Human retroviruses were identified about four decades ago. Human T-cell lymphotropic virus type-1 (HTLV-1), identified four years before the successful isolation of human immunodeficiency virus (HIV), was the first human retrovirus associated with the clinical development of disease (1, 2). HTLV-2 was isolated in 1982 and is rarely associated with disease manifestations (3). With approximately 10 million people infected worldwide, despite the advances made in the scientific understanding of this viral infection, HTLV-1 and its associated diseases remain extremely neglected (4, 5). Most geographic regions affected by this virus, except Japan, are classified as middle- or low-income, and infected persons possess low levels of education and income (6). The geographic regions in which HTLV-1 is primarily endemic are Japan, the Caribbean, South and Central America, Equatorial Africa, the Middle East, Melanesia, and Australia. Brazil is considered the country with the highest absolute number of people (approximately one million) living with HTLV-1 (PLHTLV) (7, 8).The first Brazilian cases of HTLV-1 infection were detected in 1986 in the state of Mato Grosso do Sul (9). Several studies conducted by Brazilian researchers have reported that infection is prevalent throughout the national territory, with higher prevalence noted in the north and northeast regions (10, 11). In Bahia, there is strong evidence supporting multiple post-Columbian introductions of HTLV-1 during the slave trade between the 16th and 19th centuries (12–15). This state also has the highest prevalence of HTLV-1, with nearly 130,000 PLHTLV (16). In the city of Salvador, the state capital, a general population study estimated 40,000 HTLV-1-infected individuals, corresponding to a prevalence of 1.7% (13). This study also found that prevalence increases with age, reaching 8.4% in those aged over 51 years, and noted a higher prevalence in individuals with lower income, less education, and poorer living conditions (13). Sexual transmission appears to be the predominant route of HTLV-1 infection in Salvador (17).

Efforts by Brazilian scientists have contributed to a better understanding of the epidemiology, clinical and laboratory aspects as well as pathogenesis of this infection, thereby raising awareness of HTLV-1 as a serious public health problem in Brazil (18). Although screening for HTLV-1 at blood banks became mandatory in Brazil since 1993 (19), only recently has the WHO/PAHO considered HTLV-1 infection to be a serious health problem, prompting the Brazilian Ministry of Health to implement additional measures to control infection (20, 21).

It is important to note that while there is no cure or  effective vaccine for HTLV-1 infection, pharmacological and nonpharmacological treatments help minimize patient suffering and improve the quality of life (QoL) of this neglected population. Furthermore, while additional public health measures are required to prevent and/or control the spread of HTLV-1 infection, health care provisions for patients also remain a challenge (22, 23).