Gumboro Disease or Infectious bursal disease virus (IBDV) is a disease of chickens targeting the cloacal bursa, which is a primary lymphoid organ located dorsally to the cloaca and is responsible for the development and maturation of B cells in young poultry. Atrophy of the bursa, which includes the loss of B lymphocytes, occurs ~7–10 days after IBDV infection. Virulent strains of IBDV can result in mortality of up to 60%. Control is best achieved by improved biosecurity and vaccination, since no treatment is currently available. The virus infects chickens via oral ingestion or inhalation. The virus is shed in the feces and transferred from house to house by fomites. Chickens are most susceptible to clinical disease at 3–6 weeks.