Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 54 12 2025 12 31 Phylogenetic and Mutational Analysis of the Tax Gene in the Human T-Lymphotropic Virus 1 (HTLV-1) in Three Provinces of Iran 2764 2772 Bezhan Noori 1. Department of Virology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran 2. Department of Infectious Diseases and Tuberculosis, Kabul Medical University of Sciences, Kabul, Afghanistan Atefeh Bahavar Department of Microbiology and Virology, School of Medicine, Alborz University of Medical Sciences, Karaj, Iran Zohreh Sharifi Blood Transfusion Research Center, High Institute for Research and Education in Transfusion Medicine, Tehran, Iran Parnaz Kafialqora Student Research Committee, Alborz University of Medical Sciences, Karaj, Iran Zahra Navi Urology Research Center, Tehran University of Medical Sciences, Tehran, Iran Abbas Rahimi Foroushani Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Mohammadreza Shafiei Student Research Committee, Alborz University of Medical Sciences, Karaj, Iran Seyed Mohammad Jazayeri 1. Department of Virology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran 2. Research Center for Clinical Virology, Tehran University of Medical Sciences, Tehran, Iran Sayed-Hamidreza Mozhgani 1. Department of Microbiology and Virology, School of Medicine, Alborz University of Medical Sciences, Karaj, Iran 2. Research Center for Clinical Virology, Tehran University of Medical Sciences, Tehran, Iran Mehdi Norouzi Department of Virology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran 2025 05 26 2025 10 19 Background: Human T-lymphotropic virus type 1 (HTLV-1) is considered a health issue in Iran. However, its genetic diversity and molecular epidemiologic phylogeny remain poorly characterized. Methods: The Tax gene of 9 asymptomatic individuals across Alborz, Gilan, and Ardabil provinces of Iran was sequenced and analyzed phylogenetically using MEGA-X. Results: All strains clustered within the Cosmopolitan subtype a, showing high genetic similarity to Japanese and Chinese references. Positive selection (dN/dS > 1) was observed in all samples. Strikingly, the Alborz ISO32 strain exhibited 10 unique nonsynonymous mutations, suggesting regional evolutionary divergence. Conclusion: This study, as the first multi-provincial study in Iran, reveals the essential requirement for systematic tracking of HTLV-1 genetic diversity and designing prevention programs tailored to each region. https://ijph.tums.ac.ir/index.php/ijph/article/view/39283 https://ijph.tums.ac.ir/index.php/ijph/article/download/39283/8736