Systematic Veterinary Virology

Avian infectious bronchitis

AVIAN INFECTIOUS BRONCHITIS (IB)

Field diagnosis

• Sudden appearance of respiratory infection with high morbidity and characteristic respiratory symptoms help in field diagnosis. In adult birds, the causes for malformed egg should be analysed in details before confirming it as IB.

Isolation and identification

• Clinical materials
  • Live birds: Tracheal mucus from young chicks
  • Dead birds: Tissue samples from the trachea, kidney, oviduct and caecel tonsils in sterile transport media with antibiotics and dry swabs from the respiratory tract or cloaca
• Isolation systems: Embryonated eggs or tracheal organ culture (TOC). In eggs characteristic lesions include teratological changes in the embryo at the second or third passage consisting of stunted and curled embryos with feather dystrophy and urate deposits in the embryonic mesonephros. The infection in TOCs is characterised by ciliastasis. The lesions have to confirmed by any one of the following antigen identification system. In outbreaks from affected birds, the virus can be isolated using sentinel birds.
• Antigen identification system
  • Fluorescent antibody test (FAT)
  • Immunohistochemistry methods like IPT
  • Antigen competitive ELISA
  • RT-PCR for S gene
  • CDNA probe
• Serotype identification: Since IBV are antigenically distinct identification of correct serotype is essential. Serotype identification is carriedout by
  • Virus neutralization test in eggs, TOCs
  • HI test
  • Monoclonal antibody (serotype) based ELISA
  • Monoclonal antibody (serotype) based immunohistochemistry
  • RT-PCR using serotype specific primers

Serological tests

• The serological tests are normally performed to identify antibodies produced after vaccination. During infection, paired sera sample with a time interval of three weeks will yield clues about infection. Some of the commonly performed serological tests are
  • Virus neutralization test
  • HI test
  • AGID
  • ELISA

Differential diagnosis

• IB should be differentiated from Newcastle disease, Infectious Laryngeal Tracheitis and Infectious Coryza