Seroprevalence of the Human T Lymphotropic Virus (HTLV 1 and HTLV 2) in Blood Donor Candidates in the State of Pará, Northern Brazil

The present study describes HTLV seroprevalence in potential blood donors from the Brazilian state of Pará, and the sociodemographic characteristics of the infection in this state. This descriptive, retrospective, and cross-sectional study is based on secondary serological and sociodemographic data on potential blood donors who were rejected for presenting reactive results in the serological HTLV screening between January 2010 and December 2020. The mean HTLV seroprevalence was 0.2%. The highest frequency of reactivity was recorded in first-time donors, women, individuals over 30 years old that were single and had a relatively low level of education. There have been many advances since the discovery of HTLV, although it is still considered to be a neglected etiological agent in Brazil. Further research on data from hematological services will be necessary to refine regional infection profiles, which will be fundamental for the development of adequate prophylactic practises to control and prevent infection, as well the dissemination of information on the dangers of HTLV to the general population.


Introduction
The human T lymphotropic virus (HTLV) is a retrovirus of the genus Deltaretrovirus, family Retroviridae (ICTV, 2022). This virus presents tropism for T lymphocytes, and has four types, HTLV-1, HTLV-2, HTLV-3, and HTLV-4, of which, the first twotypes 1 and 2are the most pathogenetic and thus the most relevant in epidemiological terms. Type 1 HTLV infects primarily the CD4+ T lymphocytes, and most carriers remain asymptomatic throughout their lives. This infection is linked to serious diseases such as Tropical Spastic Paraparesis/Myelopathy associated with HTLV-I (TSP/HAM), and disorders such as infectious dermatitis, Sjogren syndrome, and uveitis (Semeão et al., 2015;Martinez et al., 2019). Type 2 HTLV infects primarily the CD8+ T lymphocytes, and it is not typically associated with any specific disease (Martinez et al., 2019;Futsch et al., 2017;Schierhout et al., 2020).
Both HTLV-1 and HTLV-2 are transmitted via the sexual route, most commonly from men to women, and are associated with unprotected sex, multiple sexual partners, and the presence of genital wounds or ulcers (Bandeira et al., 2017;Nunes et al., 2017;Pereira & Bonafé, 2015). Vertical transmission, which is the most frequent route of infection in endemic areas, occurs mainly through breastfeeding, with the probability of infection increasing with the duration of breastfeeding, given the cumulative risk of exposure to HTLV in the mother's milk, and the declining levels of neutralizing antibodies in the infants over time (Percher et al., 2016;Rosadas & Taylor, 2019). The most efficient transmission route is the parenteral one, however, through the transfusion of contaminated blood or the sharing of needles by intravenous drug abusers, although the screening of blood banks should control the transmission via this route in endemic areas (Eusebio-Ponce et al., 2019;Ngoma et al., 2019).
It is estimated that between five and 10 million people are infected with HTLV-1 worldwide, with the highest rates of prevalence being found in Japan, the Caribbean, South America, and Sub-Saharan Africa, with some foci in the Middle East and Oceania (Gessain & Cassar, 2012). In Brazil, the number of individuals infected with HTLV-1 is estimated to be approximately 2.5 million, although its seroprevalence varies considerably according to sociodemographic factors, the geographic region, and individual risk-taking behavior. Specifically, the prevalence of HTLV-1 is lowest in southern Brazil, while the highest rates are found in the north and northeast of the country Mendes et al., 2020).
The northern state of Pará has the third highest rate of HTLV infection in Brazil (14) . Prevalence studies of specific groups (e.g., blood donors, intravenous drug users, pregnant woman) have confirmed the presence of HTLV throughout the country Morais et al., 2017;Costa et al., 2018;Guerra et al., 2018).
