HDAg-L variants in covert hepatitis D and HBV occult infection among Amerindians of Argentina: new insights

a b s t r a c t Background: Guidelines suggest that all HBsAg-positive patients should be tested for anti-HDV IgG anti- bodies and to confirm active hepatitis D virus (HDV) infection by detection of HDV RNA by reverse transcriptase (RT) polymerase chain reaction (PCR). Objectives: The aim of this study was to determine the serological prevalence and molecular features of HDV within an Amerindian community from Argentina exhibiting positivity for HBsAg and/or anti-HBc total Ig. Study design: Forty-six plasma samples were tested for the detection of total anti-HDV antibodies by ELISA. Concomitantly, a partial RNA region coding for the delta antigen (HDAg) was amplified by RT- nested PCR (RT-nPCR). In silica translation of DNA sequences into the amino acid (aa) sequence of HDAg-S (aa110-195) and HDAg-L (aa110-214) was performed. Results: Out of 46 HDV non-reactive samples by ELISA, 3 were HDV RNA positive by RT-nPCR. These samples were anti-HBc-only positive, 2 of them identified as cases of occult hepatitis B infection (OBI). The 3 cases were HBeAg-negative and showed normal ALT/AST levels. All sequences were ascribed to HDV genotype 1, but exhibited nucleotide differences in HDAg-L coding region, among which, mutations at codons 197 and 201 - reportedly known to promote in vitro an unsuitable interaction with HBsAg - were observed. Conclusions: These results provide evidence of covert HDV infection even among OBI, highlighting the need to reevaluate the currently applied guidelines for HDV diagnostic algorithms, as well as to explore if the observed mutations promote any effect on HDV pathogenesis. © 2012 Elsevier B.V. All rights reserved. 1. Background HDV is a defective virus that requires the helper function of hep- atitis B virus (HBV) for its assembly and transmission. 1 The HDV particle consists of an outer envelope of HBV surface proteins, while the genomic RNA is associated with two isoforms of the delta anti- gen, HDAg-S and HDAg-L. The HDAg-S plays an essential role in transactivating the replication of the HDV RNA, while HDAg-L inter- acts with HBsAg in the assembly of HDV and is a dominant repressor of HDV RNA replication. 2