Structural and functional similarities in bunyaviruses: Perspectives for pan-bunya antivirals.

The order of Bunyavirales includes numerous (re)emerging viruses that collectively have a major impact on human and animal health worldwide. There are no vaccines for human use or antiviral drugs available to prevent or treat infections with any of these viruses. The development of efficacious and safe drugs and vaccines is a pressing matter. Ideally, such antivirals possess pan-bunyavirus antiviral activity, allowing the containment of every bunya-related threat. The fact that many bunyaviruses need to be handled in laboratories with biosafety level 3 or 4, the great variety of species and the frequent emergence of novel species complicate such efforts. We here examined the potential druggable targets of bunyaviruses, together with the level of conservation of their biological functions, structure, and genetic similarity by means of heatmap analysis. In the light of this, we revised the available models and tools currently available, pointing out directions for antiviral drug discovery.

Characterization of five unclassified orthobunyaviruses (Bunyaviridae) from Africa and the Americas.

The Bunyaviridae family is made up of a diverse range of viruses, some of which cause disease and are a cause for concern in human and veterinary health. Here, we report the genomic and antigenic characterization of five previously uncharacterized bunyaviruses. Based on their ultrastructure, antigenic relationships and phylogenomic relationships, the five viruses are classified as members of the Orthobunyavirus genus. Three are viruses in the California encephalitis virus serogroup and are related to Trivittatus virus; the two others are most similar to the Mermet virus in the Simbu serogroup, and to the Tataguine virus, which is not currently assigned to a serogroup. Each of these five viruses was pathogenic to newborn mice, indicating their potential to cause illness in humans and other animals.

Genetic Characterization of Archived Bunyaviruses and their Potential for Emergence in Australia.

To better understand the diversity of bunyaviruses and their circulation in Australia, we sequenced 5 viruses (Gan Gan, Trubanaman, Kowanyama, Yacaaba, and Taggert) isolated and serologically identified 4 decades ago as members of the family Bunyaviridae. Gan Gan and Trubanaman viruses almost perfectly matched 2 recently isolated, purportedly novel viruses, Salt Ash and Murrumbidgee viruses, respectively. Kowanyama and Yacaaba viruses were identified as being related to members of a large clade containing pathogenic viruses. Taggert virus was confirmed as being a nairovirus; several viruses of this genus are pathogenic to humans. The genetic relationships and historical experimental infections in mice reveal the potential for these viruses to lead to disease emergence.

Cell culture and electron microscopy for identifying viruses in diseases of unknown cause.

During outbreaks of infectious diseases or in cases of severely ill patients, it is imperative to identify the causative agent. This report describes several events in which virus isolation and identification by electron microscopy were critical to initial recognition of the etiologic agent, which was further analyzed by additional laboratory diagnostic assays. Examples include severe acute respiratory syndrome coronavirus, and Nipah, lymphocytic choriomeningitis, West Nile, Cache Valley, and Heartland viruses. These cases illustrate the importance of the techniques of cell culture and electron microscopy in pathogen identification and recognition of emerging diseases.

Bunyavirus: structure and replication.

The Bunyaviridae family is comprised of a large number of negative-sense, single-stranded RNA viruses that infect animals, insects, and plants. The tripartite genome of bunyaviruses, encapsidated in the form of individual ribonucleoprotein complexes, encodes four structural proteins, the glycoproteins Gc and Gn, the nucleoprotein N, and the viral polymerase L. Some bunyaviruses also use an ambi-sense strategy to encode the nonstructural proteins NSs and NSm. While some bunyaviruses have a T = 12 icosahedral symmetry, others only have locally ordered capsids, or capsids with no detectable symmetry. Bunyaviruses enter cells through clathrin-mediated endocytosis or phagocytosis. In endosome, viral glycoproteins facilitate membrane fusion at acidic pH, thus allowing bunyaviruses to uncoat and deliver their genomic RNA into host cytoplasm. Bunyaviruses replicate in cytoplasm where the viral polymerase L catalyzes both transcription and replication of the viral genome. While transcription requires a cap primer for initiation and ends at specific termination signals before the 3' end of the template is reached, replication copies the entire template and does not depend on any primer for initiation. This review will discuss some of the most interesting aspects of bunyavirus replication, including L protein/N protein-mediated cap snatching, prime-and-realign for transcription and replication initiation, translation-coupled transcription, sequence/secondary structure-dependent transcription termination, ribonucleoprotein encapsidation, and N protein-mediated initiation of viral protein translation. Recent developments on the structure and functional characterization of the bunyavirus capsid and the RNA synthesis machineries (including both protein L and N) will also be discussed.

