Infectious bursal disease (IBD) is caused by the infectious bursal disease virus (IBDV) which mainly infects immature B-lymphocytes in young chickens. It causes an immune suppression that leads to secondary infections in convalescent birds and symptoms to include depression, watery diarrhea, ruffled feathers, and dehydration. Morbidity is high and mortality is usually low, but some very virulent strains are capable of causing 60% or higher mortality. The virus is found worldwide, and diagnosis is through clinical evaluation of the cloacal bursa, ELISA to detect the presence of antibodies to IBDV in convalescent chicks, or molecular identification of the viral genome.