GENETIC CHARACTERIZATION OF EGYPTIAN NEWCASTLE DISEASE VIRUS STRAINS ISOLATED FROM FLOCKS VACCINATED AGAINST NEWCASTLE DISEASE VIRUS, 2014-2015

In the present study, forty-five chicken flocks suspected to be infected with Newcastle disease virus (NDV) in Sharkia Governorate were submitted for clinical and postmortem examination as well as virus isolation and sero-molecular identification. Forty samples were positive for hemagglutinating viruses, 15/40 (37.5%) were confirmed positive isolates against NDV antiserum, 12/40 (30%) were positive isolates against both NDV and AIV (H5) antisera and 9/40 (22.5%) were positive against AIV antiserum using serological identification. Twenty-seven NDV isolates were confirmed positive by molecular identification; twelve of them were confirmed as virulent NDV strains using specific primers. A fragment of 766-bp comprising the 3' end of the M gene and the 5' end of the F gene was sequenced from four amplified products, revealing that these isolates carried the 112RRQKRF117 motif, which is characteristic of virulent strains. The investigated strains were clustered with a class II genotype VIId with large genetic distance with the LaSota strain. This is alarming given the potential evolution of different virulent NDVs and may explain the circulation of these virulent strains among Egyptian poultry farms despite the application of intensive vaccination programs.