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Flaviviridae

Article Discussion

Template:Short description Template:Virusbox

Flaviviridae is a family of enveloped positive-strand RNA viruses which mainly infect mammals and birds.<ref name=ICTVProfile>Template:Cite journal</ref> They are primarily spread through arthropod vectors (mainly ticks and mosquitoes).<ref name="ICTVReport" /> The family gets its name from the yellow fever virus; flavus is Latin for "yellow", and yellow fever in turn was named because of its propensity to cause jaundice in victims.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> There are 89 species in the family divided among four genera.<ref name="ICTVReport">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Diseases associated with the group include: hepatitis (hepaciviruses), hemorrhagic syndromes, fatal mucosal disease (pestiviruses), hemorrhagic fever, encephalitis, and the birth defect microcephaly (flaviviruses).<ref name="ViralZone">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

StructureEdit

Virus particles are enveloped and spherical with icosahedral-like geometries that have pseudo T=3 symmetry. They are about 40–60 nm in diameter.<ref name="ICTVReport" /><ref name="ViralZone" />

GenomeEdit

Template:Inline citations needed Members of the family Flaviviridae have monopartite, linear, single-stranded RNA genomes of positive polarity, and 9.6 to 12.3 kilobase in total length. The 5'-termini of flaviviruses carry a methylated nucleotide cap, while other members of this family are uncapped and encode an internal ribosome entry site.

The genome encodes a single polyprotein with multiple transmembrane domains that is cleaved, by both host and viral proteases, into structural and non-structural proteins. Among the non-structural protein products (NS), the locations and sequences of NS3 and NS5, which contain motifs essential for polyprotein processing and RNA replication respectively, are relatively well conserved across the family and may be useful for phylogenetic analysis.

Life cycleEdit

File:Pathogens-07-00068-g002.webp
Life cycle of Japanese encephalitis virus (JEV)

Viral replication is cytoplasmic. Entry into the host cell is achieved by attachment of the viral envelope protein E to host receptors, which mediates clathrin-mediated endocytosis. Replication follows the positive-stranded RNA virus replication model. Positive-stranded RNA virus transcription is the method of transcription. Translation takes place by viral initiation. The virion assembles by budding through intracellular membranes and exits the host cell by exocytosis.<ref name="ICTVReport" /><ref name="ViralZone" /><ref>Template:Cite journal</ref>

Host range and evolutionary historyEdit

A wide variety of natural hosts are used by different members of the Flaviviridae, including fish, mammals including humans and various invertebrates, such as those specific to mollusks and crustaceans.<ref name=lensink2022>Template:Cite journal</ref> The genomes of these flaviviruses show close synteny with that of the flavivirus type species, yellow fever virus.<ref name=parryasgari2019>Template:Cite journal</ref> One flavivirus, the Wenzhou shark flavivirus, infects both Pacific spadenose sharks (Scoliodon macrorhynchos) and Gazami crabs (Portunus trituberculatus) with overlapping ranges, raising the possibility of a two-host marine lifecycle.<ref name=lensink2022/> However, another clade of flavivirus, the insect-specific flaviviruses, have genomes that do not demonstrate strong synteny with any of these groups, suggesting a complex evolutionary history.<ref name="ICTVReport"/><ref>Template:Cite journal</ref>

Flavivirus endogenous viral elements, traces of flavivirus genomes integrated into the host's DNA, are found in many species, including a tadpole shrimp Lepidurus articus, the water flea Daphnia magna and a freshwater jellyfish Craspedacusta sowerbii,<ref name=parryasgari2019/> suggesting ancient coevolution between animal and flavivirus lineages.<ref name=lensink2022/><ref name=parryasgari2019/> Many of the well-known members of the family causing disease in vertebrates are transmitted via arthropod vectors (ticks and mosquitoes).<ref name="ICTVReport" /><ref name="ViralZone" /><ref name=parryasgari2019/>

TaxonomyEdit

File:Doi.org-10.7717-peerj.74-Fig-1-full.png
Phylogenetic tree of Flaviviridae using the NS3 protein sequences

The Flaviviridae are part of RNA virus supergroup II, which includes certain plant viruses and bacterial viruses.<ref name="ICTVReport" />

The family has four genera:<ref name="ICTVProfile" /><ref name="ICTVReport" />

Unclassified

Other Orthoflaviviruses are known that have yet to be classified. These include Wenling shark virus.

Jingmenvirus is a group of unclassified viruses in the family which includes Alongshan virus, Guaico Culex virus, Jingmen tick virus and Mogiana tick virus. These viruses have a segmented genome of four or five pieces. Two of these segments are derived from flaviviruses.Template:Citation needed

A number of viruses may be related to the flaviviruses, but have features that are atypical of the flaviviruses. These include citrus Jingmen-like virus, soybean cyst nematode virus 5, Toxocara canis larva agent, Wuhan cricket virus, and possibly Gentian Kobu-sho-associated virus.Template:Citation needed

Clinical importanceEdit

Major diseases caused by members of the family Flaviviridae include: Template:Columns-list

ReferencesEdit

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External linksEdit

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