Parenterally transmitted hepatitis viruses are important threats to public health with Amerindians being potentially more exposed to these infections due to social and cultural habits. Viral hepatitis prevalence has been widely investigated in the Western Amazonian region of Brazil [15,16,17,18,19,20,21], but few data are available for the Eastern Amazon region [22, 23], principally in the state of Tocantins. In the present study, new data about HBV, HCV and HDV prevalence were obtained from Eastern Amazon and low prevalence of HBsAg, anti-HCV and anti-delta was observed in these individuals, showing a low risk of transmission of these viruses in this region.
Overall HBsAg prevalence was 0.4%, lower than reported in a previous study from Eastern Amazon (2.88%) , and hemodialysis individuals from Tocantins state (4%) . HBsAg prevalence was slightly higher in Amerindians (0.3%) when compared to non-Amerindians (0.1%), but this prevalence is still lower than observed in Amerindians from other localities of the Amazon Region, such as the states of Xingu, Pará and Acre, where prevalence varies from 3.3 to 14.4% [7, 17, 22, 25]. Some authors reported that sociocultural factors such as population density, scarification, tattoos and sexual activity represent important factors in the transmission of HBV [8, 26, 27]. It is possible that the infrequency of these factors among Amerindians from Tocantins may explain their low HBV prevalence compared to other Amerindians from Amazon.
HBV cleared infection was observed in 14.5% of individuals and it was higher among Amerindians and individuals more than 40 years of age. Anti-HBc prevalence varies from 40.7 to 84.7% among Amerindians from Eastern Amazon region [7, 22, 23] and 19.7 to 95.7% among Amerindians from Western Brazilian Amazon [7, 17]. Anti-HBc prevalence was high among older individuals, in concordance with previous studies among non-Amerindians from Amazon region [16, 21, 23].
In the present study, 56.7% of subjects were susceptible to HBV infection and less than 50% were HBV immune, indicating that most individuals are not protected against HBV infection. Although Amerindians are a target group for HBV vaccination, only 27.2% of Amerindians demonstrated isolated anti-HBs reactivity, less than that observed among Amerindians from the Southern (71.0%) and Northern (39.6%) regions of Brazil [22, 28]. It is likely that the low anti-HBs reactivity could be due to poor knowledge about HBV vaccination as previously demonstrated in other groups from the Northern region .
Anti-HBs reactivity was irregular among distinct sites of collection where a high prevalence of HBV-immune individuals was found in downtown Tocantinopolis, Folha Grossa and Mariazinha village. This could also be explained by access to health clinics, where high HBV vaccination coverage was found in urban areas. At the time of recruitment (2011), The Brazilian Immunization Program recommended HBV vaccination for all Amerindians and for non-Amerindians newborns and children and adolescents up to 19 years of age. Additionally, the vaccination was also recommended to those at higher risk of acquiring infection such as people who use drug, health professionals, prisoners and other groups [30, 31]. In the present study, high HBV vaccine coverage was found among people aged 0–20 since HBV vaccination was implemented for this demographic.
Overall an anti-HCV prevalence of 0.8% was observed in individuals from Tocantinópolis city, lower than that observed in studies of the general population from the Eastern Amazon Region (2.2 to 5.76%) [23, 32, 33] or hemodialysis individuals from Tocantins state (13%) . However, anti-HCV prevalence was high in Amerindians (1.2%) compared to non-Amerindians (0.3%) in concordance with a previous study from the Northern region (1.4%) .
Some studies have demonstrated that sharing cutting instruments among relatives and/or neighbors is a common habit in individuals from the Amazon region [34, 35]. These cultural habits could increase the risk of transmission of parenterally acquired viruses, such as, HCV. In addition, low knowledge about hepatitis transmission  and low access to treatment service could contribute to this high prevalence.
Overall anti-delta prevalence was 0.3% and all of these individuals were Amerindians, giving a prevalence of 3.4% in this group. According to the Brazilian Health Ministry, 10 confirmed cases of hepatitis D were found in Tocantins from 1999 to 2016 giving a prevalence of 0.3% in Brazil . Previous studies did not find anti-delta antibodies in Amerindians from the Eastern Amazon Region, [22, 25] while an anti-delta prevalence of 2.9 to 7.3% was observed in the Western Amazon Region [15, 17, 21].
Of the residents in the northern Area of Tocantins state, approximately 4.4% are reported to be Amerindian, with 81% of the population living in urban areas . In the present study, 60% of participants were Amerindian and 64% reported living rurally/in villages. The main purpose of this study is to provide new insights regarding hepatitis prevalence in Amerindians living in rural areas, so a high proportion of this group was included in the study. A major limitation of the study was the type of sampling. Consecutive sampling was used due to impossibility to conduct probability sampling in this study and since the method is very cost- and time-effective. However, it is not possible to generalize the results of the survey to the entire population and there is the possibility of under- or over-representation of the population.