A divergent hepatitis D-like agent in birds

Hepatitis delta virus (HDV) is currently only found in humans, and is a satellite virus that depends on hepatitis B virus (HBV) envelope proteins for assembly, release and entry. Using meta-transcriptomics, we identified the genome of a novel HDV-like agent in ducks. Sequence analysis revealed secondary structures that were shared with HDV, including self-complementarity and ribozyme features. The predicted viral protein shares 32% amino acid similarity to the small delta antigen of HDV and comprises a divergent phylogenetic lineage. The discovery of an avian HDV-like agent has important implications for the understanding of the origins of HDV and subviral agents. Importance Hepatitis delta virus (HDV) is currently only found in humans, and coinfections of HDV and Hepatitis B virus (HBV) in humans result in severe liver disease. There are a number of hypotheses for the origin of HDV, although a key component of all is that HDV only exists in humans. Here, we describe a novel deltavirus-like agent identified in wild birds. Although this agent is genetically divergent, it exhibits important similarities to HDV, such as the presence of ribosymes and self-complementarity. The discovery of an avian HDV-like agent challenges our understanding of both the origin and the co-evolutionary relationships of subviral agents with helper viruses.