Everything about Togavirus totally explained
The
Togaviridae are a family of
viruses, including the following genera:
The
Togaviridae family belong to group IV of the
Baltimore classification of viruses. The
genome is linear, single-stranded, positive sense
RNA that's 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 (65-70nm diameter), the
capsid within is
icosahedral, constructed of 240
monomers, having a triangulation number of 4. The
receptors for binding are unknown, however the
tropism is varied and it's 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
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 non-structural proteins responsible for
gene expression and
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 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, 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.Further Information
Get more info on 'Togavirus'.
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