Molecular Characterization of Avian Influenza H9N2 Viruses Detected in Broiler Chickens in the Middle Region of Saudi Arabia

Sabry, Ahmed; Ibrahim, Mahmoud; Alkhalaf, Abdullah; AboElkhair, Mohammed

doi:10.21608/jcvr.2025.462644

Molecular Characterization of Avian Influenza H9N2 Viruses Detected in Broiler Chickens in the Middle Region of Saudi Arabia

Document Type : Original Article

Authors

10.21608/jcvr.2025.462644

Abstract

Background: Since its first introduction in 1998 to Saudi Arabia (SA), Low pathogenic avian influenza virus (LPAIV) H9N2 has a widespread in poultry flocks in all regions inducing serious economic losses.
Methods: Thirteen broilers’ farms from the middle region in SA of ages ranged between 11:23 days-old, suffering from respiratory distress, with variable mortality percentage were investigated. All tested flocks were vaccinated for (AIV) H9N2, Newcastle disease virus (NDV), and Infectious bronchitis virus (IBV). All flocks were screened for the presence of AIV (H9, H5 and H7) subtypes, NDV and IBV using real time RT-PCR (rRT-PCR) followed by complete hemagglutinin (HA) and neuraminidase (NA) sequencing by next generation sequencing (NGS) for one selected sample.
Results: Eleven out of the thirteen tested flocks were positive for AIV H9N2 and NDV detection, while all the flocks were negative for H5 and H7 AIVs. Only four flocks were positive for IBV. Sequence analysis of the HA gene revealed cleavage site motif sequences similar to low pathogenic AIV. The aa identity percentage of HA gene was high between the current study strain in 2022 and the SA H9N2 2020 strain (99.4%), however it was about 92%, and 91% with the SA strains in 1998 and 2002 respectively. The aa identity percentage of NA gene was about 90% and 87% when compared with the early SA H9N2 strains in 1998 and 2006 respectively with altered glycosylation patterns. The NA protein harbors five amino acids substitutions in the hemadsorping (HB) and frame active sites (K368T, S370L, D401N, R403W and Q432R). These 5 substitutions were not detected in older published data from SA till 2006.
Conclusions: The current study highlights the severe endemic situation of H9N2 virus in poultry flocks in SA with continuous evolution. Multiple aa mutations reported in recently circulating SA H9N2 viruses might alter virus antigenicity, increase the virus virulence and increase receptor affinity toward human receptor with increased human infection possibility.

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