First detection and characterisation of sub‐genotype XIII.2.1 Newcastle disease virus isolated from backyard chickens in Iran

Background: Newcastle disease (ND) is an economically significant poultry disease worldwide. During field surveillance for ND in 2010 in Iran, a backyard chicken flock showed clinical signs of ND with 100% mortality. Objectives: We aimed to characterise genetically, biologically and epidemiologically an exotic virulent ND virus (NDV) detected in Iran. Methods: After observing high mortality, dead birds were sampled and then disposed of by burial, and the chicken house was disinfected. Tissue samples were molecularly tested for NDV. The genetic homogeneity of the isolate RT30/2010 was tested by plaque assay, and then a large virus plaque was used for the second step of plaque purification. Fusion and matrix complete genes were sequenced and used for genotyping and epidemiological tracing. We tested biological pathotypes using mean death time (MDT) and intracerebral pathogenicity index (ICPI) assays. Results: The isolate formed heterogeneous plaques in chicken embryo fibroblast cells. The second step of plaque purification produced homogeneous and large plaques. Phylogenetic analysis using both genes classified the virus into sub-genotype XIII.2.1. Nucleic acid and amino acid identities of RT30/2010 fusion gene with the closest available isolate SPVC/Karachi/NDV/43 are 97.95% and 98.73%, respectively. Isolate has 112 RRRKRF 117 motif at the fusion cleavage site, and pathogenicity tests showed MDT of 56.4 h and ICPI of 1.85. Conclusions: This study presents the first detection and characterisation of a velogenic NDV of sub-genotype XIII.2.1 from Iran. Our follow-up surveillance for ND shows that timely virus detection and carcass management have led to the cessation of virus transmission in Iran.