Togaviridae 1582914 204765084 2008-04-10T20:01:02Z GregorB 179697 /* History */ Bulleted list {{Taxobox | color=violet | name = Togaviruses | virus_group = iv | familia = '''''Togaviridae''''' | subdivision_ranks = Genera | subdivision = ''[[Alphavirus]]''<br> ''[[Rubivirus]]'' }} The '''''Togaviridae''''' are a family of [[virus]]es, including the following genera: *Genus ''[[Alphavirus]]''; type species: ''[[Sindbis virus]]'', [[Eastern equine encephalitis virus]], [[Western equine encephalitis virus]], [[Venezuelan equine encephalitis virus]], [[Ross River virus]], [[O'nyong'nyong virus]] *Genus ''[[Rubivirus]]''; type species: ''[[Rubella]] virus'' The ''Togaviridae'' [[family]] belong to group IV of the [[Baltimore classification]] of viruses. The [[genome]] is linear, 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 [[Envelope (biology)|enveloped]] and forms [[spherical]] particles (65-70nm diameter), the [[capsid]] within is [[icosahedral]], constructed of 240 [[monomer]]s, having a triangulation number of 4. The [[Receptor (biochemistry)|receptor]]s for binding are unknown, however the [[tropism]] is varied and it is known that the [[glycoprotein]] spikes act as attachment proteins. After virus attachment and entry into the cell, gene expression and replication takes place within the [[cytoplasm]]. ===Genome replication=== The non-structural [[protein]]s 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 non-structural proteins responsible for [[gene expression]] and [[DNA replication|replication]]. 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 (genetics)|Assembly]] takes place at the cell surface, where the virus [[Budding#In virology|bud]]s 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 [[Flaviviridae|Flaviviruses]], within the [[Alphavirus]] genus. The Flaviviruses were formed into their own family when sufficient differences with the Alphaviruses were noted. * Early 1800s - Rubella is identified as a distinct disease * 1930 - Western Equine Encephalitis virus is first isolated in the United States (the first alphavirus ever isolated) * 1933 - Eastern Equine Encephalitis virus is first isolated in the United States. * 1938 - Venezuelan Equine Encephalitis is isolated. * 1941 - Western Equine Encephalitis epidemic 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. * 1942 - Semliki Forest virus is isolated in Buliyama, Bwamba County, Uganda. * 1952 - Sindbis virus is isolated in the Sindbis health district, 40 miles north of Cairo, Egypt. * 1959 - Ross River virus is isolated from ''Aedes vigilax'' mosquitoes which were trapped at the Ross River in Australia. * 1962 - Rubella virus is isolated in culture. * 1963 - Ross River virus, which causes epidemic polyarthritis (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 is licensed * 1971 - Last epidemic of Venezuelan equine encephalitis is seen in horses in southern Texas. * 1972 - The rubella vaccine is combined with the measles and mumps vaccines to form the Measles/Mumps/Rubella (MMR) vaccine. * 1986 - Barmah Forest virus 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 of the glycoprotein shell of the Semliki Forest virus. * 2005-2006 - Large epidemic of the chikungunya virus on the island of La Re´union and the surrounding islands in the Indian Ocean. * 2006 - Major epidemic of the chikungunya virus in India with over 1.5 million cases reported. ==References== *[http://www-micro.msb.le.ac.uk/3035/Togaviruses.html University of Leicester, Microbiology] *[http://www.stanford.edu/group/virus/toga/class.html Stanford University] *Murray, et al, ''Medical Microbiology'', 5th Edition, Philadelphia, Elsevier Mosby 2005 ISBN 0-323-03325-3 [[Category:Viruses]] [[Category:Togaviruses|*]] [[da:Togaviridae]] [[de:Togaviridae]] [[es:Togaviridae]] [[fr:Togaviridae]] [[ja:トガウイルス科]] [[pl:Togawirusy]] [[ro:Togaviridae]]