Overview of Methods Used in the Diagnosis of Infectious Bursal Disease

Abstract

Infectious bursal disease (IBD) is an infectious viral disease of poultry. It is caused by infectious bursal disease virus (IBDV) that
is a member of the genus Avibirnavirus of the family Birnaviridae. The virion is non-enveloped and consists of a bi-segmented
RNA molecule. The disease occurs in a clinical and subclinical form depending on age at infection. Only young chickens are clinically affected. Severe acute disease of 3-6 week old birds is associated with high mortality but a less acute or subclinical disease
is common in 0-3-week-old birds. This can cause secondary problems due to the effect of the virus on the bursa of Fabricius.
There are two serotypes of IBDV; These are serotype 1 which is pathogenic to chickens and commonly leads to the development
of the clinical form of the disease and serotype 2 is avirulent to chickens. Clinical IBD can be diagnosed by the combinations of
a characteristic sign and post-mortem lesions. Gross lesions are characterized by marked haemorrhages in the pectoral and thigh
muscles. At post-mortem examination bursa of Fabricius, thymus, spleen and kidneys are initially enlarged, however, bursa of Fabricius and thymus are later become atrophic. Histologic lesions showed marked edema, infiltration of heterophiles, hyperaemia
and lymphoid depletion and hyper plastic corticomedullary layer in the bursa of Fabricius. Serological diagnosis of IBD by agar
gel immunodiffusion (AGID), enzyme linked immunosorbent assay (ELISA), virus neutralization test (VNT) and agar gel precipitin test (AGPT) are also possible. Subclinical IBD can be confirmed in the laboratory by detecting viral antigens in tissues. In the
absence of such tests, histological examination of the bursa may be helpful.