Gumboro is caused by a double stranded RNA virus of the genus Avibirnavirus of the family Birnaviridae.

The disease is present worldwide.

The mortality rate varies with the virulence of the strain involved. Low pathogenicity strains of IBD usually cause low mortality rates; in case of very virulent IBDV, mortality can be up to 100%, resulting in severe economic losses.

The IBD virus is shed by infected chicken in their feces. The virus can persist in the poultry environment (feed, water, litter) for extended periods of time and can be spread by fomites (e.g. equipment, vehicles).

During the acute form, birds in a flock are typically reluctant to move, have ruffled feathers, produce watery diarrhea and may pick at their own vent. They may also be susceptible to opportunist germs that would not usually cause disease. The size, weight and morphology of the bursa changes, depending on the progress of the disease (the bursa of Fabricius is a specialized organ in birds for the formation of cellular blood components).

There is no treatment. Biosecurity and vaccination are the principal methods to control IBD. Both inactivated and attenuated live vaccines are available commercially. Breeder flocks may be immunised to transfer protective antibodies to chickens.

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