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At least 19 recordsLinked to original sources
PubMed1975

Reactions of purified hemagglutinating antigens of flaviviruses with 19S and 7S antibodies.

The rapidly sedimenting hemagglutinin (RHA) representing the purified virion and the slower-sedimenting hemagglutinin (SHA) of several flaviviruses were separated and used in hemagglutination inhibition tests with the 19S (immunoglobulin M) and 7S (immunoglobulin G) immunoglobulin fractions of rabbit antisera, prepared against purified viral antigens or against crude virus pools. The antibody specificity in tests with RHA was identical to the specificity in those employing SHA. 7S antibody cross-reacted broadly with all flavivirus antigens, whereas 19S antibodies were relatively specific in cross-reactions among flaviviruses (RHA or SHA). SHA was consistently inhibited by antibody to a greater extent than RHA. Anti-envelope protein, anti-RHA antibodies and anti-SHA antibodies were unable to discriminate between RHA and SHA. It was concluded that the relative amounts of RHA or SHA in crude hemagglutinin preparations have no influence on the result of hemagglutination inhibition tests with flaviviruses.

Animals↗
PubMed1977

Antigenic characterization of flavivirus structural proteins separated by isoelectric focusing.

Isoelectrofocusing of nonionic-detergent-disrupted flaviviruses separated the envelope glycoprotein of 53,000 to 58,000 daltons and the nucleocapsid protein of 14,000 daltons. The envelope protein and nucleocapsid protein were isolated at isoelectric points of pI 7.8 and 10.3, respectively. The antigenic determinants of St. Louis encephalitis, Japanese encephalitis, and dengue virus envelope and nucleocapsid proteins were examined by solid-phase competition radioimmunoassay. By the appropriate selection of antiserum and competing proteins, it was possible to distinguish type-specific, complex-reactive and flavivirus group-reactive antigenic determinants. The envelope glycoproteins of St. Louis encephalitis, Japanese encephalitis, and dengue viruses were found to contain each of these three classes of antigenic determinants. Most of the determinants on the envelope protein were type specific, some were complex reactive, and a small fraction were flavivirus group reactive. The nucleocapsid protein contained only flavivirus group-reactive antigenic determinants.

Cell Line↗
PubMed1979

Antibody-mediated enhancement of Flavivirus replication in macrophage-like cell lines.

Interactions between animal viruses and antiviral antisera may exceptionally result in an apparent increase in viral infectivity. Halstead and coworkers demonstrated enhanced replication of dengue virus (a Flavivirus, family Togaviridae) in human or simian peripheral blood leucocytes carrying Fc receptors at subneutralising concentrations of antidengue antibody. We have used three continuous cell lines which express macrophage markers to explore the mechanism of this phenomenon. Dengue virus failed to replicate in these cells, but West Nile virus, another Flavivirus, replicated in all three, and we were able to demonstrate reproducibly 50--100-fold enhancement of virus yields in the presence of Flavivirus antisera, the effect also being directly demonstrable in P388D1 cells by increased numbers of virus-induced plaques. The phenomenon of antibody-dependent enhancement of viral replication is not unique to dengue virus, and may have far wider relevance in other viral infections.

Animals↗
PubMed2024

Cryo-electron tomography reveals coupled flavivirus replication, budding and maturation.

Flaviviruses replicate their genomes in replication organelles (ROs) formed as bud-like invaginations on the endoplasmic reticulum (ER) membrane, which also functions as the site for virion assembly. While this localization is well established, it is not known to what extent viral membrane remodeling, genome replication, virion assembly, and maturation are coordinated. Here, we imaged tick-borne flavivirus replication in human cells using cryo-electron tomography. We find that the RO membrane bud is shaped by a combination of a curvature-establishing coat and the pressure from intraluminal template RNA. A protein complex at the RO base extends to an adjacent membrane, where immature virions bud. Naturally occurring furin site variants determine whether virions mature in the immediate vicinity of ROs. We further visualize replication in mouse brain tissue by cryo-electron tomography. Taken together, these findings reveal a close spatial coupling of flavivirus genome replication, budding, and maturation.

Journal Article↗
PubMed2022

Flavivirus-Host Interaction Landscape Visualized through Genome-Wide CRISPR Screens.

