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Concept: Flavivirus


Although the outcome of flavivirus infection can vary from asymptomatic to lethal, environmental factors modulating disease severity are poorly defined. Here, we observed increased susceptibility of mice to severe West Nile (WNV), Dengue, and Zika virus infections after treatment with oral antibiotics (Abx) that depleted the gut microbiota. Abx treatment impaired the development of optimal T cell responses, with decreased levels of WNV-specific CD8+T cells associated with increased infection and immunopathology. Abx treatments that resulted in enhanced WNV susceptibility generated changes in the overall structure of the gut bacterial community and in the abundance of specific bacterial taxa. As little as 3 days of treatment with ampicillin was sufficient to alter host immunity and WNV outcome. Our results identify oral Abx therapy as a potential environmental determinant of systemic viral disease, and they raise the possibility that perturbation of the gut microbiota may have deleterious consequences for subsequent flavivirus infections.

Concepts: Immune system, Bacteria, Virus, Antibiotic, Penicillin, West Nile virus, Flavivirus, Flaviviridae


BACKGROUND: The genus Flavivirus includes several pathogenic agents that cause severe illness in humans. Re-emergence of West Nile virus in Europe and continuous spread of certain flaviviruses such as dengue, yellow fever and Japanese encephalitis viruses represent a global danger to public health. Therefore, a rapid and accurate molecular method is required for diagnostics and epidemiological surveillance of flaviviruses. METHODS: A Pan-Flavi quantitative RT-PCR assay using a Locked-Nucleic Acid probe targeting the flavivirus NS5 gene was developed and optimized to detect a wide range of flaviviruses simultaneously. The specificity and sensitivity of the Pan-Flavi assay were tested using RNA of different flaviviruses and non-flaviviruses. Furthermore, the assay was compared directly to flavivirus species-specific assays for the ability to detect flaviviruses sensitively. RESULTS: Two degenerate primers and one Locked-Nucleic Acids probe were designed to amplify most of the flaviviruses. To increase the specificity and fluorescence signal of the Pan-Flavi assay for detection of yellow fever virus and dengue virus 4, additional primers and probes were included. Viral RNA of thirty different flaviviruses was detected, verifying the broad range specificity. The testing of this assay was successful, using standard plasmid and RNA dilutions of yellow fever virus vaccine strain, dengue virus 1 and tick-borne encephalitis virus, with a sensitivity limit of 10–100 genome copies/reaction. Also comparatively good results were achieved for detecting different flaviviruses by the Pan-Flavi assay when compared to the flavivirus species-specific assays. CONCLUSION: The assay is rapid, broad-range flavivirus-specific and highly sensitive making it a valuable tool for rapid detection of flaviviruses in livestock samples, epidemiological studies or as useful complement to single flavivirus-specific assays for clinical diagnosis.

Concepts: Malaria, Ribavirin, Viral diseases, Encephalitis, West Nile virus, Flavivirus, Flaviviridae, Flaviviruses


The outbreak of West Nile virus (WNV) in 1999 in the USA, and its continued spread throughout the Americas, parts of Europe, the Middle East and Africa, underscored the need for WNV antiviral development. Here, we review the current status of WNV drug discovery. A number of approaches have been used to search for inhibitors of WNV, including viral infection-based screening, enzyme-based screening, structure-based virtual screening, structure-based rationale design, and antibody-based therapy. These efforts have yielded inhibitors of viral or cellular factors that are critical for viral replication. For small molecule inhibitors, no promising preclinical candidate has been developed; most of the inhibitors could not even be advanced to the stage of hit-to-lead optimization due to their poor drug-like properties. However, several inhibitors developed for related members of the family Flaviviridae, such as dengue virus and hepatitis C virus, exhibited cross-inhibition of WNV, suggesting the possibility to re-purpose these antivirals for WNV treatment. Most promisingly, therapeutic antibodies have shown excellent efficacy in mouse model; one of such antibodies has been advanced into clinical trial. The knowledge accumulated during the past fifteen years has provided better rationale for the ongoing WNV and other flavivirus antiviral development.

