Immune response and pathogenicity of different strains of infectious bursal disease virus applied as vaccines.

Eight strains of infectious bursal disease virus (IBDV) were characterized by the criteria of immunity and pathogenicity engendered in young chickens. Some strains have been used commercially, and the others are potential candidates for vaccines. They were administered by drinking water, eyedrop, vent drop, and subcutaneous and aerosol routes. The viruses varied widely in pathogenicity in terms of bursal damage, morbidity, and mortality. Immunity induced with different routes of administration also differed markedly when measured by challenge, virus serum-neutralizing antibody titers, and the agargel precipitin test. Maternally derived immunity interfered with stimulation of active immunity by some of the less pathogenic strains. The more virulent strains, however, were able to provide protection under similar circumstances, although bursal damage was frequently severe. Two strains proved relatively virulent by the criteria employed. Characteristics desirable for IBDV strains to be given as vaccines under field conditions to young chickens are discussed briefly.