Characterization of avian influenza H9N2 and Newcastle disease virus isolated from vaccinated chickens in upper Egypt

Abstract EN

In this study, 50 vaccinated broiler flocks and one layer flock from Beni Suef, Fayoum and Minia Governorates were investigated.

Necropsy lesions were suggestive of LPAI-H9N2 or NDV.

Samples including tracheal swabs and organs were subjected for viral isolation and molecular characterization.

Specific RT-PCR for the F-gene of NDV and the HA gene of the LPAI-H9N2 viruses was used.

Virus isolation and primary identification using HI test revealed 37.5 and 43.3-46.2% prevalence for LPAI-H9N2 and NDV viruses, respectively.

Phylogenetic analysis of partial sequences of the F gene showed that NDV viruses belong to genotype II and VII-1.1.

as indicated by the F0 protein proteolytic cleavage site motifs (aa112-117) of the NDV strains F-gene.

The vNDV isolates were 98.7-99.3% and 96.6-98.9% identical to each other based on nucleotide and amino acid identities, respectively.

Compared to their counterpart isolates; the lentogenic strains shared 98-99.2% and 96.3-98.1% nucleotide and amino acid identities to the LaSota reference strain.

The LPAI-H9N2 phylogeny of the HA gene showed that the 2 isolates obtained in this study are related to each other and related to recent 2016-2018 Egyptian H9N2 strains.

Notably, the 2 strains showed higher identity (≥99%) to recent Israeli 2018 isolates with several amino acid changes.

The current study revealed widespread of both NDV and LPAI-H9N2 viruses.

The vaccine failure and the mismatch between the vaccine and circulating NDV viruses is the most probable cause of current outbreaks.

LPAI-H9N2 viruses are divergent from their ancestral viruses in Egypt indicating continuous circulation and vaccine pressure-induced mutations.