| Togaviruses | |
|---|---|
Virus classification  | |
| (unranked): | Virus |
| Realm: | Riboviria |
| Phylum: | incertae sedis |
| Family: | Togaviridae |
| Genera | |
Togaviridae [1] is a family of RNA viruses. Humans, mammals, birds, and mosquitoes serve as natural hosts. Currently, 31 species are placed in this family in a single genus, Alphavirus . [2] Diseases associated with alphaviruses include arthritis and encephalitis. [1] [3]
Group: ssRNA(+)
The Togaviridae family belongs to group IV of the Baltimore classification of viruses. The genome is linear, nonsegmented, single-stranded, positive-sense RNA that is 10,000–12,000 nucleotides long. The 5'-terminus carries a methylated nucleotide cap and the 3'-terminus has a polyadenylated tail, therefore resembling cellular mRNA. The virus is enveloped and forms spherical particles (65–70 nm diameter), the capsid within is icosahedral, constructed of 240 monomers, having a triangulation number of 4. [1] [3] [4] [5]
| Genus | Structure | Symmetry | Capsid | Genomic arrangement | Genomic segmentation |
|---|---|---|---|---|---|
| Alphavirus | Icosahedral | T=4 | Enveloped | Linear | Monopartite |
Entry into the host cell is achieved by attachment of the viral E glycoprotein to host receptors, which mediates clathrin-mediated endocytosis. [1] [3] The receptors for binding are unknown, but the tropism is varied and the glycoprotein petal-like spikes are known to act as attachment proteins. After virus attachment and entry into the cell, gene expression and replication takes place within the cytoplasm. [4] [5]
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, and suppression of termination. The vector for the Togaviridae is primarily the mosquito, where replication of the virus occurs. The family Togaviridae is classified into Old World and New World viruses based on geographical distribution, although a few transoceanic crossings likely have occurred. [4] [5] Human, mammals, marsupials, birds, and mosquitoes serve as the natural host. Transmission routes are zoonosis, bite, and respiratory. [1] [3]
| Genus | Host details | Tissue tropism | Entry details | Release details | Replication site | Assembly site | Transmission |
|---|---|---|---|---|---|---|---|
| Alphavirus | Humans; mammals; marsupials; birds; mosquitoes | None | Clathrin-mediated endocytosis | Secretion | Cytoplasm | Cytoplasm | Zoonosis: arthropod bite |
The nonstructural proteins are encoded at the 5' end, formed during the first of two characteristic rounds of translation. These proteins are originally translated as a polyprotein, which consequently undergo self cleavage, forming four nonstructural proteins responsible for gene expression and replication. The formation of P1234 occurs due to a stop codon read-through, which has a 10% to 20% chance of occurrence. [6] Autoproteolytic activity of P2 enables cis cleavage of P1234 between P3 and P4, forming a P123 polyprotein and a nsP4 protein. The nsP4 protein is an RNA-dependent RNA polymerase and promotes further negative-strand RNA synthesis. This leads to the accumulation of P123 over time and once the concentration is high enough, all the other proteins are cleaved by the trans proteolytic activity of P2. Finally, the N-terminal of nsP4 is able to act as a scaffold and forms a complex with nsP1, nsP2, and nsP3 that then causes plus strand synthesis.
The formation of a subgenomic(dna)fragment, encoding the structural proteins and a negative-sense fragment, a template for further synthesis of positive-sense RNA, is the characteristic second phase of translation. Assembly takes place at the cell surface, where the virus buds from the cell, acquiring the envelope. The replication cycle is very fast, taking around 4 hours. [4] [5]
Initially, the Togaviridae family included what are now called the Flaviviruses , within the Alphavirus genus. The flaviviruses were formed into their own family when sufficient differences with the alphaviruses were noted due to the development of sequencing. [4] Rubella virus was formerly included in the family Togaviridae in its own genus Rubivirus, but is now classified in its own family Matonaviridae [7]
Chikungunya is an infection caused by the chikungunya virus (CHIKV). Symptoms include fever and joint pains. These typically occur two to twelve days after exposure. Other symptoms may include headache, muscle pain, joint swelling, and a rash. Symptoms usually improve within a week; however, occasionally the joint pain may last for months or years. The risk of death is around 1 in 1,000. The very young, old, and those with other health problems are at risk of more severe disease.
