Infectious Bursal Disease (IBD) is a highly contagious viral disease that infects the bursa of growing chickens, causing sudden onset and extensive damage to the bursa. The virus belongs to the Birnaviridae family and has two serotypes. The disease spreads orally or through the respiratory route, infecting lymphocytes and macrophages that carry the virus to the bursa. This results in viremia, pyrexia, and complete or partial destruction of the bursa. Surviving birds either quickly regenerate or remain immunosuppressed. Clinical signs include lethargy, poor appetite, and diarrhea. Prevention focuses on vaccination of breeder flocks and control of outbreak

1. Infectious Bursal Disease (IBD)
IBD is a highly contagious and infectious viral disease of the growing chickens characterized by sudden
onset, short course and extensive damage in the bursa of Fabricius followed by death or rapid recovery
and followed by immunosuppression.
Virus
It is also known as Gumboro Disease because of its first recognition in that area. Before 1987, the strains
were not causing so much mortality. After 1987 the strains emerged that cause high mortality. The virus
belongs to the family Birnaviridae and is naked, double stranded and about 55-65 nm in diameter. The
virus has 5 proteins from VP1-VP-5 and has two serotypes Serotype 1 and Serotype 2 which is most
prevalent in turkeys and not reported.
Pathogenesis
The incubation period is about 2-4 days and the infection starts from orally through conjunctiva or
respiratory route, the lymphoid and macrophages are infected and bring the virus to the bursa and
other sites. Viremia and Pyrexia occurs, whereas sudden rise in temperature followed by subnormal
temperature. The bursa is primary site for viral replication. In acute cases complete destruction of bursa
but some regeneration elsewise. T cells remain normal, peripheral B cells highly decreased and
Heterophils enter the necrosed area of Bursa. Ultimately the mortality occurs or the survived birds
quickly regenerate. The sequential changes in cloacal bursa are as:
• Day 3: oedema, hyperemia, high size and may be yellow exudate
• Day 4: size starts to recede after it gains size 2-3 times of its previous size
• Day 5: size is normal but keeps on decreasing
• Day 8: Size is 1/3rd of normal and grey due to necrosis
Post-mortem Lesions
Usually, these lesions are related to bursa and muscles (especially thigh, having hemorrhages), the
complication may be air sacculitis with E. coli and Thymus damage in case of highly pathogenic strain.
However sometimes spleen may be affected showing grey foci dispersed uniformly. Mucosal
hemorrhages may be shown and liver may be friable and swollen and peripherally necrosed. Kidneys
also can have urates and swelling. Overall carcass is dehydrated and bursal condition is related to day of
disease.
Clinical Signs
The subclinical form may remain and reduces the size of bursa from its normal 0.3% of body weight to
less than 0.1 %. However, the damage to the bursa causes immunosuppression. The clinical form shows
overnight sickness. The birds are less active, if moved abnormal gait and low appetite and pick at their
own cloaca. The morbidity is about 20-30%. In advanced stages, birds have watery, mucoid, whitish
diarrhoea and the bursal size is varied. The mortality is about 20% but some severe strains can cause
50% mortality. The mortality follows a bell curve and the survived birds recover rapidly.
Transmission, factors and susceptibility
Light breeds are more susceptible, similarly males have high chances. The chicks which have not
developed bursa and those mature chickens who have regressed their bursa are not susceptible.

2. Transmission doesn’t occur vertically and through air but fomites can cause flock to flock and faeces can
cause within flock transmission. It can tolerate 60 degrees of temperature and organic solvents
however, formaldehyde, chlorine iodophore based products can kill it.
Diagnosis
Diagnosis is based on history, age of flock as well as mortality pattern. However, serological tests VNT,
ELISA, Agar gel diffusion test and antibody testing is available and also inoculation in SPF chicken egg
and watching for mortality is also an option. Differentiate it from Nd and IB on basis that IBD has no
respiratory signs, from Sulphonamide toxicity and Vitamin K deficiency as they have no fever. Liver
lesions match mycotoxicosis so watch for other symptoms
Prevention and control
For immunization live attenuated vaccine is available as well as maternally derived antibodies and virus
antibody complex or virus neutralizing Factor. Preferred is to get chicks from vaccinated breeder flock, in
case of outbreak watch for bursal disease, vaccinate the unvaccinated birds and offer low protein, low
energy diets and keep on giving electrolytes. It has no Public Health importance.