Viral diseases in commercially exploited crabs: a review.

Viruses and viral diseases of crabs were observed and investigated earlier than the first observation of viruses in shrimp. In fact, crabs were used as biological models to investigate crustacean virology at the beginning of shrimp aquaculture development. More than 30 viruses have been reported in crabs, including those related to the known virus families Reoviridae, Bunyaviridae, Roniviridae and a group of Bacilliform enveloped nuclear viruses. This review reports data on several important viral diseases of crabs, particularly those associated with pathology of organs and tissues of commercially and ecologically significant host species.

Molecular Characteristics of Jujube Yellow Mottle-Associated Virus Infecting Jujube (Ziziphus jujuba Mill.) Grown at Aksu in Xinjiang of China.

Chinese jujube (Ziziphus jujuba Mill.) is a native fruit crop in China. Leaf mottle and dapple fruit disease is prevalent in cultivated jujube plants grown at Aksu in Xinjiang Uygur Autonomous Region of China. Jujube yellow mottle-associated virus (JYMaV), a tentative member in the genus Emaravirus, was recently identified from mottle-diseased jujube plants grown in Liaoning Province in China, but its incidence and genetic diversity in China is unknown. In this study, the genome sequences of three JYMaV isolates from two jujube cultivars and one jujube variant were determined by high-throughput sequencing (HTS) for small RNA and rRNA-depleted RNA coupled with RT-PCR assays. Comparison of these sequences together with sequences of the viral RNA segments derived by primer set 3C/5H-based RT-PCR revealed that genetic diversity was present in the virus populations and high sequence variation occurred at the non-translational regions of each of the viral genomic segments. Field investigation confirmed the close association of the virus with leaf mottle symptoms of jujube plants. Furthermore, this study revealed that P5 encoded in the viral RNA5 displayed a nuclear localization feature differing from the plasmodesma (PD) subcellular localization of the virus movement protein (P4), and the two proteins could interact with each other in the BiFC assays. Our study provides a snapshot of JYMaV genetic diversity in its natural hosts.

Formation and intracellular transport of a heterodimeric viral spike protein complex.

We have analyzed the heterodimerization and intracellular transport from the ER to the Golgi complex (GC) of two membrane glycoproteins of a bunyavirus (Uukuniemi virus) that matures by a budding process in the GC. The glycoproteins G1 and G2, which form the viral spikes, are cotranslationally cleaved in the ER from a 110,000-D precursor. Newly synthesized G1 was transported to the GC and incorporated into virus particles about 30-45 min faster than newly synthesized G2. Analysis of the kinetics of intrachain disulfide bond formation showed that G1 acquired its mature form within 10 min, while completion of disulfide bond formation of G2 required a considerably longer time (up to 60 min). During the maturation process, G2 was transiently associated with the IgG heavy chain binding protein for a longer time than G1. Protein disulfide isomerase also coprecipitated with antibodies against G1 and G2. In virus particles, G1 and G2 were present exclusively as heterodimers. Immunoprecipitation with monoclonal antibodies showed that heterodimerization occurred rapidly, probably in the ER, between newly made G1 and mature, dimerization competent G2. Taken together, our results show that these two viral glycoproteins have different maturation kinetics in the ER. We conclude that the apparent different kinetics of ER to GC transport of G1 and G2 is due to the different rates by which these proteins fold and become competent to enter into heterodimeric complexes prior to exit from the ER.

Isolation of Tete serogroup bunyaviruses from Ceratopogonidae collected in Colorado.

Two viruses were isolated from ceratopogonid midges collected in northern Colorado. Electron microscopy indicated that both isolates were bunyavirus-like. Indirect fluorescent antibody and serum dilution-plaque reduction neutralization tests showed that these isolates were members of the Tete serogroup, most closely related antigenically to Tete and Batama viruses but distinguishable from both and from each other. We suggest the name Weldona virus for these isolates. Antibody in both waterfowl and passerine birds in northern Colorado indicates the enzootic presence of these viruses in northern Colorado and raises unanswered questions about the introduction and establishment of Tete serogroup viruses in the Americas.

