About Infectious Bursal Disease (IBD)

One of the most common viral infections in chickens, infectious bursal disease (IBD) can cause not only a variety of debilitating clinical signs, but also an underlying immunosuppression that leads to poor growth and performance, with significant economic impact on the poultry industry. It cannot be treated, but vaccination can aid in the prevention of disease caused by the virus.

Cause, Transmission, & Evolution

Infectious bursal disease (IBD) is a disease of chickens caused by a virus that destroys lymphocytes in the bursa of Fabricius, a specialized organ of a bird’s immune system. The virus is highly contagious to other chickens via their feces, and once established can be very difficult to eradicate, especially in farm and production settings.

IBD is also called Gumboro disease, after the town of Gumboro, Delaware, U.S., where it was discovered in 1962. It is widely found in chickens all over the world. Vaccination has helped control the disease for many years, but new IBD strains are frequently emerging. In the late 1980s a very virulent strain emerged in vaccinated flocks in Europe and spread rapidly across the globe, while in North America a more sub-clinical variant form arose.

Strains, Symptoms, & Disease Impact

IBD mainly affects younger chickens up to 6 weeks old, whose bursas are still under development. The clinical and sub-clinical manifestations vary depending largely on virus strain; these can be grouped into three categories:

 

 

 STRAIN TYPE     

                                 

                        IMPACT

  Classic                  

 

  • Bursal inflammation / lesions
  • Listlessness and wasting
  • Muscle hemorrhaging
  • Moderate mortality rates
  • Immunosuppression

  Variant

   

  Primarily sub-clinical, with few external signs but inwardly showing bursal atrophy                 

  and underlying  immunosuppression

  Very virulent

 

   Severe clinical signs including:

  • Bursal and muscle hemorrhaging
  • Listlessness, wasting, and poor overall appearance
  • Extreme bursal atrophy
  • High mortality rates
  • Severe immunosuppression (in birds that do survive)

 

Even in the absence of external clinical signs, the immunosuppressive effects of IBD can cause poor growth and performance, leading to major economic loss:

  • Reduced broiler carcass quality and lack of uniformity increases production costs
  • Egg production is reduced in layers, whose genetics have been found to be particularly susceptible to the disease
  • Birds are more prone to secondary infections and less responsive to other vaccines, leading to increased medication costs

Protection And Control

Fortunately, while IBD cannot be treated, vaccination can aid in its prevention and control, especially in combination with good hygiene practices.

Newly hatched chicks absorb maternal antibodies that protect them from IBD in the early weeks of life before declining as vaccine-induced immunity develops. While still present, maternal antibodies can interfere with some forms of vaccination, leaving the bird with an unprotected window of time often referred to as the "immunity gap." As a result, calculating appropriate timing of vaccine doses can be challenging and laborious, especially because of high variation in levels of maternal antibodies across individual birds. In recent years, vector vaccines have been developed using components that, as shown in published research, experience minimal interference from maternal antibodies,12 allowing for early immunization against IBD with simpler vaccination protocols.

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