All about Infectious Bursal Disease (Gumboro disease, IBD)

All about Infectious Bursal Disease (Gumboro disease, IBD):
 1. Cause:
The disease is caused by a Birnavirus of serotype 1. Virus strains can be divided in classical and variant strains.The virus is very stable and is difficult to eradicate from an infected farm.
2. Transmission:
IBD virus is very infectious and spreads easily from bird to bird by way of droppings. Infected clothing and equipment are means of transmission between farms.
3. Species affected:
Chickens and turkeys appear to be natural hosts.
4. Clinical signs:
Clinical IBD occurs usually between 3 and 8 weeks of age depending on maternal antibody levels. 
Affected birds are listless and depressed, pale, huddling producing watery white diarrhea. Mortality varies. 
Usually new cases of IBD have a mortality rate of about 5 to10% but can be as high as 60% depending on the pathogenicity of the strain involved. 
Highly pathogenic strains are called “very virulent” IBD (vvIBD)  resulting in high mortality. 
Subclinical IBD occurs with infections before 3 weeks of age. Early IBD infection result in permanent immunosuppression without mortality. 
Immunosuppression is economically important due to increased susceptibility to secondary infections especially in the respiratory tract. Gumboro disease related diseases such as inclusion body hepatitis are also more frequent in these birds.
 In broilers this form of the disease results in bad performance with lower weight gains and higher feed conversion ratios.
5. Diagnosis:
Typical clinical signs and post mortem lesions are found after IBD infection. Post mortem lesions; in acute cases the bursa of Fabricius is enlarged and gelatinous, sometimes even bloody. 
Muscle haemorrhages and pale kidneys can be seen. Infection by variant strains is usually accompanied by a fast bursal atrophy (in 24-48 hours) without the typical signs of Gumboro disease. 
Also in chronic cases the bursa is smaller than normal (atrophy). 
The bursa destruction is apparent on histologic examination. The lack of white blood cells (lymphocytes) results in a reduction in the development of immunity and decreased resistance of the birds to other infections. 
Histopathological examination, serology, virus isolation and PCR are confirming tools. 
IBD can be confused with sulfonamide poisoning,  aflatoxicosis, and pale bird syndrome (Vitamin E deficiency).
6. Treatment:
No treatment is available for IBD.
7. Control:
Vaccination of breeders and young chicks is the best means of control. 
The induction of a high maternal immunity in the progeny of  vaccinated breeders, together with the vaccination of the offspring is the most effective approach to successful IBD control. 
A variety of live and inactivated vaccines have been developed to enhance the control of classical, variant and vvIBD challenges.