Evaluation of the immunogenicity, stability, pathogenicity, and immunodepressive potential of four commercial live infectious bursal disease vaccines.

The study was divided into three experiments. In each, day-old specific pathogen free (SPF) White Leghorns were injected subcutaneously with one of the following commercial live infectious bursal disease (IBD) vaccines: Burcell, Bursine, Clone Vac D-78, and S-706. In the first experiment, the immunogenicity of each vaccine was determined by challenge with virulent IBDV at 25 days of age. All four vaccines were equally efficacious in preventing clinical IBDV infection. The second experiment determined the stability and pathogenicity of the four vaccines by successive back passage of each virus in SPF chicks for 4 consecutive weeks. Although all vaccines were capable of spreading to contact controls, only the two intermediate vaccines (D-78 and S-706) produced slightly atrophied bursae and moderate microscopic bursal lesions. However, both vaccines were stable, because neither reverted back to increase virulence nor resulted in morbidity or mortality associated with virulent IBDV after successive passage. In the third experiment, the immunodepressive potential of each vaccine virus was determined by examining the ability of IBD-vaccinated birds to respond to Newcastle disease (ND) virus vaccination. None of the four vaccines was found to be immunodepressive, as all IBD vaccinated birds responded to NDV vaccination.