Pathogenicity and immunosuppressive properties of infectious bursal disease "intermediate" strains.

This study was conducted to test the pathogenicity and immunosuppressive effects of seven commercially available infectious bursal disease (IBD) vaccines. These vaccine strains are intermediate in their pathogenicity in susceptible specific-pathogen-free (SPF) chickens. One-day-old and 3-week-old SPF chickens were vaccinated with these vaccines. Two weeks after IBD vaccination, they were vaccinated with Newcastle disease virus (NDV). The pathogenic and immunosuppressive effects of the IBD vaccines were evaluated by the antibody response to NDV vaccination, the bursa: body weight index, and histopathological lesions of the bursa. It was found that these strains were highly variable in their virulence and immunosuppressive properties. Three of the strains tested were found to be highly virulent and immunosuppressive; two others were moderate; and two could be classified as mild.