A method for increasing the surface details of resin embedded viruses using Congo/Crimean haemorrhagic fever virus as a model.

The surface details of resin embedded viruses can be greatly enhanced by the use of uranyl acetate block staining. The virions are embedded in agar immediately after fixation and block stained with 3% uranyl acetate in methanol during dehydration. This technique allows those particles outside their host cells to show clearly the spikes normally seen only by the separate use of negative staining.

Isolation and characterization of Sedlec virus, a new bunyavirus from birds.

A pathogenic agent designated AV 172 was isolated from the blood of a Reed Warbler (Acrocephalus scirpaceus) out of 767 samples from birds belonging to 35 species and 14 families. The birds (largely wetland passerines) were captured in the reed-belt littoral of Nesyt fishpond in southern Moravia, Czechoslovakia, during the years 1984 to 1987. Virus AV 172 has been found to represent probably a new species (designated virus "Sedlec") of family Bunyaviridae. Sedlec virus is pathogenic to suckling and adult mice when inoculated intracerebrally (i.c.) but not intraperitoneally (i.p.) and its ether-sensitive spherical particles measures 90-100 nm.

Avalon virus, Sakhalin group (Nairovirus, Bunyaviridae) from the seabird tick Ixodes (Ceratixodes) uriae White 1852 in France.

Nine strains of Avalon virus were isolated from Ixodes uriae ticks collected in the Cape Sizun seabird reserve, Brittany, from 1979 to 1985, during a longitudinal study of consequences of tick-borne infections for kittiwakes (Rissa tridactyla). Avalon virus strains isolated in France proved difficult to study owing to the weak infectious titres they exhibited in suckling mice or cultured cells. However, some interesting data concerning the ecology of virus infection and the morphology of the virions were obtained and are discussed.

[Sakhalin antigenic group (Bunyaviridae family)]. / Antigennaia gruppa Sakhalin (semeistvo Bunyaviridae).

Serological study of viruses belonging to the Sakhalin group showed Paramushir virus isolated in the USSR and Avalon virus isolated in Canada to be identical in all the tests used. The data on the cultural properties of the Sakhalin group viruses, the virions buoyant densities in sucrose gradient, the data on thermal sensitivity and UV inactivation of the viruses, on their morphology and morphogenesis are presented.

[Virus--the causative agent of hemorrhagic fever with renal syndrome--a new representative of the family Bunyaviridae]. / Virus--vozbuditel' gemorragicheskoi likhoradki s pochechnym sindromom--novyi predstavitel' semeistva Bunyaviridae.

Physicochemical characteristics (sedimentation coefficient, buoyant density of particles, as well as ribonuclein of these particles) and morphology of the causative agent of hemorrhagic fever with renal syndrome were found to be similar to those of the other members of the Bunyaviridae family.

[Visualization of the Soldado virus by electron microscopy in the tissues of the vector tick Ornithodoros (Alectorobius) maritimus Vermeil and Marguet, 1967]. / Visualisation du virus soldado par la microscopie électronique dans les tissus de la tique vectrice Ornithodoros (Alectorobius) maritimus Vermeil et Marguet, 1967.

By means of transmission electron microscopy, it was possible to visualize typical viral particles of Soldado virus (Bunyaviridae, Nairovirus ) in the tissues of a naturally infected Ornithodoros ( Alectorobius ) maritimus tick.

Distinction between Bunyaviridae genera by surface structure and comparison with Hantaan virus using negative stain electron microscopy.

Ultrastructural studies of glutaraldehyde-fixed viruses of the Bunyaviridae were performed by negative-stain electron microscopy. The surface structure of viruses of each genus was compared with that of the other genera and with Hantaan virus, the prototype of a proposed new genus of Bunyaviridae. Viruses of each genus had a surface structure distinct for that genus. In addition, Hantaan virus had a surface structure composed of a grid-like pattern of morphologic subunits not previously described for animal viruses. Careful morphologic studies of suspected Bunyaviridae may be used in considering preliminary generic assignment. This study also supports the assignment of Hantaan-related viruses to a separate generic status within the Bunyaviridae.