The human T-lymphotropic virus type 1 (HTLV-1) causes a persistent infection in an estimated 5–10 million people globally, leading to various clinical manifestations. These range from severe conditions like adult T-cell leukemia/lymphoma (ATLL) to HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and other inflammatory diseases (1). Regarding HTLV-2, it is estimated that 800,000 people globally are infected with this virus, which is prevalent in people who inject drugs and American indigenous populations, particularly in Amazon region of Brazil (2, 3). Although HTLV-2 has been associated with rare cases of myelopathy, its pathological role is still unclear (4, 5). Despite these clinical and epidemiological differences, both viruses are transmitted by unprotected sexual intercourse, injecting drug use or transfusion/transplantation of contaminated blood/tissue or organ, and from mother to child, mainly through breastfeeding (1, 5).

There are more than 10.77 million people living in prison worldwide, and the world prison population may well be in excess of 11.5 million (6). Brazil has the third largest prison population in the world (835,643 in December 2022) (7). Incarcerated individuals frequently endure precarious conditions. These include overcrowded cells, inadequate ventilation and lighting, poor infrastructure, and limited access to basic sanitation. Additionally, issues like malnutrition, illicit drug use, and restricted access to health services are prevalent (8, 9), and create an environment conducive to the spread of infectious diseases (10), including bloodborne and sexually transmitted infections (STIs) (11, 12).

This study, recognizing the significant vulnerability of incarcerated individuals and the limited research on HTLV-1/2 in Brazilian prisons (13–17), aims to investigate the prevalence of HTLV-1/2 infection in Goiás State’s major penitentiary complex, Central-West Brazil, and compare these findings with prevalence data and related studies from other regions in Brazil.

Table 1 details the sociodemographic characteristics of the study participants. The majority were male (83.1%), self-identified as heterosexual (93.4%), aged between 25 and 39 years (56.1%; mean age of 31.98 ± 9.69 years), and of brown ethnicity (56.2%). Nearly half were single (49.3%), with 41.4% reporting 9 years or less of formal education.

As shown in Table 2, a minority of prisoners reported receiving blood transfusions (11.8%). While a significant portion used illicit drugs (85.2%), only a small fraction (4.2%) engaged in injecting drug use. High-risk sexual behaviors were common: 75.3% reported more than 10 sexual partners in lifetime; the prevalence of vaginal, oral, and anal intercourse was 98.1, 90.4, and 78.3%, respectively; 83.9% engaged in homosexual intercourse; 77.1% had sex with drug-using partners; and 67.1% with sex workers. Condom use was infrequent or occasional for 85.4% of the participants. Additionally, 37.1% reported group sex, and 32.3% reported sex for money. A history of STIs was noted in 25.7% of participants.

Among the 910 prisoners enrolled, 3 (0.33%; 95% CI: 0.07–0.96) were repeatedly anti-HTLV-1/2 positive by ELISA. After confirmatory testing (LIA), two were positive for HTLV-1 (0.22%) and one was positive for HTLV-2 (0.11%). The distribution of anti-HTLV-1/2 by gender revealed a higher seroprevalence among female prisoners (1.3%; 2/154) than among male prisoners (0.13%; 1/756). None of the seropositive individuals reported symptoms associated with HTLV-1/2 infection at the time of interview.

Regarding the seropositive individuals, detailed in Table 3, the two HTLV-1 positive cases included a 55-year-old male (PLG-440) and a 21-year-old female (PLG-611), both reporting unprotected sexual intercourse with multiple partners and a history of STIs. The HTLV-2 positive case, a 69-year-old female (PLG-240), had unprotected intercourse only with her sole partner and a notable history of being breastfed for over 6 months by her mother and three other women. None of the seropositive individuals reported blood transfusions or injecting drug use. In addition, one HTLV-1 positive case (PLG-611) was co-infected with HIV-1, and there were no HTLV-HBV or HTLV-HCV coinfected participants.

This study, the second to focus on HTLV-1/2 infection in Central-West Brazil’s prison population, addresses a critical issue in a strategic region. This region’s borders with other Brazilian states, Bolivia, and Paraguay make it a pivotal area for drug trafficking and criminal activities (18). In addition, our data were compared with the limited data available from other Brazilian regions in order to guide prevention actions and successful control of HTLV-1/2 and other infections in prison settings.

The sociodemographic characteristics of the studied population were similar to those reported by Melo Bandeira et al. (17) in prisoners in Mato Grosso do Sul State, Central-West Brazil, such as mostly adults aged 25–39 years, males, self-reported as brown ethnicity, single, and with less than 9 years of formal education.

Few participants reported a history of blood transfusions, with most transfusions occurring after November 1993, the onset of mandatory anti-HTLV-1/2 screening in Brazilian blood banks (19). Despite widespread illicit drug use, injecting drug use was infrequent, both in this study and among other incarcerated individuals (15, 17, 20). The majority engaged in high-risk sexual behaviors, including having multiple sexual partners and engaging in various types of sexual intercourse (vaginal, oral, and anal). Relationships with drug-using partners or sex workers were also common, alongside low condom usage. A quarter of the participants also reported a history of STIs, aligning with findings from other Brazilian prison studies (15–17, 20, 21), reinforcing the alarming vulnerability of incarcerated people to STIs and the importance of screening, treatment, and prevention strategies targeting this specific population.

