Introduction
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.
Signs
- 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.
Diagnosis
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).
Treatment
Sodium salicylate 1gm/litre (acute phase) where permitted – antibiotics to control secondary colibacillosis (q.v.).
Prevention
Live vaccines of appropriate sero-type and attenuation, possible reactions depending on virulence and particle size.