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|Vesicular stomatitis Indiana virus (VSIV), the prototypical rhabdovirus|
The Rhabdoviridae are a family of viruses in the order Mononegavirales. Vertebrates (including mammals and humans), invertebrates, and plants serve as natural hosts. Currently, 18 genera are recognised. Diseases associated with viruses of this family include rabies encephalitis caused by rabies virus, and vesicular diseases and encephalitis flu-like symptoms in humans caused by vesiculoviruses. The name is derived from the Greek rhabdos, meaning rod, referring to the shape of the viral particles.
Rhabdovirions are enveloped, with bullet-shaped and bacilliform geometries. These virions are about 75 nm wide and 180 nm long. Rhabdoviruses have helical nucleocapsids and their genomes are linear, around 11–15 kb in length. Rhabdoviruses carry their genetic material in the form of negative-sense single-stranded RNA. They typically carry genes for five proteins: large protein (L), glycoprotein (G), nucleoprotein (N), phosphoprotein (P), and matrix protein (M). Rhabdoviruses that infect vertebrates (especially mammals and fishes), plants, and insects are usually bullet-shaped. However, in contrast to paramyxoviruses, rhabdoviruses do not have hemagglutinating and neuraminidase activities.
Table legend: "*" denotes type species.
Transcriptase of rhabdovirus is composed of 1 L and 3 P proteins. Transcriptase components are always present in the complete virion to permit rhabdoviruses to begin transcription immediately after entry.
The rhabdovirus ranscriptase proceeds in a 3' to 5' direction on the genome and the transcription terminates randomly at the end of protein sequences. For example, if a transcription finishes at the end of M sequence; leader RNA and N, P and M mRNAs are formed separately from each other.
Also, mRNAs accumulate according to the order of protein sequences on the genome, solving the logistics problem in the cell. For example, N protein is necessary in high quantities for the virus, as it coats the outside of the replicated genomes completely. Since the N protein sequence is located at the beginning of the genome (3' end) after the leader RNA sequence, mRNAs for N protein can always be produced and accumulate in high amounts with every termination of transcription. After the transcription processes, all of the mRNAs are capped at the 5' end and polyadenylated at the 3' end by L protein.
This transcription mechanism thus provides mRNAs according to the need of the viruses.
The virus proteins translated on free ribosomes but G protein is translated by the rough endoplasmic reticulum. This means G protein has a signal peptide on its mRNA's starting codes. Phosphoproteins(P) and glycoprotein(G) undergo post-translational modification. Trimers of P protein are formed after phosphorylation by kinase activity of L protein. The G protein is glycosylated in the rough endoplasmic reticulum and the Golgi complex.
Viral replication is cytoplasmic. Entry into the host cell is achieved by attachment of the viral G glycoproteins to host receptors, which mediates clathrin-mediated endocytosis. Replication follows the negative stranded RNA virus replication model. Negative stranded RNA virus transcription, using polymerase stuttering is the method of transcription. The virus exits the host cell by budding, and tubule-guided viral movement. Transmission routes are zoonosis and bite.
Replication of many rhabdoviruses occurs in the cytoplasm, although several of the plant infecting viruses replicate in the nucleus.. In order for replication, both the L and P protein must be expressed to regulate transcription. The L protein have a lot of enzymatic actiivites such as RNA replication, capping mRNAs phospholorylation of P. L protein gives feature in about replication in cytopolasm. Transcription results in five monocistronic mRNAs being produced because the intergenic sequences act as both termination and promoter sequences for adjacent genes. This type of transcription mechanism is explained by stop-start model( stuttering transcription). Owing to stop-start model, the large amounts of the structural proteins are produced. According to this model, the virus-associated RNA polymerase starts firstly the synthesis of leader RNA and then the five mRNA which will produce N, P, M, G, L proteins, respectively. After the leader RNA was produced, the polymerase enzyme reinitiates virion transcription on N gene and proceeds its synthesis until it ends 3′ end of the chain.Then, the synthesis of P mRNAs are made by same enzyme with new starter sinyal. These steps continue until the enzyme arrives the end of the L gene. During transcription process, the polymerase enzyme may leave the template at any point and then bound just at the 3′ end of the genome RNA to start mRNA synthesis again. This process will results concentration gradient of the amount of mRNA based on its place and its range from the 3′ end. In the circumstances, the amounts of mRNA species change and will be produced N>P>M>G>L proteins. During their synthesis the mRNAs are processed to introduce a 5' cap and a 3’ polyadenylated tail to each of the molecules .This structure is homologous to cellular mRNAs and can thus be translated by cellular ribosomes to produce both structural and non-structural proteins.