Flavivirus is a genus of viruses in the family Flaviviridae. This genus includes the West Nile virus, dengue virus, tick-borne encephalitis virus, yellow fever virus, Zika virus and several other viruses which may cause encephalitis, as well as insect-specific flaviviruses (ISFs) such as cell fusing agent virus (CFAV), Palm Creek virus (PCV), and Parramatta River virus (PaRV).
Arbovirus is an informal name used to refer to any viruses that are transmitted by arthropod vectors. The word arbovirus is an acronym. The word tibovirus is sometimes used to more specifically describe viruses transmitted by ticks, a superorder within the arthropods. Arboviruses can affect both animals and plants. In humans, symptoms of arbovirus infection generally occur 3–15 days after exposure to the virus and last three or four days. The most common clinical features of infection are fever, headache, and malaise, but encephalitis and hemorrhagic fever may also occur.
Rubella virus (RuV) is the pathogenic agent of the disease rubella, and is the main cause of congenital rubella syndrome when infection occurs during the first weeks of pregnancy.
Bunyavirales is an order of negative-sense single-stranded RNA viruses. It is the only order in the class Ellioviricetes. It was formerly known as Bunyaviridae family of viruses. The name Bunyavirales derives from Bunyamwera, where the original type species Bunyamwera orthobunyavirus was first discovered. Ellioviricetes is named in honor of late virologist Richard M. Elliott for his early work on bunyaviruses.
Ross River virus (RRV) is a small encapsulated single-strand RNA Alphavirus endemic to Australia, Papua New Guinea and other islands in the South Pacific. It is responsible for a type of mosquito-borne non-lethal but debilitating tropical disease known as Ross River fever, previously termed "epidemic polyarthritis". The virus is suspected to be enzootic in populations of various native Australian mammals, and has been found on occasion in horses.
Brome mosaic virus (BMV) is a small, positive-stranded, icosahedral RNA plant virus belonging to the genus Bromovirus, family Bromoviridae, in the Alphavirus-like superfamily.
The Semliki Forest virus was first isolated from mosquitoes in the Semliki Forest, Uganda by the Uganda Virus Research Institute in 1942 and described by Smithburn and Haddow. It is known to cause disease in animals including humans. It is an alphavirus found in central, eastern, and southern Africa.
Alphavirus is a genus of RNA viruses, the sole genus in the Togaviridae family. Alphaviruses belong to group IV of the Baltimore classification of viruses, with a positive-sense, single-stranded RNA genome. There are 31 alphaviruses, which infect various vertebrates such as humans, rodents, fish, birds, and larger mammals such as horses, as well as invertebrates. Transmission between species and individuals occurs mainly via mosquitoes, making the alphaviruses a member of the collection of arboviruses – or arthropod-borne viruses. Alphavirus particles are enveloped, have a 70 nm diameter, tend to be spherical, and have a 40 nm isometric nucleocapsid.
The Western equine encephalomyelitis virus is the causative agent of relatively uncommon viral disease Western equine encephalomyelitis (WEE). An alphavirus of the family Togaviridae, the WEE virus is an arbovirus transmitted by mosquitoes of the genera Culex and Culiseta. WEE is a recombinant virus between two other alphaviruses, an ancestral Sindbis virus-like virus, and an ancestral Eastern equine encephalitis virus-like virus. There have been under 700 confirmed cases in the U.S. since 1964. This virus contains an envelope that is made up of glycoproteins and nucleic acids. The virus is transmitted to people and horses by bites from infected mosquitoes and birds during wet, summer months.
