Abstract
A total of 50 poultry farms of commercial broilers (N = 39) and commercial layers (N = 11) suffered from respiratory problems and mortality during the period from January 2016 to December 2017 were investigated. Also, samples were collected from quail (N = 4), Bluebird (Sialis, N = 1), and Greenfinch (Chloris chloris, N = 1) for analysis. Respiratory viral pathogens were screened by PCR and positive samples were subjected to virus isolation and genetic identification. Antigenic relatedness of isolated avian influenza (AI) H5 subtype was evaluated using cross-hemagglutination inhibition. Results revealed that the incidence of single virus infections in commercial broilers was 64.1% (25/39), with the highest incidence for ND (33.3%) and H9N2 (20.5%), followed by H5N1 (7.7%) and H5N8 (2.7). Meanwhile, H9N2/ND mixed infection was the most observed case (7.7%). Other mixed infections H5N1/ND, H5N1/H9N2/ND, H5N1/H9N2/ND/IB, H9N2/IB, and H9N2/ILT were also observed (2.6% each). In commercial layers, H5N1 and ILT were the only detected single infections (18.1% each). Mixed H9N2/ND was the most predominant infection in layers (27.3%). Other mixed infections of H9N2/IB, H5N1/H5N8/H9N2, and H9N2/ND/IB were observed in 3 separate farms (9.1% each). The H5N8 virus was detected in one quail farm and 2 out of 3 wild bird's samples. Partial HA gene sequence analysis showed the clustering of the selected AI H5N8 within the 2.3.4.4 clade, while H5N1 clustered with the clade 2.2.1.2. Interestingly, the H5N8 isolated from chickens possessed 6 amino acids substitutions at HA1 compared to those isolated from wild birds with low antigenic relatedness to AI H5N1 clades 2.2.1 or 2.2.1.2. In conclusion, mixed viral infections were observed in both broiler and layer chickens in Egypt. The detected triple H5N1, H9N2, and H5N8 influenza co-infection raises the concern of potential AI epidemic strain emergence. The low genetic and antigenic relatedness between AI H5N1 and H5N8 viruses suggest the need for modification of vaccination strategies of avian influenza in Egypt along with strict biosecurity measures.