Abstract
Hepatitis delta virus (HDV) is a defective human virus that lacks the ability to produce its own envelope proteins and is thus dependent on the presence of a helper virus, which provides its surface proteins to produce infectious particles. Hepatitis B virus (HBV) was so far thought to be the only helper virus described to be associated with HDV. However, recent studies showed that divergent HDV-like viruses could be detected in fishes, birds, amphibians, and invertebrates, without evidence of any HBV-like agent supporting infection. Another recent study demonstrated that HDV can be transmitted and propagated in experimental infections ex vivo and in vivo by different enveloped viruses unrelated to HBV, including hepatitis C virus (HCV) and flaviviruses such as Dengue and West Nile virus. All this new evidence, in addition to the identification of novel virus species within a large range of hosts in absence of HBV, suggests that deltaviruses may take advantage of a large spectrum of helper viruses and raises questions about HDV origins and evolution.
Highlights
Academic Editor: Stefan UrbanReceived: 5 May 2021Accepted: 16 June 2021Published: 23 June 2021Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Licensee MDPI, Basel, Switzerland.Hepatitis D virus (HDV) was discovered 40 years ago in the liver of individuals chronically infected with hepatitis B virus (HBV) [1], a liver-specific pathogen present in ca. 250 million people
This RNP is composed of a multimer of the Hepatitis delta virus (HDV)-encoded delta antigen (HDAg) [2] that is associated with one copy of a 1.7 kb long circular single strand HDV RNA exhibiting self-annealing properties [2]
HDV-like viruses have been associated with animals long before their first appearance in humans [36] and during their evolutionary history
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. HDV forms enveloped particles with an average diameter of 36 nm that consists of cell-derived lipid vesicles harboring HBV surface proteins coating an inner ribonucleoprotein (RNP) [1]. This RNP is composed of a multimer of the HDV-encoded delta antigen (HDAg) [2] that is associated with one copy of a 1.7 kb long circular single strand HDV RNA exhibiting self-annealing properties [2]. For cell egress of its RNPs, HDV relies on the assistance of the helper HBV for the provision of GPs and a budding mechanism Their envelopment subsequently allows targeting and entry of HDV particles to human hepatocytes via mechanisms that depend on the same host factors that govern the early entry events of HBV itself.
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