Concepts: Microbiology, Middle East, Ribavirin, Dengue fever, West Nile virus, Flavivirus, Flaviviridae, Flaviviruses


Glioblastoma is a highly lethal brain cancer that frequently recurs in proximity to the original resection cavity. We explored the use of oncolytic virus therapy against glioblastoma with Zika virus (ZIKV), a flavivirus that induces cell death and differentiation of neural precursor cells in the developing fetus. ZIKV preferentially infected and killed glioblastoma stem cells (GSCs) relative to differentiated tumor progeny or normal neuronal cells. The effects against GSCs were not a general property of neurotropic flaviviruses, as West Nile virus indiscriminately killed both tumor and normal neural cells. ZIKV potently depleted patient-derived GSCs grown in culture and in organoids. Moreover, mice with glioblastoma survived substantially longer and at greater rates when the tumor was inoculated with a mouse-adapted strain of ZIKV. Our results suggest that ZIKV is an oncolytic virus that can preferentially target GSCs; thus, genetically modified strains that further optimize safety could have therapeutic efficacy for adult glioblastoma patients.

Concepts: DNA, Neuron, Oncology, Microbiology, Brain tumor, Viruses, West Nile virus, Flavivirus


The recent rapid spread of Zika virus and its unexpected linkage to birth defects and an autoimmune-neurological syndrome has generated worldwide concern. Zika virus is a flavivirus like dengue, yellow fever and West Nile viruses. We present the 3.8Å resolution structure of mature Zika virus determined by cryo-electron microscopy. The structure of Zika virus is similar to other known flavivirus structures except for the ~10 amino acids that surround the Asn154 glycosylation site found in each of the 180 envelope glycoproteins that make up the icosahedral shell. The carbohydrate moiety associated with this residue, recognizable in the cryo-EM electron density, may function as an attachment site of the virus to host cells. This region varies not only among Zika virus strains but also in other flaviviruses and suggests that changes in this region influence virus transmission and disease.

Concepts: Protein, Virus, Ribavirin, Viruses, West Nile virus, Flavivirus, Flaviviridae, Flaviviruses


Although Zika virus (ZIKV) infection in pregnant women can cause placental damage, intrauterine growth restriction, microcephaly, and fetal demise, these disease manifestations only became apparent in the context of a large epidemic in the Americas. We hypothesized that ZIKV is not unique among arboviruses in its ability to cause congenital infection. To evaluate this, we tested the capacity of four emerging arboviruses [West Nile virus (WNV), Powassan virus (POWV), chikungunya virus (CHIKV), and Mayaro virus (MAYV)] from related (flavivirus) and unrelated (alphavirus) genera to infect the placenta and fetus in immunocompetent, wild-type mice. Although all four viruses caused placental infection, only infection with the neurotropic flaviviruses (WNV and POWV) resulted in fetal demise. WNV and POWV also replicated efficiently in second-trimester human maternal (decidua) and fetal (chorionic villi and fetal membrane) explants, whereas CHIKV and MAYV replicated less efficiently. In mice, RNA in situ hybridization and histopathological analysis revealed that WNV infected the placenta and fetal central nervous system, causing injury to the developing brain. In comparison, CHIKV and MAYV did not cause substantive placental or fetal damage despite evidence of vertical transmission. On the basis of the susceptibility of human maternal and fetal tissue explants and pathogenesis experiments in immunocompetent mice, other emerging neurotropic flaviviruses may share with ZIKV the capacity for transplacental transmission, as well as subsequent infection and injury to the developing fetus.

