The History of Infectious Bursal Disease: The Second Period Between 1977 and 2005

Major progress has been achieved since the first historical review of infectious bursal disease (H. N. Lasher and V. S. Davis, Avian Diseases, Vol. 41, pp. 11-19; 1997), much of it between 1977 and 2005. Significant findings in the 1980s were the presence of serotype 2 of infectious bursal disease virus (IBDV) and the diversity of antigenic and immunogenic types of IBDV. In the late 1980s, very virulent IBDV strains emerged and became widespread in many countries by the late 1990s. Soon after the discovery of the antigenic variants, specific commercial vaccines were developed and used successfully in the field. The structure of the virus was discovered, which led to the elucidation of virus genes being responsible for some of the virus' biological functions, including immunogenicity. A consequence of these findings was the development of a new class of recombinant vaccines, which were commercially licensed. Reverse genetics became another tool for virus characterization. The development of monoclonal antibodies allowed the identification of immunoglobulin M positive (IgM+) B cells as the major target cells for infection. A role of macrophages and T cells in IBDV pathogenesis and pathology of the bursa of Fabricius was suggested. New tools for serology and virus identification-ELISA and reverse transcriptase (RT) PCR, respectively-provided new insights in the epidemiology. The widespread use of ELISA kits facilitated the use of vaccines in the face of maternally derived antibodies against IBDV, allowing the determination of time of vaccine breakthrough and therefore vaccine administration.