Human T-cell Lymphotropic Virus Type 1 (HTLV-1) is a human retrovirus that causes mainly asymptomatic chronic asymptomatic infection (Umekita and Okayama, 2020). Although normally asymptomatic, infected individuals can still be active viral reservoirs and, consequently, cause transmission (Bandeira et al., 2021).

HTLV-1 diagnosis is performed initially with screening tests by enzyme immunoassays (EIA), such as Enzyme-Linked Immunosorbent Assay (ELISA), or chemiluminescence immunoassay (CLIA) (Brazil, 2022). CLIA uses a luminescent molecule instead of an enzyme, which implies an easier workflow and a wider range of detection (Cinquanta et al., 2017). In addition, CLIA has been widely used for anti-HTLV screening (Guiraud et al., 2023). After the screening test, HTLV infection diagnostic confirmation can be performed using western blotting and molecular assays, which are based on proviral DNA detection (Brazil, 2022). However, molecular diagnosis by polymerase chain reaction (PCR) is highly complex and expensive. Overall, this system yields a high rate of inconclusive and false-negative results, in addition to requiring highly trained professionals and expensive equipment and reagents (Caterino-de-Araujo et al., 2021).

Because of the high rate of asymptomatic patients, it is most likely that the number of individuals infected is highly underestimated (Bangham et al., 2015). As a result, non-endemic countries are already implementing the HTLV-1 screening system on donor banks, like Spain (de Mendoza et al., 2017), which is showing that prevalence for HTLV-1/HTLV-2 is higher than previously thought worldwide. Furthermore, the silent intrafamilial transmission of HTLV is common in this disease, by both sexual and vertical pathways (Silva et al., 2023). Those factors highlight the need for sensible and easy screening methodologies.

Plasma viremia is not significant in HTLV infection, which might difficult the molecular diagnosis in cell-free biological fluids (Demontis et al., 2015). Given this, dried blood spot (DBS), which is a collection of blood samples on filter paper, might be an important alternative for HTLV-1 diagnosis since the blood volume required is less compared to conventional venipuncture, and blood collection is simple and noninvasive (Gupta and Mahajan, 2018).

Considering the disadvantages of PCR-based assays, loop-mediated isothermal amplification (LAMP), first developed by Notomi et al., (2000), might be a rapid and cost-effective alternative nucleic acid test which is characterized by target amplification under isothermal conditions (Mori and Notomi, 2009). This method is characterized by a DNA polymerase with strand-displacement activity, along with inner and outer primers that form cycling loops. LAMP assays have been successfully applied to the detection of RNA viruses, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (da Costa et al., 2023) and human immunodeficiency virus-1 (HIV-1) (Curtis et al., 2009).

In this study, we evaluated the use of serological (CLIA) and molecular (LAMP) methods for HTLV-1 detection in alternative blood samples.