Togaviridae
Encyclopedia
The Togaviridae are a family of virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

es, including the following genera:
  • Genus Alphavirus
    Alphavirus
    In biology and immunology, an alphavirus belongs to the group IV Togaviridae family of viruses, according to the system of classification based on viral genome composition introduced by David Baltimore in 1971. Alphaviruses, like all other group IV viruses have a positive sense single stranded RNA...

    ; type species: Sindbis virus
    Sindbis virus
    Sindbis Virus 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...

    , Eastern equine encephalitis virus
    Eastern equine encephalitis virus
    Eastern equine encephalitis virus , commonly called sleeping sickness or Triple E, is a zoonotic alphavirus and arbovirus present in North, Central and South America and the Caribbean. EEE was first recognized in Massachusetts, USA in 1831 when 75 horses died of encephalitic illness...

    , Western equine encephalitis virus
    Western equine encephalitis virus
    The Western equine encephalomyelitis virus is the causative agent of relatively uncommon viral disease Western equine encephalomyelitis . An Alphavirus of the family Togaviridae, the WEE virus is an arbovirus transmitted by mosquitoes of the genera Culex and Culiseta...

    , Venezuelan equine encephalitis virus
    Venezuelan equine encephalitis virus
    Venezuelan equine encephalitis virus is a mosquito-borne viral pathogen that causes Venezuelan equine encephalitis or encephalomyelitis . VEE can affect all equine species, such as horses, donkeys, and zebras. After infection, equines may suddenly die or show progressive central nervous system...

    , Ross River virus
    Ross River virus
    Ross River virus 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...

    , O'nyong'nyong virus
    O'nyong'nyong virus
    The O'nyong'nyong virus or O'nyong-nyong virus is a virus first isolated by the Uganda Virus Research Institute in Entebbe, Uganda in 1959. It is a togavirus , genus Alphavirus and is closely related to the Chikungunya and Igbo Ora viruses. The name comes from the Nilotic language of Uganda and...

    , Chikungunya
    Chikungunya
    Chikungunya virus is an insect-borne virus, of the genus Alphavirus, that is transmitted to humans by virus-carrying Aedes mosquitoes. There have been recent breakouts of CHIKV associated with severe illness...

  • Genus Rubivirus; type species: Rubella virus
    Rubella virus
    Rubella virus is the pathogenic agent of the disease Rubella, and is the cause of congenital rubella syndrome when infection occurs during the first weeks of lunacy.Humans are the only known host of this virus....



The Togaviridae family
Family
In human context, a family is a group of people affiliated by consanguinity, affinity, or co-residence. In most societies it is the principal institution for the socialization of children...

 belong to group IV of the Baltimore classification
Baltimore classification
The Baltimore classification, developed by David Baltimore, is a virus classification system that groups viruses into families, depending on their type of genome and their method of replication....

 of viruses. The genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

 is linear, single-stranded, positive sense RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

 that is 10,000-12,000 nucleotides long. The 5'-terminus carries a methylated nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...

 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
Capsid
A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...

 within is icosahedral, constructed of 240 monomer
Monomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...

s, having a triangulation number of 4. The receptors
Receptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...

 for binding are unknown, however the tropism
Tropism
A tropism is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In tropisms, this response is dependent on the direction of the stimulus...

 is varied and it is known that the glycoprotein
Glycoprotein
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...

 spikes act as attachment proteins. After virus attachment and entry into the cell, gene expression and replication takes place within the cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...

. The vector for Togaviridæ is primarily the mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...

, where replication of the virus occurs.

Genome replication

The non-structural protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s are encoded at the 5’ end, formed during the first of two characteristic rounds of translation
Translation
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. Whereas interpreting undoubtedly antedates writing, translation began only after the appearance of written literature; there exist partial translations of the Sumerian Epic of...

. These proteins are originally translated as a polyprotein, which consequently undergo self cleavage
Cleavage
Cleavage may refer to:*Cleavage , partial exposure of the separation between a woman's breasts.**Cleavage enhancement, methods of making a person's breast cleavage look more substantial than it really is....

, forming four non-structural proteins responsible for gene expression
Gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

 and replication
DNA replication
DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...

. The formation of a sub-genomic fragment, encoding the structural proteins and a negative sense fragment, a template for further synthesis of positive sense RNA are 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.

History

Initially the Togavirus family included what are now called the Flaviviruses
Flaviviridae
The Flaviviridae are a family of viruses that are primarily spread through arthropod vectors . The family gets its name from Yellow Fever virus, a type virus of Flaviviridae; flavus means yellow in Latin...

, within the Alphavirus
Alphavirus
In biology and immunology, an alphavirus belongs to the group IV Togaviridae family of viruses, according to the system of classification based on viral genome composition introduced by David Baltimore in 1971. Alphaviruses, like all other group IV viruses have a positive sense single stranded RNA...

 genus. The Flaviviruses were formed into their own family when sufficient differences with the Alphaviruses were noted.
  • Early 19th century - Rubella
    Rubella
    Rubella, commonly known as German measles, is a disease caused by the rubella virus. The name "rubella" is derived from the Latin, meaning little red. Rubella is also known as German measles because the disease was first described by German physicians in the mid-eighteenth century. This disease is...

     is identified as a distinct disease

  • 1930 - Western Equine Encephalitis
    Western equine encephalitis virus
    The Western equine encephalomyelitis virus is the causative agent of relatively uncommon viral disease Western equine encephalomyelitis . An Alphavirus of the family Togaviridae, the WEE virus is an arbovirus transmitted by mosquitoes of the genera Culex and Culiseta...

     virus is first isolated in the United States (the first alphavirus ever isolated)

  • 1933 - Eastern Equine Encephalitis
    Eastern equine encephalitis virus
    Eastern equine encephalitis virus , commonly called sleeping sickness or Triple E, is a zoonotic alphavirus and arbovirus present in North, Central and South America and the Caribbean. EEE was first recognized in Massachusetts, USA in 1831 when 75 horses died of encephalitic illness...

     virus is first isolated in the United States.

