Subgenotype VII.1.1 Newcastle Disease Virus Evolution and Spread in the Russian Federation in 2019-2023

Between 2019 and 2023, 163 cases of subgenotype VII.1.1 Newcastle disease virus infection were registered in backyard poultry in the Russian Federation within the framework of epizootiological monitoring. Subgenotype VII.1.1 Newcastle disease virus was reported in a total of 18 different subjects of the Russian Federation. Most of the Newcastle disease outbreaks caused by the viruses of this subgenotype occurred in the autumn and winter period (60%). Further tests allowed for the determination of complete F and HN gene nucleotide sequences for 40 isolates. The results were used to perform the Bayesian analysis of F gene sequences with BEAST v.1.10.4 software. The obtained nucleotide substitution accumulation rates were practically non-dependent on the selected nucleotide substitution model and varied appreciably depending on the applied molecular clock model (0.0018 and 0.002 site-1year-1). The conducted study established that the formation of the 'Russian' NDV isolates of subgenotype VII.1.1 followed several stages. In the early 2000s, ancestral viruses belonging to subgenotype VII-d were detected in the Middle East and Eastern Europe. From these, through intermediate forms identified in Iraq around 2007-2008, a group designated as subgenotype VII-L emerged. This group gave rise to two sister clades: the Iranian subgenotype VII-L and the cluster of isolates from Russia and Poland, whose immediate common ancestor likely existed around 2015-2016, probably in Asia.