best representatives of the entire IBDV genome. The greatest variability was found in the VP2 and 5’ noncoding region of segment B among IBDV strains. The RNA-dependent, RNA-polymerase motifs within VP1 and the VP5 protein were highly conserved among isolates. Although phylogenetic analysis of the VP1, VP3, and VP4 proteins indicated that 9109 is a classical type virus, this isolate shares unique amino acid changes with very virulent strains within the same proteins. Phylogenetic analysis of the 3’ and 5’ noncoding regions of segment A revealed that 9109 is more similar to the very virulent strains compared to the classical strains. Thus it appears that 9109 isolate has characteristics of classical, very virulent, and variant strains. Our analysis indicates that although VPX amino acid comparison may be initially useful for molecular typing, full-length genomic sequence analysis is essential for thorough molecular characterization as partial sequences may designate a particular strain as very virulent, classical, or variant.