Gumboro

Gumboro Disease or Infectious Bursal Disease (IBD) is one of the most common diseases of commercial poultry in Asia. In the clinical acute form (vvIBDV), the disease causes significant economic losses due to mortality, reduced performance and immunosupression that lead to increased susceptibility to other diseases. The IBD virus is extremely resistant to environmental conditions and chemicals. Therefore the control of the disease must take into consideration strict biosecurity combined with an effective vaccination program. The following articles review the available knowledge about the disease, the virus, the clinical signs and the role of different elements of the immune system. At the conclusion of these articles, a prevention program is offered, which includes elements of biosecurity and a comprehensive list of vaccination programs for breeders, broilers and commercial layers that in my experience have worked effectively in Asian countries.

What is Gumboro disease?

What causes infectious bursal disease (more commonly known as Gumboro Disease)?
Gumboro disease is caused by the infectious bursal disease virus (IBDV). This is a small, hardy Avibirnavirus belonging to the family Birnaviridae. There are two serotypes. Serotype 1 is a pathogenic type isolated from chickens. Serotype 2 is apathogenic (does not cause any clinical disease) and was originally isolated from turkeys. Both serotypes can be differentiated by cross-neutralisation assays. The organism is resistant to a great range of temperatures, disinfectants and pH. It is therefore very stable during environmental exposure and can survive for up to four months. Certain disinfectants like formaldehyde, glutaraldehyde, chlorine and iodophore based products are however able to destroy it.

How does the virus cause disease in chickens?
The main target cells for IBD Virus replication are the immature B lymphocytes in the Bursa of Fabricius (BF). The BF is the organ responsible for disease protection in young birds, as it is where B lymphocytes (cells of the humoral immune system) are programmed to produce specific antibodies in response to disease and also to vaccine agents in birds. If the IBD virus damages the BF in young chickens, it will destroy the immature B lymphocytes, causing lymphoid depletion of the bursa. The BF will then not be capable of programming sufficient numbers of lymphocytes and the chicken becomes immunosuppressed (not capable of protecting itself against any disease agent).

The severity of the disease is directly related to the number of susceptible B cells present in the Bursa at the time of infection. The time when chickens are most susceptible is therefore between 3 and 6 weeks, when the Bursa of Fabricius is at its maximum rate of development and the follicles are filled with immature B lymphocytes. Virus replication also occurs in other lymphoid organs like the spleen and cecal tonsils but to a lesser extent.

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