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Infectious Bronchitis

Infectious Bronchitis in chickens

Infectious Bronchitis (IB) is a viral disease affecting chickens of all ages.

Disease overview

Infectious Bronchitis is found worldwide. Infectious Bronchitis virus (IBV) targets not only the respiratory tract but also the uro-genital tract. IBV mainly causes respiratory disease in the infected birds and also drops in egg production in layers and breeders. Kidney damage can also occur.

The economic impact of Infectious bronchitis is mainly due to:

  • Poor growth performance and mortality due to the respiratory disease in broilers
  • Egg production losses in layers and breeders
  • Losses caused by renal damage may be seen in broilers, layers and breeders

The negative effects of an IB infection can be prevented by vaccination and implementing sound biosecurity principles.

Clinical signs of Infectious Bronchitis Virus (IBV) infection

IBV affects the respiratory and urogenital tract in infected birds.

Clinical signs

Birds of all ages are susceptible to infection but the clinical signs may vary. The first recognized and most conspicuous signs are the respiratory signs, hence the name Infectious Bronchitis. However, the pathogenicity of the virus for the oviduct in very young chicks or birds in production is often more important. The kidneys may also be affected.

The following may be seen:

  • Young chickens are depressed and huddle under the heat source.
  • Respiratory signs – gasping, coughing, tracheal rales and nasal discharge.
  • Birds in lay have a marked drop in egg production and an increased number of poor quality eggs may be produced.
  • The external and internal quality of the eggs may be affected, resulting in misshapen or soft-shelled eggs with watery content.
  • The hatchability rate of the eggs may be affected.
  • When the kidneys are affected, increased water intake, depression, scouring and wet litter are commonly observed.

In the graphs below it can be seen how an IB infection of layers and breeders causes egg production losses and poor quality eggs in unprotected birds.

Diagnosis of Infectious Bronchitis (IB)

Isolation or identification of the causative agent is required for a definitive diagnosis of IB.

Clinical signs

Diagnosis of Infectious Bronchitis on the basis of clinical signs alone is very difficult.

  • Respiratory signs – Respiratory signs similar to IB are observed in many other respiratory diseases such as Newcastle Disease, Infectious Laryngotracheitis or Pneumovirus infections. Often these diseases may present themselves in milder forms making it impossible to distinguish one from the other.
  • Decreased egg production and poor egg quality – The sign “egg drop” is even less specific. Post mortem findings are often not conclusive.

Laboratory tests

Laboratory tests to identify the viral genome, viral antigen (proteins) or antibodies against the virus are important to confirm IBV infections.

Testing serum samples at intervals (for example at the time of the clinical signs and 2 or 3 weeks later) provide the best basis for serological diagnosis. This is also applicable for monitoring vaccination results.

Vaccination against Infectious Bronchitis (IB)

Vaccination is the backbone of Infectious Bronchitis (IB) control. Two types of vaccine are used:

  • Live vaccines (attenuated viruses)
  • Inactivated vaccines (killed viruses), usually formulated in an oil emulsion adjuvant

Massachusetts serotype of IBV

The Massachusetts serotype was originally described in 1941, and is considered the classical IBV type. Vaccines based on this serotype provide a fairly broad spectrum of protection against other serotypes.

Vaccine developments

New developments in the field of IB vaccines include spike swapping. The concept consists of swapping part of the spike (S) protein of one IB virus with that of another serotype. Vaccination results in immunization against both types of viruses. This technology may give hope for improved IB control in the future.

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