Occurrence: Worldwide.
Species affected: All.
Age affected: All.
Causes: Type A Orthomyxoviruses.
Effects: Reportable disease. Respiratory distress, coughing, sneezing, rales, depression, sinusitis, emaciation, feed refusal, nervous signs and diarrhoea. In layers, there is a drop in egg production and shell quality. Mortality is rapid with virulent strains.