Sindbis virus (SINV) is a member of the Togaviridae family, in the alphavirus subfamily. The virus was first isolated in 1952 in Cairo, Egypt. The virus is transmitted by mosquitoes SINV causes sindbis fever in humans and the symptoms include arthralgia, rash and malaise. Sindbis fever is most common in South and East Africa, Egypt, palestine, Philippines and parts of Australia. Sindbis virus is an "arbovirus" (arthropod-borne) and is maintained in nature by transmission between vertebrate (bird) hosts and invertebrate (mosquito) vectors. Humans are infected with Sindbis virus when bitten by an infected mosquito. SINV has been linked to Pogosta disease in Finland, Ockelbo disease in Sweden and Karelian fever in Russia.
Ochlerotatus is a genus of mosquito. Until 2000, it was ranked as a subgenus of Aedes, but after Reinert's work, the clade was upgraded to the level of a genus. This change has resulted in the renaming of many subgenus species, and many aedini-related taxa are undergoing taxonomic revisions. Some authors are still using traditional taxonomic names in their publications.
Mosquito-borne diseases or mosquito-borne illnesses are diseases caused by bacteria, viruses or parasites transmitted by mosquitoes. Nearly 700 million people get a mosquito-borne illness each year resulting in over one million deaths.
Mayaro virus disease is a mosquito-borne zoonotic pathogen endemic to certain humid forests of tropical South America. Infection with Mayaro virus causes an acute, self-limited dengue-like illness of 3–5 days' duration. The causative virus, abbreviated MAYV, is in the family Togaviridae, and genus Alphavirus. It is closely related to other alphaviruses that produce a dengue-like illness accompanied by long-lasting arthralgia. It is only known to circulate in tropical South America.
Eilat virus (EILV) is a unique Alphavirus which is known mainly for its host range restriction generally to insects by means of RNA replication. The virus found in the Negev desert. It is incapable of infecting vertebrate cells, differentiating it from other alphaviruses.
West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family Flaviviridae, specifically from the genus Flavivirus, which also contains the Zika virus, dengue virus, and yellow fever virus. West Nile virus is primarily transmitted by mosquitoes, mostly species of Culex. The primary hosts of WNV are birds, so that the virus remains within a "bird–mosquito–bird" transmission cycle.
Middelburg virus (MIDV) is an Alphavirus of the Old World Group that has likely endemic and zoonotic potential... It is of the viral family Togaviridae. It was isolated from mosquitos in 1957 in South Africa, MDIV antigens have now been found in livestock, horses, and humans [1].
Yokose virus (YOKV) is in the genus Flavivirus of the family Flaviviridae. Flaviviridae are often found in arthropods, such as mosquitoes and ticks, and may also infect humans. The genus Flavivirus includes over 50 known viruses, including Yellow Fever, West Nile Virus, Zika Virus, and Japanese Encephalitis. Yokose virus is a new member of the Flavivirus family that has only been identified in a few bat species. Bats have been associated with several emerging zoonotic diseases such as Ebola and SARS.
Sepik virus (SEPV) is an arthropod-borne virus (arbovirus) of the genus Flavivirus and family Flaviviridae. Flaviviridae is one of the most well characterized viral families, as it contains many well-known viruses that cause diseases that have become very prevalent in the world, like Chikungunya virus and Dengue virus. The genus Flavivirus is one of the largest viral genera and encompasses over 50 viral species, including tick and mosquito borne viruses like Yellow fever virus and West Nile virus. Sepik virus is much less well known and has not been as well-classified as other viruses because it has not been known of for very long. Sepik virus was first isolated in 1966 from the mosquito Mansoniaseptempunctata, and it derives its name from the Sepik River area in Papua New Guinea, where it was first found. The geographic range of Sepik virus is limited to Papua New Guinea, due to its isolation.
Note that 'Ochlerotatus vigilax' prior to 2000, was known as 'Aedes vigilax'