High prevalence of hepatitis B virus subgenotypes A1 and D4 in Maranhão state, Northeast Brazil

Highlights

• The prevalence of HBV subgenotypes in northeastern Brazil was determined.

• HBV subgenotypes A1, D2, D3, D4 and F2a were found.

• HBV/A1 was the most prevalent.

• HBV/D4 was found more frequently than in other Brazilian regions.

• HBV strains circulating in different regions of Brazil show a great genetic variability.

Abstract

In this study, we determined the prevalence of HBV subgenotypes in Maranhão state, located in northeastern Brazil, where the population is heterogeneous, with a high proportion of African descendants. HBV was detected in 119 of 133 (89.5%) chronic hepatitis B patients, including 103 (86.5%) who were HBeAg-negative. Using phylogenetic analysis of the S/Polymerase region of HBV DNA, subgenotype A1 was found to be the most prevalent (67%), followed by genotype D (28%; subgenotype D4 was detected in 24%, D3 in 3%, and D2 in 1%). Genotype F, clustering with subgenotype F2a, was found in six (5%) patients. The topology of the phylogenetic tree showed that HBV/A1 sequences did not cluster together, suggesting that more than one strain was introduced into Maranhão. On the other hand, HBV/D4 sequences formed a monophyletic cluster, suggesting a single entry of this strain in this population. This study showed that HBV/A1 was the only subgenotype of HBV/A present in the population from Maranhão and indicated that in this region HBV/A1 was not restricted to an Afro-descendant community where it was previously reported, but is widely distributed among general population of HBV chronic carriers.

Unexpectedly, we found a high frequency of HBV subgenotype D4. Together with previously reported data on the distribution of HBV/D4 in the world, these findings suggest that this subgenotype was more prevalent in the African continent in the past and may have been introduced in Maranhão by means of the slave trade during the late XVIII century, when the largest number of African slaves arrived to this region.

Introduction

Globally, the prevalence of chronic hepatitis B (CHB) varies considerably, with areas of high (>8%), intermediate (2–7%) and low (<2%) endemicity (WHO, 2002). A recent epidemiological study, carried out among a representative sample of the Brazilian population showed an HBsAg prevalence of less than 1% in Northeast and Central-West regions (Pereira et al., 2009). However, in other regions, including some areas of the Amazon, south and southwest regions, hepatitis B virus (HBV) infection is hyperendemic and poses a serious health threat (Bertolini et al., 2006, Braga et al., 2012, Souto, 1999).

Brazil is a very large country and in several areas the epidemiological picture of HBV infection is unknown, especially in smaller cities or rural communities, where large reservoirs of HBV infection may persist. Maranhão state is located in the northeastern region of Brazil, is divided in 217 counties (Fig. 1), and has a population of approximately 6,794,301 inhabitants (http://www.ibge.gov.br/estadosat/perfil.php?sigla=ma). Population from Maranhão is one of the most heterogeneous in the country, with a high proportion of African descendants. In the few epidemiological studies carried out to estimate HBV prevalence in this state, was observed that it was variable, depending on the studied group: a low HBV prevalence (0.5–0.9%) was found in two studies among the urban population from São Luís, the capital of Maranhão state (Pereira et al., 2009, Souza et al., 2012); whereas an intermediate prevalence (2.8%) was found in a rural area (Buriticupu) (El Khouri et al., 2010) and a surprisingly high prevalence (12.5%) reported in an African descendant population from another rural area (Frechal) (Alvarado-Mora et al., 2011).

HBV is currently classified into ten genotypes (A–J) based on a difference in genomic sequence of 7.5% or more and some of them have been further classified into subgenotypes (Kramvis et al., 2008, Norder et al., 2004). Most HBV genotypes and some of their subgenotypes have characteristic geographic distribution around the world and a strong correlation with ethnicity (Kramvis et al., 2008, Kurbanov et al., 2010, Norder et al., 2004). Moreover, genotypes/subgenotypes can affect the natural course of infection and response to antiviral treatment (Cooksley, 2010, Kramvis and Kew, 2005, Lin and Kao, 2011).

Knowledge of HBV genotypes/subgenotypes prevalence in a geographical region is also important to understand the routes of HBV dissemination and to establish efficient strategies to prevent and control HBV infection. Genotypes B and C have been related to vertical transmission while subgenotype A1 and genotypes D, E, F and H are more related to horizontal transmission during early childhood. HBV/A2 has been frequently involved in sexual transmission and is more prone to establish chronic disease in adults. Like HBV/A2, genotype G infection is associated with sexual transmission as a risk factor for infection and is frequently found in men who have sex with men (Araujo et al., 2011).

Genotypes A, D and F are the HBV genotypes more prevalent in Brazil (Bertolini et al., 2012, Gomes-Gouvea et al., 2009, Mello et al., 2007, Moura et al., 2013, Santos et al., 2010, Sitnik et al., 2004, Victoria et al., 2008). Although studies in particular regions of the country have shown the predominance of HBV subgenotypes A1, D3 and F2a (Bertolini et al., 2012, Gomes-Gouvea et al., 2009, Mello et al., 2007, Moura et al., 2013, Santos et al., 2010, Victoria et al., 2008), this information remains poorly understood in most of Brazilian regions. Specifically in Maranhão state, there is just one study that characterized the distribution of HBV subgenotypes in an Afro-descendant community where only HBV/A1 was identified (Alvarado-Mora et al., 2011), however the extent of its distribution in this state is unknown.

The aim of this study was to characterize the HBV genotypes and subgenotypes in chronic hepatitis B carriers from different regions of Maranhão state and to relate this data with demographic and clinical features of the patients.