Molecular Characterization of Newcastle Disease Virus Genotype VII.1.1 from Egyptian Mallard Ducks with Nervous Manifestations

Abstract

In Egypt, Newcastle disease virus (NDV) strains of genotype VII are known to be mild in domestic waterfowl and considered reservoirs. This is the first report for the detection of NDV GVII.1.1 from ducks showing severe clinical signs with high mortalities and nervous manifestations, additionally, isolation of NDV and molecular characterization for full HN and F genes were performed. In the current study, 16 backyard mallard duck flocks showing severe nervous signs with high mortalities were investigated by real-time RT-PCR using primers specific for the Fusion gene of NDV and matrix gene for avian influenza virus (AIV). Fourteen duck flocks tested positive for AIV and only two flocks tested positive for NDV infection. NDV was isolated from the trachea and brain of the same duck from each flock then full HN and F genes were sequenced. The phylogenetic analysis of the F and HN genes indicated that these strains were clustered with NDV genotype VII 1.1. The F gene had a specific mutation that cluster them in a new branch with with A11T in the signal peptide, N30S, T324A, and 480K in the hydrophobic heptad repeat (HRc) compared to the Lasota strain. The duck strains of NDV isolated from the brain had N294K in the hydrophobic heptad repeat-b (HRb) of F protein compared to the strains isolated from the trachea of the same duck, which may have a role in crossing the blood-brain barrier. The HN protein had a specific mutation that clustered them in a new branch with mutations of A4V, R15K in the cytoplasmic region, A28T in the transmembrane domain, and S76L in the HRa. In addition, HN protein had A50T, S54R T232N, P392S, and T443V, and multiple mutations were detected in the neutralizing epitopes specific to strains in the present study (N120G, K284R, S521T) that can alter virus antigenicity. The current study indicated the continuous evolution of NDV strains from genotype VII circulating in Egypt with increasing pathogenicity in ducks. The present findings demonstrated the urgent need for the vaccination of ducks and geese with killed NDV vaccines to reduce economic losses due to virus infection and prevent transmission to chickens helping in ND control in Egypt.