Hemotherapy centers have focused increasingly on the development and use of new technologies for the reduction of the the risks of transfusion, especially for the prevention of the transmission of infectious agents. Screening for HTLV-1 and HTLV-2 became mandatory for Brazilian blood banks in 1993, based on federal ordinance number 1376 emitted by the Ministry of Health (Pereira & Bonafé, 2015).
Given the high rates of HTLV seroprevalence found in potential blood donors in Pará, the relative ease of transmission of HTLV via blood transfusion, and the high morbidity of the associated disease, it will be essential to compile an accurate database on the epidemiology of HTLV through which effective prophylactic practises can be established. The variation in HTLV seroprevalence found among the different Brazilian regions emphasizes the need for the systematic understanding of the underlying socioeconomic, demographic, and cultural determinants, in order to design adequate procedures for the monitoring and control of HTLV infection in Brazilian populations.
In this context, the present study determined the seroprevalence of the human T lymphotropic virus types 1 and 2 in potential blood donors at the Pará State Hemotherapy and Hematology Center (HEMOPA) -the state's reference hematological institution -over the past 11 years. The data were used to evaluate the sociodemographic characteristics of the virus in the population of Pará.
The present study is descriptive, retrospective, and cross-sectional, and was based on the analysis of secondary serological data collected during the screening of potential blood donors, in particular, the rejection of donor candidates based on reactive or inconclusive results in the serological test for HTLV. These data were collected between January 2010 and December 2020. The dataset analyzed here included all the candidates for blood donation that presented reactive or inconclusive results for HTLV-1/2 in the serological screening.
Up until July 2014, HEMOPA screened potential blood donors using the MUREX HTLV I+II test, which is based on the ELISA procedure. In August 2014, HEMOPA adopted the chemiluminescence microparticle assay (CMIA), using the ARCHITECH rHTLV-I/II platform, which continued until December 2019. As of January 2020, screening for HTLV-1/2 has been based on electrochemiluminescence, using the Elecsys HTLV-I/II system. These screening tests are based on the detection of antibodies in the serum or plasma.
The data analyzed in the present study were obtained from the HEMOPA online Blood Bank system (SBS and Progress) and transferred to a database in the Statistical Package for Social Sciences (SPSS), version 26. This database included information on the gender, age, geographic origin, education level, marital status, ethnic heritage (as self-reported by the donor), the type of donor, number of donations, and the qualitative and quantitative results of the serological tests.
The qualitative variables are presented here as absolute and relative frequencies. The quantitative variables are presented through measures of central tendency (mean or median) and variance (standard deviation and amplitude), with the exact parameters used being determined by the characteristics of the variable.
The present study was approved by the research ethics committee, under CAAE protocol 45084121.5.0000.5701, in accordance with the Helsinki declaration of 1975. As the study uses only secondary data, informed consent was not required, as no individuals were identified, and confidential information was not disclosed in any case. All the authors of the present study agreed to use the data only for the purposes of this study, and complied with all the guidelines and regulatory standards on data confidentiality outlined by resolution 466/12 of the Brazilian National Health Council (CNS) and its complements.    The sociodemographic characteristics of the potential HEMOPA blood donors that were reactive for anti-HTLV-1 and HTLV-2 are shown in Table 1. The mean age of these donors was 33.12±11.301 years (amplitude: 16-68 years of age), with a majority of individuals (1018; 40.0%) in the youngest age class, 16-29 years of age (Table 2).