Concepts: Pregnancy, Fetus, Virus, Infection, Placenta, Flavivirus, Flaviviruses, DEET


The mosquito-borne flaviviruses include important human pathogens such as dengue, Zika, West Nile, and yellow fever viruses, which pose a serious threat for global health. Recent genetic screens identified endoplasmic reticulum (ER)-membrane multiprotein complexes, including the oligosaccharyltransferase (OST) complex, as critical flavivirus host factors. Here, we show that a chemical modulator of the OST complex termed NGI-1 has promising antiviral activity against flavivirus infections. We demonstrate that NGI-1 blocks viral RNA replication and that antiviral activity does not depend on inhibition of the N-glycosylation function of the OST. Viral mutants adapted to replicate in cells deficient of the OST complex showed resistance to NGI-1 treatment, reinforcing the on-target activity of NGI-1. Lastly, we show that NGI-1 also has strong antiviral activity in primary and disease-relevant cell types. This study provides an example for advancing from the identification of genetic determinants of infection to a host-directed antiviral compound with broad activity against flaviviruses.

Concepts: Protein, Gene, Genetics, Bacteria, Virus, Flavivirus, Flaviviridae, Flaviviruses


Zika virus (ZIKV) is spreading rapidly into regions around the world where other flaviviruses, such as dengue (DENV) and West Nile virus (WNV) are endemic. Antibody-dependent enhancement (ADE) has been implicated in more severe forms of flavivirus disease, but whether this also applies to ZIKV infection is unclear. Using convalescent plasma from DENV and WNV infected individuals, we found substantial enhancement of ZIKV infection in vitro that was mediated through IgG engagement of Fcγ receptors. Administration of DENV or WNV convalescent plasma into ZIKV-susceptible mice resulted in increased morbidity and mortality, including fever, viremia, and viral loads in spinal cord and testes. ADE may explain the severe disease manifestations associated with recent ZIKV outbreaks and highlights the need to exert great caution when designing flavivirus vaccines.

Concepts: Immune system, Infection, Viruses, Dengue fever, West Nile virus, Flavivirus, Flaviviridae, Flaviviruses


West Nile virus (WNV), which is an emerging pathogenic flavivirus with increasing distribution worldwide, is the cause of major human and animal health concerns. The pre-membrane (prM) protein of WNV is cleaved during maturation by the furin protease into the structural protein M and a pr-segment. In this study we generated and characterized a monoclonal antibody (MAb) against the WNV prM protein. Western blot analysis showed that the MAb reacted with WNV prM specifically. Immunohistochemistry assays demonstrated that the MAb recognized native prM protein in transfected BHK-21 cells. Preliminary studies were performed to identify the epitope recognized by the MAb using a set of synthesized overlapping peptides spanning the whole length of the prM protein. The MAb reported here may provide a valuable tool for the further exploration of the biological properties and functions of the prM protein and may also be developed for potential clinical applications.

Concepts: Immune system, Antibody, Protein, Microbiology, Monoclonal antibodies, Western blot, West Nile virus, Flavivirus


Studies have demonstrated cross-reactivity of anti-dengue virus (DENV) antibodies in human sera against Zika virus (ZIKV), promoting increased ZIKV infection in vitro. However, the correlation between in vitro and in vivo findings is not well characterized. Thus, we evaluated the impact of heterotypic flavivirus immunity on ZIKV titers in biofluids of rhesus macaques. Animals previously infected (≥420 days) with DENV2, DENV4, or yellow fever virus were compared to flavivirus-naïve animals following infection with a Brazilian ZIKV strain. Sera from DENV-immune macaques demonstrated cross-reactivity with ZIKV by antibody-binding and neutralization assays prior to ZIKV infection, and promoted increased ZIKV infection in cell culture assays. Despite these findings, no significant differences between flavivirus-naïve and immune animals were observed in viral titers, neutralizing antibody levels, or immune cell kinetics following ZIKV infection. These results indicate that prior infection with heterologous flaviviruses neither conferred protection nor increased observed ZIKV titers in this non-human primate ZIKV infection model.

Concepts: Immune system, Antibody, Yellow fever, Immunity, Macaque, Primate, Rhesus Macaque, Flavivirus