B309 - INFECTIOUS BURSAL DISEASE

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B309 - INFECTIOUS BURSAL DISEASE

Nature of the disease
Infectious bursal disease (IBD, Gumboro disease) is an immuno-suppressive disease of domestic poultry caused by a birnavirus. There are three types of IBD, the highly virulent (vv IBD), the US IBD and the subclinical IBD.
Classification
OIE List B disease
Susceptible species
The domestic fowl is the natural host. Sub-clinical infection may occur in turkeys.
Distribution
Hyper-virulent strains of IBD have been reported in Europe, America, South East Asia and Japan. Although low pathogenicity strains of IBD occur in the Pacific (confirmed or suspected in most countries), there is no evidence of the presence of hyper-virulent strains to date.
Clinical signs 
Disease is most common in 3 to 6 weeks old birds, however severe infection occurs in Leghorn up to 18 weeks. One of the earliest signs is for birds to pick at their own vent. Other signs include:
  • Infection by opportunist germ which are not normally pathogenic
  • Poor body weights and feed conversions
  • Reluctance to move
  • Depression
  • Anorexia
  • Ruffled feathers
  • Trembling
  • Watery diarrhoea
  • Sudden death

 Morbidity rates are high resulting in severe economic losses. Mortality rates of up to 25% in broilers and 60% in layers may occur.

Post-mortem findings 
  • Cloacal bursa is enlarged, swollen and haemorrhagic in birds dead of the disease and is atrophied in recovered birds
  • Dehydrated carcass
  • Skeletal muscles dark with haemorrhages (especially thigh and pectoral muscles)
  • Thymus opaque with thickened gelatinous capsule 
  • Bone marrow fatty and yellow or pink
  • Liver may be swollen
  • Kidneys swollen and fatty 
  • Increased mucus in the intestines
Differential diagnosis 
Other diseases that need to be differentiated from hyper-virulent IBD on clinical or pathological grounds include: 
  • Marek's disease
  • Mycotoxicosis
  • Coccidiosis
  • Haemorrhagic syndrome
  • Avian adenovirus infection
  • Infectious bronchitis
Specimens required for diagnosis 
Samples should be collected from sick or freshly dead birds. Fresh bursa and spleen for virus isolation. Samples of bursa, spleen, intestines, caecal tonsil, liver and kidney should be collected in neutral buffered formalin for histopathology Blood samples for serology.
Transmission   
Chickens infected with the IBD virus shed the virus in their feces. Feed, water, and poultry house litter become contaminated. Other chickens in the house become infected by ingesting the virus. The lesser mealworm (Alphitobus diaperinus) has been shown to carry the virus. Because of the resistant nature of the IBD virus, it is easily transmitted mechanically among the farms by people, equipment and vehicles.
Risk of introduction   
The disease could be introduced with infected poultry, material or manure from infected country.
Control / vaccines  
There is no treatment. 

Recovered and vaccinated birds can carry and shed virus for long periods. Control of the disease implies depopulation and rigorous disinfection of contaminated premises. Because of the stability of the virus and its ability to spread readily with infected birds and contaminated fomites, strict quarantine measures and movement restrictions should be used. 

Immunisation is the principal method to control IBD. Immunisation of breeder flocks is especially important, to confer maternal antibodies that will protect chickens from early infection. Both inactivated and attenuated live vaccines are available. In many areas inactivated vaccines have given excellent control of IBD, but in some areas where variant virus strains have emerged, there have been vaccine breakdowns. As a result, variant strains have been incorporated into vaccines and inactivated vaccines using attenuated virus strains have been developed.

References
  • BUTCHER GD and MILES RD, Infectious Bursal Disease (Gumboro) in Commercial Broilers, University of Floridia
  • GEERING WA, FORMAN AJ, NUNN MJ, Exotic Diseases of Animals, Aust Gov Publishing Service, Canberra, 1995, p.135-139
  • IBD, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 1924-1925,
  • Office internationale des epizooties, 2002