HDV

HDV Full Name

Hepatitis D Virus

HDV Introduction

In the last century, researchers studying the nuclei of hepatocytes from HBsAg-positive patients with unusually severe liver pathological manifestations discovered a new antigen system, initially named the "delta antigen" (HDAg). Subsequent studies confirmed that this antigen was part of a novel pathogen—an RNA virus whose transmission and pathogenicity rely entirely on the assistance of Hepatitis B Virus (HBV). It was thus named Hepatitis D Virus. In viral taxonomy, HDV holds an extremely unique position. It does not belong to any known virus family and is independently classified within the family Deltaviridae (the delta virus family), serving as the sole member of the genus Deltavirus. This distinct taxonomic status highlights its evolutionary isolation.

Figure 1. Hepatitis B virus (HBV) shares its small, medium and large hepatitis B surface antigens (HBsAg) with hepatitis D virus (HDV), acting as a helper virus of HDV. (Source: Sagnelli C, et al. 2021)

The most notable feature of HDV is its nature as a "satellite virus." It lacks the gene encoding its own envelope protein and therefore cannot complete its life cycle independently. To form infectious, complete viral particles and facilitate transmission from one hepatocyte to another, HDV must "borrow" the surface antigen (HBsAg) produced by its helper virus, HBV, as its outer coat. This absolute dependency means that without coexisting HBV infection, HDV infection cannot be established or sustained. HDV particles closely resemble HBV virions (Dane particles) in morphology, as they share the same outer envelope—a lipid bilayer composed of large, medium, and small HBsAg proteins. Within this envelope lies the viral core, a ribonucleoprotein complex (RNP), consisting of the HDV genomic RNA tightly bound to its encoded Hepatitis D Antigen (HDAg). The HDV genome is a single-stranded, negative-sense, circular RNA approximately 1.7 kilobases (kb) in length. This tiny RNA molecule possesses an intriguing structural feature: due to extensive internal base-pairing (accounting for about 70% of its sequence), the entire genome folds into a highly stable, unbranched "rod-like structure." This conformation not only provides exceptional stability, resisting degradation by host cell nucleases, but also shows remarkable similarity in shape and certain replication mechanisms to plant viroids, sparking widespread speculation about the origin and evolution of HDV.

The functions of S-HDAg and L-HDAg are mutually antagonistic, forming a precise regulatory switch. In the early stages of infection, S-HDAg predominates, primarily promoting and maintaining efficient replication of the viral genome. As infection progresses, RNA editing is activated, increasing the production of L-HDAg. L-HDAg inhibits viral genome replication, while its C-terminal extension undergoes prenylation—a modification critical for viral assembly. This "tail" acts as a key signal, enabling interaction with HBsAg on the endoplasmic reticulum membrane. It mediates the packaging of the HDV genomic RNA and HDAg-containing RNP core into the envelope, facilitating virion assembly and release. The shift from S-HDAg to L-HDAg marks the transition in the HDV life cycle from the "replication phase" to the "assembly and release phase," representing a tightly controlled and highly efficient process.

Alternate Names for HDV

HDV; Hepatitis D Virus; Hepatitis D; Unassigned; Deltavirus

• 1. Tseligka ED, et al. HDV Pathogenesis: Unravelling Ariadne's Thread. Viruses. 2021 Apr 28;13(5):778.
  2. Sagnelli C, et al. HBV/HDV Co-Infection: Epidemiological and Clinical Changes, Recent Knowledge and Future Challenges. Life (Basel). 2021 Feb 22;11(2):169.