The Zika virus (ZIKV) outbreak in 2016 in South America with specific pathogenic outcomes highlighted the need for new antiviral substances with broad-spectrum activities to react quickly to unexpected outbreaks of emerging viral pathogens. Very recently, the natural compound silvestrol isolated from the plant Aglaia foveolata was found to have very potent antiviral effects against the (−)-strand RNA-virus Ebola virus as well as against Corona- and Picornaviruses with a (+)-strand RNA-genome. This antiviral activity is based on the impaired translation of viral RNA by the inhibition of the DEAD-box RNA helicase eukaryotic initiation factor-4A (eIF4A) which is required to unwind structured 5´-untranslated regions (5′-UTRs) of several proto-oncogenes and thereby facilitate their translation. Zika virus is a flavivirus with a positive-stranded RNA-genome harboring a 5′-capped UTR with distinct secondary structure elements. Therefore, we investigated the effects of silvestrol on ZIKV replication in A549 cells and primary human hepatocytes. Two different ZIKV strains were used. In both infected A549 cells and primary human hepatocytes, silvestrol has the potential to exert a significant inhibition of ZIKV replication for both analyzed strains, even though the ancestor strain from Uganda is less sensitive to silvestrol. Our data might contribute to identify host factors involved in the control of ZIKV infection and help to develop antiviral concepts that can be used to treat a variety of viral infections without the risk of resistances because a host protein is targeted.

Zika virus (ZIKV) is a highly transmissive virus that belongs to the Flaviviridae family, which comprises several other pathogens that threaten human health. This re-emerging virus gained attention during the outbreak in Brazil in 2016, where a considerable number of microcephaly cases in newborns was associated with ZIKV infection during pregnancy. Lacking a preventive vaccine or antiviral drugs, efforts have been made to better understand the viral life cycle. In light of this, the relevance of the endosomal–lysosomal compartment for the ZIKV life cycle was investigated. A549 and SH-SY5Y cells were infected with either the African strain (associated with mild symptoms) or the French Polynesia strain (associated with neurological complications). For both strains, the V-ATPase inhibitor, bafilomycin A1, efficiently inhibited ZIKV entry and prevented the spread of the infection by interfering with viral maturation. Additionally, affecting cholesterol metabolism and transport with the drug U18666A, which inactivates late endosomes and lysosomes, impairs the viral life cycle. The data presented show a clear antiviral effect of two compounds that target the same compartments in different ways. This highlights the relevance of the endosomal–lysosomal compartment for the viral life cycle that should be considered as a target for antivirals.

Hepatitis D virus (HDV) is a defective RNA virus with a negative-strand RNA genome encompassing less than 1700 nucleotides. The HDV genome encodes only for one protein, the hepatitis delta antigen (HDAg), which exists in two forms acting as nucleoproteins. HDV depends on the envelope proteins of the hepatitis B virus as a helper virus for packaging its ribonucleoprotein complex (RNP). HDV is considered the causative agent for the most severe form of viral hepatitis leading to liver fibrosis/cirrhosis and hepatocellular carcinoma. Many steps of the life cycle of HDV are still enigmatic. This review gives an overview of the complete life cycle of HDV and identifies gaps in knowledge. The focus is on the description of cellular factors being involved in the life cycle of HDV and the deregulation of cellular pathways by HDV with respect to their relevance for viral replication, morphogenesis and HDV-associated pathogenesis. Moreover, recent progress in antiviral strategies targeting cellular structures is summarized in this article.

The N-terminus of the hepatitis B virus (HBV) large surface protein (LHB) differs with respect to genotypes. Compared to the amino terminus of genotype (Gt)D, in GtA, GtB and GtC, an additional identical 11 amino acids (aa) are found, while GtE and GtG share another similar 10 aa. Variants of GtB and GtC affecting this N-terminal part are associated with hepatoma formation. Deletion of these amino-terminal 11 aa in GtA reduces the amount of LHBs and changes subcellular accumulation (GtA-like pattern) to a dispersed distribution (GtD-like pattern). Vice versa, the fusion of the GtA-derived N-terminal 11 aa to GtD causes a GtA-like phenotype. However, insertion of the corresponding GtE-derived 10 aa to GtD has no effect. Deletion of these 11aa decreases filament size while neither the number of released viral genomes nor virion size and infectivity are affected. A negative regulatory element (aa 2–8) and a dominant positive regulatory element (aa 9–11) affecting the amount of LHBs were identified. The fusion of this motif to eGFP revealed that the effect on protein amount and subcellular distribution is not restricted to LHBs. These data identify a novel region in the N-terminus of LHBs affecting the amount and subcellular distribution of LHBs and identify release-promoting and -inhibiting aa residues within this motive.

Background & Aims: HBV genotype G (HBV/G) is mainly found in co‐infections with other HBV genotypes and was identified as an independent risk factor for liver fibrosis. This study aimed to analyse the prevalence of HBV/G co‐infections in healthy European HBV carriers and to characterize the crosstalk of HBV/G with other genotypes.Methods: A total of 560 European HBV carriers were tested via HBV/G‐specific PCR for HBV/G co‐infections. Quasispecies distribution was analysed via deep sequencing, and the clinical phenotype was characterized regarding qHBsAg‐/HBV‐DNA levels and frequent mutations. Replicative capacity and expression of HBsAg/core was studied in hepatoma cells co‐expressing HBV/G with either HBV/A, HBV/D or HBV/E using bicistronic vectors.Results: Although no HBV/G co‐infection was found by routine genotyping PCR, HBV/G was detected by specific PCR in 4%‐8% of patients infected with either HBV/A or HBV/E but only infrequently in other genotypes. In contrast to HBV/E, HBV/G was found as the quasispecies major variant in co‐infections with HBV/A. No differences in the clinical phenotype were observed for HBV/G co‐infections. In vitro RNA and DNA levels were comparable among all genotypes, but expression and release of HBsAg was reduced in co‐expression of HBV/G with HBV/E. In co‐expression with HBV/A and HBV/E expression of HBV/G‐specific core was enhanced while core expression from the corresponding genotype was markedly diminished.Conclusions: HBV/G co‐infections are common in European inactive carriers with HBV/A and HBV/E infection, but sufficient detection depends strongly on the assay. HBV/G regulated core expression might play a critical role for survival of HBV/G in co‐infections.