Nazila Ariaee - Immunology Research Center, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
Shadi Abbasnia - Immunology Research Center, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
Faezeh Sabet - Department of Microbiology and Virology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
Ali Mirhossein - Immunology Research Center, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
Sanaz Ahmadi Ghezeldasht - Blood Born Infections Research Center, Academic Center for Education, Culture and Research, Razavi Khorasan, Mashhad, Iran.
Mehdi Moshfegh - Department of Neurology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
Reza Boostani - Blood Born Infections Research Center, Academic Center for Education, Culture and Research, Razavi Khorasan, Mashhad, Iran.
Seyed Abdolrahim Rezaee - Immunology Research Center, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.

Background: The significance of HTLV-۱ proviral load as a prognostic biomarker in HTLV-۱-associated myelopathy/tropical spastic paraparesis (HAM/TSP) has been a subject of controversy. This study aims to assess the impact of HTLV-۱ proviral load (PVL) on the clinical outcome in patients with HAM/TSP. Methods: An absolute quantitative HTLV-۱ PVL RT-qPCR, TaqMan method was developed with ۱۰۰% sensitivity and specificity. Then, from ۲۰۰۵-۲۰۱۸, the HTLV-۱ PVL of ۹۰ eligible newly diagnosed HAM/TSP patients were assessed for demographic, clinical symptoms and their associations with HTLV-۱-PVL. Results: The quality control of the designed RT-qPCR showed a sensitivity and specificity of ۱۰۰%. Spasticity in lower limbs in ۵۸.۹% and urinary symptoms in ۱۷.۸% of HAM/TSPs were observed. Using this designed RT-qPCR, the HTLV-۱-PVL strongly affected spasticity and sphincter disturbance (p=۰.۰۵). The multivariate logistic test showed that only the beginning of lower limb weakness along with tremor was associated with PVL (OR: ۲.۷۸. ۹۵% CI (۰.۹۹-۱.۰۲) and p=۰.۰۵). Urinary incontinence was prevalent among these patients; however, no association was identified with the HTLV-۱ proviral load (PVL). Conclusion: The absolute RT-qPCR developed for measuring HTLV-۱ proviral load (PVL) demonstrated reliable results. Despite a high prevalence of urinary incontinence in these patients, no association was observed with the PVL. Consequently, it appears that HTLV-۱ proviral load is specifically associated with developing spasticity in HAM/TSP.

Clinical manifestations, HTLV, Neuroinflammatory disease, Proviral load, TaqMan. ​​