B301 - AVIAN INFECTIOUS BRONCHITIS

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B301 - AVIAN INFECTIOUS BRONCHITIS

Nature of the disease
Avian Infectious Bronchitis (IB) is a contagious disease of birds due to a Coronavirus and causing important economic loss in chicken operations.
Classification
OIE, List B disease
Susceptible species
Chicken
Distribution
IB is distributed worldwide, it is present in the Pacific Region where it has been isolated, serologically or clinically, from most PICTs. 
Clinical signs 
The incubation period is short (1-2 days) and signs usually include:
  • In young animals:
    • Gasping, coughing and nasal discharge, 
    • Wet eyes 
    • Swollen sinuses, 
    • Reduction of food consumption and weight gain.
  • In adult: 
    • Gasping and coughing,
    • Drop in production 
    • Production of misshapen soft-shelled eggs with inferior internal quality is often seen and can be permanent.

The mortality may be as high as 25% in young chicks, nephrogenic strains may cause 60% mortality. Adults usually recover after a few weeks.

Post-mortem findings 
  • Accumulation of mucus in the trachea, 
  • Obstruction of nasal passages and sinuses and the air sacs 
  • Tracheal mucous plugs in dead broilers. 
  • Reduction of length and weight of reproductive tract
  • Nephrogenic strains cause pale and swell kidneys, with large amounts of uric acid crystals.
Differential diagnosis 
Specimens required for diagnosis 
IB virus may be isolated from tracheal mucosa during the acute phase of the respiratory form of the disease. Identification of virus can be done by immunofluorescence, electron microscopy, polymerase chain reaction techniques, haemagglutination inhibition tests (HI) or enzyme-linked immunosorbent assays (ELISA).

Serological tests are available and include virus neutralisation, agar gel immunodiffusion, haemagglutination inhibition and ELISA. If the disease exist in the country paired sera should be addressed to the laboratory to demonstrate seroconversion or rise in antibody titre, serology can also be used to monitor vaccination response. 

Transmission   
IB is very contagious and it is shed in respiratory secretion and faeces. It can be transmitted by aerosols, contaminated feed and water, contact with animals or material. Morbidity often reaches 100%.
Risk of introduction   
IB can be introduced through the importation of infected chickens or contaminated husbandry material. 
Control / vaccines  
Killed and attenuated lived vaccines are commercially available, it seems that live vaccines protect against a wider range of strains, although they can cause a mild respiratory infection. 

Once introduced IB is difficult to eradicate and require strict isolation of infected premises and slaughtering of flocks.

References
  • Infectious Bronchitis, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 1979-1980
  • Office International des Epizooties, 2002
  • SAVILLE P. South Pacific Commission, Infectious Bronchitis and Infectious Laryngotracheitis, Animal Health Advisory Leaflet 4, Noumea 1996