Highly pathogenic avian influenza A virus (H5N1) has diverged antigenically and genetically since its initial detection in Asia in 1997. Viruses belonging to clade 2.2 in particular have been reported in numerous countries with the majority occurring in Egypt. Previous reports identified antigenic similarities between viruses belonging to clade 2.2. However, poultry and human viruses isolated in northern Egypt during 2007 and 2008 were found to be antigenically distinct from other clade 2.2 viruses from this country. Genetic analysis of the hemagglutinin revealed a high degree of nucleotide and amino acid divergence. The antigenic changes in Egyptian viruses isolated during 2007-08 necessitated that two of these strains be considered as potential H5N1 pre-pandemic vaccine candidates.

Domestic ducks have been implicated in the dissemination and evolution of H5N1 highly pathogenic avian influenza (HPAI) viruses. In this study, two H5N1 HPAI viruses belonging to clade 2.2.1 isolated in Egypt in 2007 and 2008 were analyzed for their pathogenicity in domestic Pekin ducks. Both viruses produced clinical signs and mortality, but the 2008 virus was more virulent, inducing early onset of neurological signs and killing all ducks with a mean death time (MDT) of 4.1 days. The 2007 virus killed 3/8 ducks with a MDT of 7 days. Full-genome sequencing and phylogenetic analysis were used to examine differences in the virus genes that might explain the differences observed in pathogenicity. The genomes differed in 49 amino acids, with most of the differences found in the hemagglutinin protein. This increase in pathogenicity in ducks observed with certain H5N1 HPAI viruses has implications for the control of the disease, since vaccinated ducks infected with highly virulent strains shed viruses for longer periods of time, perpetuating the virus in the environment and increasing the possibility of transmission to susceptible birds.

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In the present study, 3 pooled proventricular homogenates were collected from 3 broiler flocks, of chicken 15 to 30 days old, from Monofia Governorate. The 3 flocks were suffered from low growth rate, poor feed conversion rate, uneven growth and increased mortalities. Necropsy of dead chickens revealed proventriculitis with increased proventriculus size. IBD viral antigen was detected in the pooled proventricular homogenate of each flock by AGPT using reference antibodies against IBDV and RT-PCR technique. No other viruses were detected; such as Reo virus, CAV, NDV, IBV and ALV-J. Further characterization of the IBDV isolates were conducted by RFLP assay on PCR products using MboI and BstOI restriction enzymes. Results demonstrate that the 3 IBDV isolates are identical in their RFLP pattern and related to the Del/E variant strain of IBDV.