Summary
Twenty-four poultry farms in four major provinces of the Lebanon were investigated to verify the first emergence of avian influenza (AI). Both the meat chicken breeders and commercial chicken layers presented a significant average drop in egg production equivalent to 46% and 47.3%, respectively. However, the average drop in egg production in the free-range layers was only 11.1%. Flocks were confirmed as positive for AI by ELISA, clinical signs and pathological lesions. The pathogenicity, including case fatality in affected chickens, was different depending of the types of chicken and farming conditions. The average fatality rates among breeders, commercial layers, free-range layers and broilers were 2%, 2%, 1% and 35%, respectively. The majority of the randomly selected ELISA-positive serum samples collected from different farms showed H9-specific haemagglutination inhibition (HI) antibodies. The direct immunoflorescent antibody test also revealed the presence of H9 antigen in congested brains and in tracheal lesions of broilers. The virus isolated from the brains of broilers was subtype H9N2. Pigs fed with carcasses of affected chickens showed H9-specific HI antibodies at 100%. Farmers (32.3%) serving the affected chickens also revealed these antibodies in their sera.

Keywords
Avian influenza, Chickens, Enzyme-linked immunosorbent assay, H9N2, Haemagglutination inhibition, Humans, Lebanon, Pigs, Viruses.