Evolution of Newcastle disease virus subgenotype VII.1.1 in Iran, 2017-2024

Newcastle disease (ND), caused by Newcastle disease virus (NDV), has posed a continuous threat to Iran's poultry industry since its first detection in the early 1950s, with subgenotype VII.1.1 currently recognized as the dominant circulating strain. To gain deeper insights into the evolutionary dynamics of NDV in Iran, we performed genome sequencing and phylogenetic analysis on 60 viruses isolated from domestic poultry and wild birds between 2017 and 2024. Maximum likelihood and Bayesian phylogenetic analyses of the fusion (F) and haemagglutinin-neuraminidase (HN) genes revealed that all viruses belong to subgenotype VII.1.1, forming a well-supported monophyletic group, indicative of independent evolution of this subgenotype within Iran after its introduction. The F and HN genes displayed high sequence identities of over 97% and 93%, respectively. All viruses contained a polybasic cleavage site in the F gene (R-R-Q/K-K-R↓F), consistent with virulent NDV strains. The estimated evolutionary rates for the F and HN genes were 1.31 × 10^-3 and 9.62 × 10^-4 substitutions/site/year, respectively. The most recent common ancestor of the subgenotype VII.1.1 F gene was dated to 2007 (95% highest posterior density: 2005-2009), likely originating from the Middle East. Bayesian skyride analysis showed an exponential increase in viral diversity between 2020 and 2024. Continuous surveillance of NDV in both poultry and wild birds in Iran is essential to track ongoing viral evolution, monitor potential changes in virulence or transmissibility, and identify emerging threats to poultry health and production.