Flaviviruses comprise several important human pathogens which cause significant morbidity and mortality worldwide. Like any other virus, they are obligate intracellular parasites. Therefore, studying the host cellular factors that promote or restrict their replication and pathogenesis becomes vital. Since inhibiting the host dependency factors or activating the host restriction factors can suppress the viral replication and propagation in the cell, identifying them reveals potential targets for antiviral therapeutics. Clustered regularly interspaced short palindromic repeats (CRISPR) technology has provided an effective means of producing customizable genetic modifications and performing forward genetic screens in a broad spectrum of cell types and organisms. The ease, rapidity, and high reproducibility of CRISPR technology have made it an excellent tool for carrying out genome-wide screens to identify and characterize viral host dependency factors systematically. Here, we review the insights from various Genome-wide CRISPR screens that have advanced our understanding of Flavivirus-Host interactions.

Humans↗
PubMed1977

Heterogeneity among flavivirus proteins separated in slab gels.

35S-methionine-labeled proteins specified in Vero cells by flaviviruses were analysed by SDS-phosphate electrophoresis in polyacrylamide slab gels. The clarity of the profile produced by Kunjin virus permitted designation of the nonstructural proteins, and confirmed the identity of NV21/2; the profile included a protein previously designated V2 (core protein) but now named NV11/2 because it migrates perceptibly faster than V2. Despite a varying background of labeled host proteins, identifiable profiles were obtained for 11 of 12 flaviviruses. The large non-structural proteins NV5 and NV4 migrated at apparently the same rates for all viruses. Profiles of the remaining proteins displayed varying amounts of heterogeneity, notably in the migration of the envelope protein V3 which showed no evidence of subgroup specificity.

Arboviruses↗
PubMed1977

The isolation of Saumarez Reef virus, a new flavivirus, from bird ticks Ornithodoros capensis and Ixodes eudyptidis in Australia.

Strains of a new flavivirus, for which the name Saumarez Reef Virus is proposed, were isolated from seabird ticks collected from four localities. Two strains were isolated from ticks of the species Ornithodoros capensis Neumann 1901 collected from the nests of Sooty Terns, Sterna fuscata Linnaeus 1766 on coral cays off the east coast of Queensland, Australia. The other three strains were isolated from ticks of the species Ixodes eudyptidis Maskell 1885 taken from two dead Silver Gulls Larus novaehollandiae Stephens 1826 in northern Tasmania. The new virus was compared serologically with 50 other flaviviruses at the Yale Arbovirus Research Unit and was found to be most closely related to Tyuleniy virus.

Animals↗
PubMedDate not supplied

Investigations on the presence of antibodies to alphaviruses, flaviviruses, Bunyavirus and Kemerovo virus in humans and some domestic animals.

The presence of antibodies to some alphaviruses, flaviviruses, bunyaviruses and orbiviruses was studied in the sera from humans and domestic animals of biotopes "C" and "T" in the south-east of Romania. Specific antibodies were found in humans to 3 alphaviruses (eastern equine encephalitis, western equine encephalitis and Sindbis), in a very low proportion, and to 3 flaviviruses (tickborne encephalitis, West Nile and Ntaya), at a much higher percentage. Very low percentages of antibodies to Bunyavirus and Kemerovo virus were also detected. The proportion of antibodies to flaviruses (tick-borne encephalitis, West Nile and Ntaya) detected in domestic animals (sheep, cattle and swine) is much lower than that found in humans of the same biotope ("T").

Animals↗
PubMed1976

"Karshi" virus, a new flavivirus (Togaviridae) isolated from Ornithodoros papillipes (Birula, 1895) ticks in Uzbek S.S.R.

Three identical strains of an arbovirus were isolated from 475 Ornithodoros papillipes ticks collected in June, 1972, in burrows of the great gerbil (Rhombomys opimus Licht., 1882) in the environs of Beshkent, Karshinsk steppe, Uzbek S.S.R. The isolate was found to range among flaviviruses. Complement-fixation, agar diffusion precipitation and neutralization tests is tissue culture and mice indicated a one-way antigenic relationship between the isolate and West Nile virus. However, the pattern of differences between them made it possible to consider the isolated agent as a new virus, "Karshi" virus. The results of electron microscopic studies of this virus are presented.