Discussion
No systematic epidemiological studies of the prevalence of HTLV are available for the general population of Brazil, although studies of blood donors do provide some insights into infection rates. The seroprevalence of this virus in blood donors varies considerably among Brazilian states (Figure 2), with the highest prevalence typically occurring in the North (Acre, Amazonas, Amapá, Pará, Rondônia, Roraima, and Tocantins states) and Northeast (Alagoas, Bahia, Ceará, Maranhão, Paraíba, Pernambuco, Piauí, Rio Grande do Norte, and Sergipe) (Semeão et al., 2015;Catalan-Soares et al., 2005;Morais et al., 2017;Galvão-Castro et al., 1997;Ribeiro-Lima et al., 1999;Maneschy et al., 2021;Silva & Silva, 2015;Ribeiro et al., 2018), while the lowest rates are found in the South (Paraná, Rio Grande do Sul, and Santa Catarina) and Southeast (Espírito Santo, Minas Gerais, Rio de Janeiro, and São Paulo) regions (Semeão et al., 2015;Pereira & Bonafé, 2015;Catalan-Soares et al., 2005;Galvão-Castro et al., 1997;Veit et al., 2006). In previous studies, the HTLV seroprevalence in potential blood donors from the state of Pará ranged from 0.3% (Maneschy et al., 2021)  The observed variation in the HTLV seroprevalence in the state of Pará can be accounted for by a number of factors, such as the study period, the size of the study population, and shifts in the behavior of the population. The study period may have been an important factor that influenced the seroprevalence rates, since previous studies by Ribeiro Lima et al. (1999), Maneschy et al. (2021) and Catalan-Soares et al. (2005) were relatively short-term, spanning two, five and six years, respectively, in comparison with 11 years in the present study, which may have provided a more realistic estimate of the seroprevalence of the donor population of Pará. The different methods of serological screening used during the respective study periods may also have influenced the results, given that the sensitivity and the specificity of the tests vary according to the approach, the antigens used, and the class of antibodies detected by the procedure (Maneschy et al., 2021). Increasing knowledge on the risks and prevention of sexually transmitted infections may also have contributed to shifts in the behavior of the population over time.
Although the highest frequency of HTLV reactivity was among female donors, a very close percentage of males was demonstrated, which goes against what has been described by studies that indicate the infection is strongly linked to the female sex. The average age of approximately 33 years is similar to that of other studies that relate infection to advancing age (Gessain & Cassar, 2012;Maneschy et al., 2021;Eshima et al., 2009). This is related to the greater efficiency of transmission from men to women and the greater number of sexual exposures throughout life (Glória et al., 2015;Silva et al., 2018). The predominance of single (including divorced and widowed) individuals recorded in the present study may be related to a greater risk of sexual transmission associated with multiple partners and unprotected sex Silva & Silva, 2015;Proietti et al., 2005). Donors with high school completed were more frequent for HTLV seropositivity, which may be a reflection of the reduced access to information on basic health, in general, and on the prevention of sexually transmitted infections, in particular (Glória et al., 2015;Dourado et al., 2003).
Many potential blood donors may believe that blood banks are a convenient place for free medical testing, and thus avoid revealing their risky behavior during clinical screening. This may have contributed to the predominance of first-time donors in the study samples. Regular donors, who are tested every time they donate blood, are a probably low-risk group for HTLV infection (Pereira & Bonafé, 2015;Morais et al., 2017;Maneschy et al., 2021;Blatyta et al., 2013). Almost two-thirds of the reactive samples were from the metropolitan area of Belém (the Pará state capital), and more than three-quarters were from individuals that self-identified as being of mixed heritage (Table 1). More than two-thirds of the samples were obtained from spontaneous donors.

Conclusion
The present study demonstrated a HTLV seroprevalence of 0.2% in potential blood donors from the Brazilian state of Pará, who were screened over a period of 11 years. This prevalence is likely similar to the actual level found in the state's population. In previous studies, a greater prevalence of HTLV has been found in unmarried women, individuals over the age of 30, and first-time donors with a second level of education, which is approximately consistent with the epidemiological profile recorded in the present study.
There have been many advances since the discovery of HTLV, although it is still considered to be a neglected etiological agent in Brazil, which is still poorly known, not only by the general population, but also by healthcare professionals. As no study has yet provided any reliable estimate of the actual prevalence of the virus in Brazil, the analysis of blood donor data provides an important means of assessing the epidemiological profile of a given region, which should contribute to the development of adequate prophylactic practises and the dissemination of knowledge on HTLV infection.