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Infectious Bronchitis, IB - 793b Variant Sudden Death Syndrome in Broiler Parents

Extracted From:
A Pocket Guide to
Poultry Health
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By Paul McMullin
© 2004
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A Coronavirus infection of chickens with a morbidity of 50-100% and a mortality 0-25%, depending on secondary infections. Infection is via the conjunctiva or upper respiratory tract with an incubation period of 18-36 hours. The infection spreads rapidly by contact, fomites or aerosol. Some birds/viral strains can be carriers for up to 1 year.

The virus, which may survive 4 weeks in premises, is sensitive to solvents, heat (56°C for 15 mins), alkalis, disinfectants (Formal 1% for 3 mins).

Poor ventilation and high density are predisposing factors.


  • Sudden death.
  • Muscular shivering.
  • Otherwise as for standard IB.

Post-mortem lesions

  • Oedema of pectoral muscles and subcutaneously on abdomen, lesions progress to necrosis and scarring of deep pectorals in convalescence.
  • In layers the ovules may be intensely congested.
  • Other lesions of 'classical' IB may be encountered.


3-5 passages in CE allantoic cavity, HA-, typical lesions, FA, ciliostatic in tracheal organ culture, cell culture (Vero, CK) only after adaptation Serology: HI, Elisa (both group specific), SN (type specific), DID (poor sensitivity, short duration, group specific).


Sodium salicylate 1gm/litre (acute phase) where permitted - antibiotics to control secondary colibacillosis (q.v.).


Live vaccines of appropriate sero-type and attenuation, possible reactions depending on virulence and particle size.

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