Animals↗
PubMed1976

Genetic resistance to lethal flavivirus encephalitis. I. Infection of congenic mice with Banzi virus.

Adult C3H/RV mice were highly resistant and adult C3H/He mice were highly susceptible to lethal encephalitis after intraperitoneal inoculation of Banzi virus (flavivirus), but the infectivity of the virus was the same for both strains of mice. Yields of virus were similar from lymphoid tissues of C3H/He and C3H/RV adult mice, but titers of virus in the brain were significantly lower in C3H/RV mice. Lesions of encephalitis developed in both strains but remained mild and self-limiting in C3H/RV mice, whereas widespread necrosis occurred in the brains of C3H/He mice. Resistance to lethal infection after intraperitoneal inoculation developed postnatally in C3H/RV mice and did not reach significant levels until mice were at least four weeks old. Mortality rates among C3H/RV and C3H/He mice were comparable after intracerebral inoculation of virus. Yields of virus, brain lesions, and immunofluorescent staining patterns for viral antigen were similar in intracerebrally inoculated C3H/He and C3H/RV mice. Results indicate that tissues of resistant and susceptible mice in vivo can support replication of Banzi virus about equally well. Thus, genetic resistance to lethal infection with Banzi virus in these strains of mice does not seem to be solely dependent on resistance of tissues to viral replication.

Animals↗
PubMed1979

T cell-mediated cytotoxicity for L 929 fibroblasts infected with Banzi virus (flavivirus).

During infection with Banzi virus, splenic thymus-derived cells of C3H/RV mice developed immunologically specific cytotoxicity for Banzi virus-infected, C3H-derived L 929 fibroblasts. Cytotoxic activity was detected by six days after viral inoculation, was maximal by eight days, and decreased to background levels by 16 days. There was no consistently significant difference in Banzi virus-specific cytotoxicity of spleen cells from C3H/RV and C3H/He mice, which are genetically resistant and susceptible, respectively, to the lethal flaviviral encephalitis. Therefore, the ability of the host to develop killer cells did not, in itself, lead to protection from lethal infection. These experiments are, to our knowledge, the first demonstration of cell-mediated cytotoxicity to a flavivirus.

Animals↗
PubMed1975

Influence of certain immunodepressants on experimental flavivirus and enterovirus infections in mice.

The effects of cyclophosphamide and 1,3-(piperidinomethyl)-5-phenyl-5-ethylbarbituric acid on certain flavi- and enterovirus infections in mice were studied. Differential enhancement of mortality rates after extraneural and, less markedly, intracerebral virus inoculation was noted. While depression of humoral and/or cell-mediated immunity is considered to be responsible for the effects observed in flavivirus infections, impaired function of the reticuloendothelial system seems to contribute mainly to the potentiation of Mengo virus infection by the immunodepressants used.

Animals↗
PubMed1976

The opposite temperature-sensitivity character (ts) in two attenuated flaviviruses, used for human immunization: 17D yellow fever and E5"14" (Langat) viruses. A reappraisal of thoughts.

For the reproduction of the man-attenuated E5"14" clone of the Langat virus (tick-borne encephalitis complex) in pig kidney epithelial cells, the temperature of 39 degrees C was shown as restrictive, whereas it was permissive for the 17D strain of yellow fever virus and three virulent strains of tick-borne encephalitis (western subtype) virus. The temperature of 36 degrees C permitted the reproduction of all viruses studied. The implication of genetic marker studies in the assessment of human neuropathogenicity of flaviviruses is discussed.

Arboviruses↗
PubMed1977

Interspecies interactions of arboviruses. II. Participation of the genomes of two flaviviruses, West Nile and Japanese encephalitis, in formation of a virus clone with dual antigenic determinants.

A peculiar clone, 41/WN+JE+, possessing antigenic determinants of a flaviviruses, West Nile (WN) and Japanese encphalitis (JE), is described. The antigenic duality of this clone exceeded the cross reactions between WN and JE viruses; either antiserum neutralized 104--105 PFU/ml of the virus. The property of antigenic duality was inherited in over 340 virus generations and retained upon propagation in selective cell systems and after recloning. The progeny of infectious RNA consisted of 3 types of virus particle: antigenetically distinct WN and JE viruses and particles retaining dual antigenic determinants WN+JE+. The nature of clone 41/WN+JE+ (a stable heterozygote accompanied by phenotypic mixing) and its origin due to inadvertent contamination of attenuated WN virus with JE virus is discussed.

