Monitoring field strains key to successful vaccination against IBDV

Infectious bursal disease virus (IBDV) is a serious disease in broiler flocks. Maternal immunity can be achieved through vaccinating the breeder flock. However, that’s no guarantee for complete immunity of the offspring. Usually also proper vaccination of the broiler flock is needed. In order to let this be successful, monitoring field strains is essential.  
 
By Daral J. Jackwood, PhD
Professor
The Ohio State University, Columbus, OH USA
 
More than 60 years of research and experience have made it clear that infectious bursal disease in broilers is here to stay, and that unless it’s managed, considerable losses can occur.
Vaccines are the best tool we have to combat infectious bursal disease virus (IBDV), but too often success is only marginal unless we understand the evolving nature of this pathogen, monitor carefully for changes and adjust the vaccine protocol accordingly.
The strains of IBDV circulating in commercial broiler flocks today are very different from the ones that were identified 6 decades ago. It wasn’t until the 1980s we realized there was more than one type of IBDV.
IBDV’s changing nature
The most common reason for changes in the strains of IBDV is antigenic drift, which is due to random, minor genetic mutations. The changing nature of IBDV is due in part to its genome. It’s a double-stranded RNA virus, which is more likely than a virus with a DNA genome to have genetic mutations.
These mutations enable more recently evolved IBDVs to outcompete older or ancestral IBDV strains. They may evade the neutralizing antibodies produced after IBDV vaccination, or they may replicate faster or be transmitted more easily.
The rate that IBDV changes its antigenic structure is slow compared to some other RNA viruses, such as infectious bronchitis virus (IBV), but given enough time and selection pressure, IBDV will mutate and circumvent our vaccination efforts unless we make necessary adjustments.
Potential for permanent damage
IBDV is an immunosuppressive pathogen. It’s especially damaging if chicks are infected during the first 3 weeks of life. That’s because IBDV infects immature B cells in the bursa of Fabricius. If these B cells in young birds are eliminated by infection, not enough will go on to mature into antibody-producing plasma cells. The result is permanent damage to the bird’s immune system, which sets the stage for costly secondary infections. That’s why it’s critically important to protect young broilers from infection.
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