Genomic replication requires a source of newly synthesized N protein to encapsidate the RNA. This occurs during its synthesis and results in the production of a full length anti-genomic copy. This in turn is used to produce more negative-sense genomic RNA. The viral polymerase is required for this process, but how the polymerase engages in both mRNA synthesis and genomic replication is not well understood.
Replication characteristically occurs in an inclusion body within the cytoplasm, from where they bud through various cytoplasmic membranes and the outer membrane of the cell. This process results in the acquisition of the M + G proteins, responsible for the characteristic bullet- shaped morphology of the virus.
|Genus||Host details||Tissue tropism||Entry details||Release details||Replication site||Assembly site||Transmission|
|Lyssavirus||Humans; mammals||Neurons||Clathrin-mediated endocytosis||Budding||Cytoplasm||Cytoplasm||Zoonosis; animal bite|
|Novirhabdovirus||Fish||None||Clathrin-mediated endocytosis||Budding||Cytoplasm||Cytoplasm||Passive diffusion|
|Ephemerovirus||Cattle; mosquitoes||None||Clathrin-mediated endocytosis||Budding||Cytoplasm||Cytoplasm||Arthropod bite|
|Tibrovirus||Bovine||None||Clathrin-mediated endocytosis||Budding||Cytoplasm||Cytoplasm||Zoonosis; arthropod bite: midges|
|Nucleorhabdovirus||Plants||None||Viral movement; mechanical inoculation||Viral movement||Nucleus||Nucleus||Arthropod bite|
|Vesiculovirus||Human; cattle; horse; swine; sandflies; blackflies||Neurons||Clathrin-mediated endocytosis||Budding||Cytoplasm||Cytoplasm||Zoonosis; arthropod bite: sandflies|
|Cytorhabdovirus||Humans; cattle; rodents||None||Clathrin-mediated endocytosis; viral movement; mechanical inoculation||Budding; viral movement||Cytoplasm||Cytoplasm||Mechanical inoculation: aphid; mechanical inoculation: leafhopper; mechanical inoculation: planthopper|
These viruses fall into four groups based on the RNA polymerase gene. The basal clade appears to be novirhabdoviruses, which infect fish. Cytorhabdoviruses and the nucleorhabdoviruses, which infect plants, are sister clades. Lyssaviruses form a clade of their own which is more closely related to the land vertebrate and insect clades than to the plant viruses. The remaining viruses form a number of highly branched clades and infect arthropods and land vertebrates.
A 2015 analysis of 99 species of animal rhabdoviruses found that they fell into 17 taxonomic groupings, eight – Lyssavirus, Vesiculovirus, Perhabdovirus, Sigmavirus, Ephemerovirus, Tibrovirus, Tupavirus and Sprivivirus - which were previously recognized. The authors proposed seven new taxa on the basis of their findings: "Almendravirus", "Bahiavirus", "Curiovirus", "Hapavirus", "Ledantevirus", "Sawgravirus" and "Sripuvirus". Seven species did not group with the others suggesting the need for additional taxa.
"Curioviruses" a group of four viruses that were isolated from biting midges (Culicoides), sandflies (Lutzomyia ) and mosquitoes (Coqillettidia and Trichoprosopon) which were captured in the forests of South America and the Caribbean.
An unofficial supergroup – "Dimarhabdovirus" – refers to the genera Ephemerovirus and Vesiculovirus. A number of other viruses that have not been classified into genera also belong to this taxon. This supergroup contains the genera with species that replicate in both vertebrate and invertebrate hosts and have biological cycles that involve transmission by haematophagous dipterans.
Rhabdoviruses are important pathogens of animals and plants. Rhabdoviruses are transmitted to hosts by arthropods, such as aphids, planthoppers, leafhoppers, black flies, sandflies, and mosquitoes.
In September 2012, researchers writing in the journal PLOS Pathogens described a species of rhabdovirus, called Bas-Congo Virus or BASV, responsible for 4 cases of viral hemorrhagic fever in the Bas-Congo district in 2009. The 2 non-fatal cases occurred in healthcare workers treating the other 2, suggesting the possibility of person-to-person transmission.
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