Animals↗
PubMed1976

[Transovarian transmission of a Flavivirus, the Koutango virus, in Aedes aegypti L].

The Koutango virus Dak An D 5443 isolated from rodents of the genus Tatera belongs to the genus Flavivirus of the faily Togaviridae. This virus is very similar to the yellowfever, virus. It is experimentally transmitted from young Mouse to young Mouse by Aedes aegypti. The following observations show on one hand that this virus is found in the eggs of infected A. aegypti and on the other that the females from these eggs transmit the virus to the young Mouse by biting them.

Aedes↗
PubMed2024

Identification and epidemiological study of an uncultured flavivirus from ticks using viral metagenomics and pseudoinfectious viral particles.

During their blood-feeding process, ticks are known to transmit various viruses to vertebrates, including humans. Recent viral metagenomic analyses using next-generation sequencing (NGS) have revealed that blood-feeding arthropods like ticks harbor a large diversity of viruses. However, many of these viruses have not been isolated or cultured, and their basic characteristics remain unknown. This study aimed to present the identification of a difficult-to-culture virus in ticks using NGS and to understand its epidemic dynamics using molecular biology techniques. During routine tick-borne virus surveillance in Japan, an unknown flaviviral sequence was detected via virome analysis of host-questing ticks. Similar viral sequences have been detected in the sera of sika deer and wild boars in Japan, and this virus was tentatively named the Saruyama virus (SAYAV). Because SAYAV did not propagate in any cultured cells tested, single-round infectious virus particles (SRIP) were generated based on its structural protein gene sequence utilizing a yellow fever virus-based replicon system to understand its nationwide endemic status. Seroepidemiological studies using SRIP as antigens have demonstrated the presence of neutralizing antibodies against SAYAV in sika deer and wild boar captured at several locations in Japan, suggesting that SAYAV is endemic throughout Japan. Phylogenetic analyses have revealed that SAYAV forms a sister clade with the Orthoflavivirus genus, which includes important mosquito- and tick-borne pathogenic viruses. This shows that SAYAV evolved into a lineage independent of the known orthoflaviviruses. This study demonstrates a unique approach for understanding the epidemiology of uncultured viruses by combining viral metagenomics and pseudoinfectious viral particles.

Animals↗
PubMed2026

Field-isolate recombinant tick-borne encephalitis viruses define reporter-stability guidelines for antiviral testing in flaviviruses.

As arthropod-borne viruses continue to threaten populations globally, there is a pressing need for experimental systems that enable rapid antiviral discovery. Reverse-genetics platforms producing recombinant reporter orthoflaviviruses have been developed to address this gap. Here, we present two new recombinant tick-borne encephalitis viruses (TBEVrec) generated on a European-subtype Haselmühl Tiho1 isolate backbone. A reporter gene, either eGFP or Nluc, was inserted in the capsid-coding region of the genome downstream of the capsid RNA regulatory signal and separated from the complete viral polyprotein by a 2A self-cleaving peptide. TBEVrec was better rescued using the circular polymerase extension reaction (CPER) than with the infectious subgenomic amplicon (ISA) method. TBEVrec replicated efficiently in relevant human cell lines, with comparable replication to wild-type TBEV in a neuronal cell line and moderately reduced titers and RNA levels in immune-derived cell lines. Using either eGFP or Nluc, we illustrate how TBEVrec enabled high-content RNAi screening, highlighting Nucleolin and PRKD1 as potential TBEV host factors, and drug testing on a benchtop plate reader. Nanopore sequencing of the eGFP insert revealed that the reporter is excised without affecting flanking regions. Comparative analysis of eGFP and Nluc further shows that this instability is time- and cell type-dependent, and that Nluc is comparatively more stable. From these observations, we outline safeguards and design principles that are broadly applicable both to the rescue of existing constructs and to the design of future recombinant reporter virus platforms.

CPER↗