Effect of cocirculation of highly pathogenic avian influenza H5N1 subtype with low pathogenic H9N2 subtype on the spread of infections.

Widespread prevalence of avian influenza H9N2 subtype in the Middle East region and its detection in Egypt in quail in early summer 2011 added another risk factor to the Egyptian poultry industry in addition to highly pathogenic H5N1 subtype. This situation increases the need for further surveillance and investigation of H9N2 viruses in commercial and household chickens. This work describes detection and genetic characterization of recently isolated H9N2 viruses from chicken flocks. Parallel detection and genetic characterization of H5N1 viruses from infections in poultry has also been done to compare the prevalence of the two subtypes in close geographic locations in Egypt. Phylogenetic analysis of the HA gene showed that the Egyptian isolates of H9N2 were grouped together within the quail/Hong Kong/G1/97-like lineage, similar to the circulating viruses in the Middle East, with very close phylogeny to the Israeli viruses. The prevalence of H5N1 viruses from cases recorded in poultry in the nearby areas revealed a marked decrease in disease incidence in commercial broilers but an increased incidence in household birds. The genetic characterization of the H5N1 viruses indicated predominance of the classic 2.2.1 subclade, with evolution of new viruses and no detection for the variant 2.2.1.1 subclade. The cocirculation of the two subtypes, H5N1 and H9N2, of avian influenza may affect the limit of spread and the epizootiologic pattern of the infections for both subtypes, especially when different vaccination and biosecurity approaches are applied in the field level.