Abstract
Background:
Newcastle Disease Virus (NDV) is a major viral disease of poultry that causes outbreaks in chickens in Egypt.

Aim:
The aim of this study was to determine the prevalence and molecular characteristics of NDV and its cocirculation with avian influenza virus in Egyptian domestic poultry.

Methods:
Samples collected from January 2019 to February 2021 from different flock types of vaccinated and nonvaccinated domestic birds in seven governorates in Egypt were tested for NDV. A total of 6268 swab samples from healthy, sick, and recently dead domestic poultry that showed typical clinical signs of NDV or AIV were collected. NDV was successfully isolated from swabs via inoculation of specific pathogen-free embryonated chicken eggs. Hemagglutination Assay (HA) was performed followed by RT-PCR of positive HA samples. Genotyping of these isolates was performed by sequencing the full fusion (F) gene.

Results:
NDV was detected by RT-PCR in 1.45% (91/6268) of samples. This percentage differed significantly according to sample type, site, species, and habitat. Sixty-three (69.23%) samples were positive for NDV and 28 (30.77%) were coinfected with AIVs. This percentage differed significantly based on the AIV subtype, with 26.37% (24/91) being H9N2-positive samples and 4.40% (4/91) being H5N8-positive samples. Results indicated that NDV isolates exhibited the characteristic cleavage site motif (112RRQKRF117) of the velogenic strains of NDV. Phylogenetic analysis of the full F gene clustered with isolates in Group I of genotype VII from Egyptian and Jordanian strains.

Conclusion:
This study highlights the need for continued surveillance of NDV genotype VII to investigate the evolution of NDV in Egypt.

Key words: Avian influenza viruses, Egypt, Newcastle diseases virus, Poultry