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Introduction

A Coronavirus infection of chickens, with much antigenic variation. The condition has a morbidity of 10-100% and mortality of 0-1%. Infection is via the conjunctiva or upper respiratory tract. There is rapid spread by contact, fomites or aerosol. A few birds are carriers up to 49 days post infection.

The virus is moderately resistant and may survive 4 weeks in premises. Poor ventilation and high density are predisposing factors.

Signs

• Drop in egg production (20-50%).

• Soft-shelled eggs.

• Rough shells.

• Loss of internal egg quality.

• Coughing, sneezing.

• Rales may or may not be present.

Post-mortem lesions

• Follicles flaccid.

• Yolk in peritoneal cavity (non-specific.

Diagnosis.

3-5 passages in CE, HA-, typical lesions, FA. Serology: HI, SN, Elisa, DID. Differentiate from Egg Drop Syndrome, EDS­76

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, although reactions can occur depending on prior immunity, virulence, particle size (if sprayed) and general health status. Maternal immunity provides protection for 2-3 weeks. Humoral immunity appears 10-14 days post vaccination. Local immunity is the first line of defence. Cell-mediated immunity may also be important.