Immunization of chickens for the control of infectious bursal disease

Full-length sequence analysis of four IBDV strains with different pathogenicities

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' non-coding region of segment B among IBDV strains. The deduced amino acid sequences of the VP1 protein varies in length among the strains analyzed. The RNA-dependent, RNA-polymerase motifs within VP1 and the VP5 protein were highly conserved among isolates. Although within the VP2 processing site, amino acid sequence of Lukert was similar to the classical while the Edgar CCA, and CEA were more similar to the very virulent strains, it was determined that these strains have sequence characteristics of the classical strains. In addition, close relatedness between Lukert, Edgar CCA and CEA was observed. 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' non-coding regions of segment A revealed that 9109 is more similar to the very virulent strains compared to the classical strains. In the VP2 protein, several amino acids were conserved between variant E and 9109 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 not designate a particular strain as very virulent, classical, or variant.

Characterization of the antigenic, immunogenic, and pathogenic variation of infectious bursal disease virus due to propagation in different host systems (bursa, embryo, and cell culture). I. Antigenicity and immunogenicity

In vitro and in ovo virus neutralization assays were conducted to assess the role of different host systems in infectious bursal disease virus (IBDV) antigenic and immunogenic variation. Four different strains, two variant (1084 E and GLS) and two standard (Edgar and STC), were propagated separately in the bursa of Fabricius and embryos, and were compared with cell culture-adapted preparations of the homologous strains. Chicken polyclonal antisera were prepared against each IBDV and neutralizing antibody titres were determined. Normalized IBDV antibody concentrations were used in neutralization assays against homologous and heterologous IBDVs in 10-day-old specific pathogen free embryos. Both antigenic and immunogenic changes occurred in IBDVs evaluated, as evidenced by differences in the ability of normalized antibody to neutralize IBDV propagated in different host systems. Antibody induced by bursal-derived IBDV neutralized all isolates equally well, whereas antibody induced by cell culture-derived virus neutralized bursal-derived IBDV much less effectively.

A comparison of three different regimens of infectious bursal disease vaccination in chickens

Five days old progeny chicks from breeders which have received primary and booster doses of live infectious bursal disease vaccine, demonstrated precipitating antibodies unlike progenies from single dose vaccinated breeders. All chicks from the two different groups of breeders were however seronegative at 22 days of age, despite vaccination at 7 or 14 days of age. Post vaccination seroconversion was first noticeable at 32 days in the group of chicks vaccinated at 7 days. Post challenge mortalities was significantly lower (P less than 0.05) and organ lesions very significantly minimized (P less than 0.01) in 7 day old vaccinated group than in 14 or 28 days old vaccinated chicks. These results showed that early (7 days) IBD Vaccination was superior to vaccination at 14 or 28 days, in terms of antibody response and protectivity against mortalities and bursal lesions.