Evolution of Gumboro; Infectious Bursal Disease Virus

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The infectious bursal disease, avian infectious bursal disease (IBD) or Gumboro disease, is caused by the infectious bursal disease virus (IBDV). The virus infects immature B lymphocytes in the bursa of Fabricius located near the chickens’ cloaca, causing immunosuppression, secondary infections associated with opportunistic pathogens, reduced responses to vaccination programs, and greater clinical reactions to live attenuated vaccines.

In addition to morbidity and mortality, this disease also causes:

• Economic losses associated with secondary infections
• Poor feed efficiency
• Growth delays
• Lack of uniformity
• Delay in reaching market weights.

Control of IBD is primarily done by vaccination

When we think of viruses that can change rapidly and hamper our vaccination efforts, IBDV is rarely one of them. However, this RNA virus has evolved slowly since its discovery in 1962.

This fact became apparent when vaccine failures in broiler flocks revealed the presence of a second antigenic type of IBDV known as a variant. Vaccines against the parent (classic) IBDV did not protect birds against these antigenic variants of the virus.

The terms classic and variant are still used to describe IBDV strains, but we now know that the evolution of the virus has resulted in many new antigenic types. This is a problem, as the commercial vaccines were obtained from IBDV strains that are over 30 years old, and do not resemble the antigenic types of IBDV found in current broiler and layer flocks.

Old vaccines may sometimes provide some level of cross-protection against new IBDV strains, but rarely offer complete protection, and their efficacy is difficult to predict.