The observed seroprevalence of HTLV-1/2 in this study (0.33%; 95% CI: 0.07–0.96) was significantly higher than the rate among local blood donors (0.09%) (22). Nevertheless, relative to other Brazilian prison populations (Table 4), this prevalence was similar to that estimated in prisoners in Mato Grosso do Sul State (0.40%; CI 95%: 0.15–0.87) (17) and falls within the confidence interval reported for incarcerated adolescents in Salvador, Bahia (1.01%; CI 95%: 0.21–2.92) (16). In prior studies, however, Broutet et al. (13) observed a higher seroprevalence (1.41%; CI 95%: 0.52–3.03) in Fortaleza, Ceará. Also, Catalan-Soares et al. (14) determined a seroprevalence of 1.59% (95% CI: 0.04–8.53) among male prisoners in Manhuaçu, Minas Gerais, in a study that included a smaller number of participants.

Internationally, the HTLV-1/2 seroprevalence in this study was lower than those reported among specific groups of prisoners, such as male inmates in Maryland, USA (0.93%; CI 95%: 0.55–1.47) (23), HIV-infected inmates in Mozambique (1.55%; CI 95%: 0.67–3.04) (24), immigrants in prison in Italy (2.52%; CI 95%: 1.09–4.91) (25), and prisoners in Tijuana, Mexico (7.07%; CI 95%: 4.79–10.00) (26), but a study in a Danish prison reported no cases of HTLV-1/2 infection (27), indicating varied prevalence rates among prisoners globally.

The distribution of HTLV-1/2 infection by gender showed a higher seroprevalence among female prisoners, which was consistent with that reported in Mozambique (24), possibly reflecting the more efficient transmission of virus from male to female during sexual intercourse (28). On the other hand, this finding differs from previous reports in Brazil which found a higher prevalence of HTLV-1/2 in male prisoners, possibly reflecting their high-risk behaviors (16, 17).

In the major penitentiary complex of Goiás State, we detected anti-HTLV-1 (0.22%) and anti-HTLV-2 (0.11%). This finding aligns with previous research in Fortaleza, Ceará, where anti-HTLV-1 (0.47%) and HTLV-2 (0.47%) were found among prisoners (13). More recently, Melo Bandeira et al. (17) also found the presence of HTLV-1 (0.20%) and HTLV-2 (0.13%) in people living in prisons in Mato Grosso do Sul. Relative to other studies on HTLV-1/2 infection in Goiás, HTLV-1 and 2 dual infections were observed only in patients with pulmonary tuberculosis (29), a population among whom one quarter reported previous incarceration.

Both HTLV-1 seropositive prisoners (PLG-440 and PLG-611) reported unprotected sex with multiple partners and history of STIs. These risky sexual behaviors may contribute to the observed seropositivity for this infection among the studied population since unprotected sexual intercourse and a higher number of partners increase the risk of HTLV-1 transmission (1, 28, 30). In addition, one of these individuals (PLG-611) was co-infected with HIV-1. As HTLV-1 and HIV-1 share common transmission routes, co-infection can occur in endemic areas, as reported in other prison populations (17, 24, 25).

Additionally, two seropositive individuals, one with anti-HTLV-1 (PLG-440) and the other with HTLV-2 (PLG-240), reported being breastfed during childhood. Notably, PLG-240 was breastfed for over 6 months by her mother and three other women in Piaui State, a detail that aligns with findings from a previous study on blood donors and their families in Piaui, where long-term breastfeeding during childhood was linked to HTLV-1/2 infection (31). In fact, HTLV-1/2 is transmitted primarily through infected bodily fluids including breast milk (1, 5). As reported elsewhere (32–34), it is important to note cross-breastfeeding as a potential risk to transmit HTLV-1/2 infection in addition to mother-to-child transmission. Therefore, implementing antenatal screening for HTLV-1/2 and interventions to limit or avoid breastfeeding by women living with HTLV-1/2 are essential to prevent the spread of this infection in endemic regions.

This study has some limitations. First, all interviews were performed face-to-face; therefore, some findings are subject to response biases, especially those regarding sexual behaviors/practices, illicit drug use, etc. Otherwise, some strategies were used to minimize potential biases, including previously trained interviewers and a private place for interviews in each unit of the Prison Complex of Aparecida de Goiânia. Also, the exclusion of individuals who appeared to be under the influence of psychotropic drugs from the study may bias the results potentially underestimating the prevalence; however, only a few prisoners were excluded considering this criterion. Due to health restrictions imposed by the COVID-19 pandemic, it was not possible to collect another blood sample from the three anti-HTLV-1/2 positive individuals for HTLV proviral DNA detection, and ultimately the seropositive individuals were transferred to other cities. Despite these limitations, this study provides valuable epidemiological information on HTLV-1/2 in an incarcerated population in Central-West Brazil.

This study revealed a relatively low seroprevalence of HTLV-1/2 infection in the major penitentiary complex of Goiás State, Central-West Brazil. Importantly, it also indicated the presence of HTLV-1 and HTLV-2 in this setting. The prevalence of high-risk behaviors, particularly sexual behaviors, and the interactions of incarcerated individuals with the external community, underscore the critical need for targeted programs in prisons. These programs should focus on the diagnosis, control, and prevention of HTLV-1/2 and other STIs.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by Research Ethics Committee of the Clinical Hospital, Federal University of Goiás. The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation in this study was provided by the participants' legal guardians/next of kin.

MO: Conceptualization, Writing – review & editing, Methodology. MaM: Conceptualization, Methodology, Writing – review & editing. NF: Methodology, Writing – review & editing, Formal analysis. ÁS: Methodology, Writing – review & editing. JM: Methodology, Writing – review & editing. TM: Methodology, Writing – review & editing. MáM: Writing – review & editing, Conceptualization, Writing – original draft. RM: Conceptualization, Writing – original draft, Writing – review & editing, Supervision.