Phylogenetic and Mutational Analysis of the Tax Gene in the Human T-Lymphotropic Virus 1 (HTLV-1) in Three Provinces of Iran

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.