Objectives: Newcastle disease is one of the most devastating avian viral diseases and causes substantial economic losses in the poultry industry worldwide. Virulence of Newcastle disease virus (NDV) is mainly determined by the amino acid sequence of the fusion (F0) protein cleavage site. During the last 12 months an outbreak of Newcastle disease affected poultry flocks in most regions of Iran. This study was conducted to isolate and molecularly characterize NDV isolates obtained from the recent outbreak of broiler flocks in Northeast Iran. Materials & Methods: Many broiler flocks with various mortality ranges submitted for diagnosis, were subjected to clinical and necropsy examination. The vvNDV was suspected in most cases. A total of seven brain samples were collected and homogenized. The homogenized samples were inoculated in embryonated chicken eggs. The allantoic fluids were examined by hemagglutination (HA) assay followed by Hemagglutination inhibition (HI) assay using NDV positive sera. RNA from positive allantoic samples were extracted and subjected to reverse transcription-polymerase chain reaction (RT-PCR) using specific primers amplifying the cleavage site of fusion gene. The PCR products were sequenced and analyzed. Results & Conclusion: All seven virus isolates from flocks with viscerotropic velogenic ND presentation were positive in HA and HI assays. RT-PCR assay proved the identity of all isolates. Analysis of the deduced amino acid sequences of the F protein cleavage site showed that all recent isolates were velogenic strains. They had the amino acid sequence 111-GRRQKRF-117 in their F0 cleavage site. This investigation showed the circulation of vvNDV in broiler flocks of Northeast Iran.

Keywords