  • 1938 - Venezuelan Equine Encephalitis
    Venezuelan equine encephalitis virus
    Venezuelan equine encephalitis virus is a mosquito-borne viral pathogen that causes Venezuelan equine encephalitis or encephalomyelitis . VEE can affect all equine species, such as horses, donkeys, and zebras. After infection, equines may suddenly die or show progressive central nervous system...

     is isolated.

  • 1941 - Western Equine Encephalitis epidemic
    Epidemic
    In epidemiology, an epidemic , occurs when new cases of a certain disease, in a given human population, and during a given period, substantially exceed what is expected based on recent experience...

     is seen in the United States. It affects 300,000 horses and 3,336 humans.

  • 1941 - Normann Gregg notices large number of children with cataracts following a rubella outbreak. This and other defects are then categorized under the congenital rubella syndrome
    Congenital rubella syndrome
    Congenital rubella syndrome can occur in a developing fetus of a pregnant woman who has contracted rubella during her first trimester. If infection occurs 0–28 days before conception, there is a 43% chance the infant will be affected. If the infection occurs 0–12 weeks after conception, there is a...

    .

  • 1942 - Semliki Forest virus
    Semliki Forest Virus
    The Semliki Forest virus was first isolated from mosquitoes in the Semliki Forest, Uganda by the Uganda Virus Research Institute in 1942. It is known to cause disease in both animals and man...

     is isolated in Buliyama, Bwamba County, Uganda
    Uganda
    Uganda , officially the Republic of Uganda, is a landlocked country in East Africa. Uganda is also known as the "Pearl of Africa". It is bordered on the east by Kenya, on the north by South Sudan, on the west by the Democratic Republic of the Congo, on the southwest by Rwanda, and on the south by...

    .

  • 1952 - Sindbis virus
    Sindbis virus
    Sindbis Virus 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...

     is isolated in the Sindbis health district, 40 miles north of Cairo, Egypt
    Cairo
    Cairo , is the capital of Egypt and the largest city in the Arab world and Africa, and the 16th largest metropolitan area in the world. Nicknamed "The City of a Thousand Minarets" for its preponderance of Islamic architecture, Cairo has long been a centre of the region's political and cultural life...

    .

  • 1959 - Ross River virus
    Ross River virus
    Ross River virus 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...

     is isolated from Aedes vigilax mosquitoes (now known as Ochlerotatus
    Ochlerotatus
    Ochlerotatus is a genus of mosquito. It was formerly part of Aedes, but now they are two separate genera....

     vigilax) which were trapped at the Ross River in Australia.

  • 1962 - Rubella virus
    Rubella virus
    Rubella virus is the pathogenic agent of the disease Rubella, and is the cause of congenital rubella syndrome when infection occurs during the first weeks of lunacy.Humans are the only known host of this virus....

     is isolated in culture
    Microbiological culture
    A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory conditions. Microbial cultures are used to determine the type of organism, its abundance in the sample being tested,...

    .

  • 1963 - Ross River virus, which causes epidemic polyarthritis
    Epidemic polyarthritis
    Epidemic polyarthritis is an outdated term that was used to refer to polyarthritis caused by two mosquito-borne viruses endemic to Australasia:*Barmah Forest virus, which causes Barmah Forest Fever*Ross River virus , which causes Ross River Fever...

     (mostly seen in Australia), is isolated by Doherty and colleagues.

  • 1964 - The last major epidemic of Rubella in the United States is seen. Approximately 20,000 infants are left with permanent damage following in-utero rubella exposure.

  • 1969 - Rubella vaccine
    Rubella vaccine
    Rubella vaccine is a vaccine used against rubella.One form is called "Meruvax"....

     is licensed

  • 1971 - Last epidemic of Venezuelan equine encephalitis is seen in horses in southern Texas
    Texas
    Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

    .

  • 1972 - The rubella vaccine is combined with the measles and mumps vaccines to form the Measles, Mumps and Rubella
    MMR vaccine
    The MMR vaccine is an immunization shot against measles, mumps, and rubella . It was first developed by Maurice Hilleman while at Merck in the late 1960s....

     (MMR) vaccine.

  • 1986 - Barmah Forest virus
    Barmah Forest virus
    Barmah Forest virus is a virus currently found only in Australia. According to a Queensland Public Health Services fact sheet, "there is no specific drug treatment" for the virus, but the disease is non-fatal and relatively mild. The virus is transmitted to humans by bites from infected...

     is identified as causing human disease in Australia.

  • 1991-92 - Most recent worldwide epidemic of rubella. Probably due to vaccine failures and missed vaccinations.

  • 2001 - Scientists solved the crystal structure
    Crystal structure
    In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...

     of the glycoprotein shell of the Semliki Forest virus
    Semliki Forest Virus
    The Semliki Forest virus was first isolated from mosquitoes in the Semliki Forest, Uganda by the Uganda Virus Research Institute in 1942. It is known to cause disease in both animals and man...

    .

  • 2005-2006 - Large epidemic of the chikungunya virus on the island of La Réunion
    Réunion
    Réunion is a French island with a population of about 800,000 located in the Indian Ocean, east of Madagascar, about south west of Mauritius, the nearest island.Administratively, Réunion is one of the overseas departments of France...

     and the surrounding islands in the Indian Ocean
    Indian Ocean
    The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

    .

  • 2006 - Major epidemic of the chikungunya virus in India with over 1.5 million cases reported.

External links

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