Togaviridae

All togaviruses (from lat. toga= coat), are enveloped viruses about 60-70nm in size. They contain a single (linear) strand of positive sense RNA ((+)ssRNA). At the 5' end of the RNA strand is a 5' cap structure. This is followed by the sequences for the usually four non-structural proteins (nsP1-4), the structural proteins (CP, E1, E2) and at the 3' end a poly(A) tail. This allows the genome to act as a messenger RNA (mRNA) for translation. The genome is packaged in an icosahedral capsid formed from homodimers of capsid protein C. In the lipid envelope are found the two structural proteins E1 and E2, which are hetrodimeric to spikes and in turn are formed into trimers. Within the genus Alphavirus up to 80 trimers are found. The E1 glycoprotein is responsible for adsorption to the target cell. In some alphaviruses, E3, a third envelope protein (10 kDa), may also be involved. Virion-associated lipids, which are required for the envelope of the virus, are derived from host cell membranes during the process of virus maturation. These lipids make up about 30% of the total weight of the virion and their composition varies with the cell from which the virions were derived.

The family Togaviridae (Togaviruses) currently includes two genera of enveloped viruses:

• Rubivirus (The genus Rubivirus was placed by the ICTV 2018/2019 in a separate family Matonaviridae, since March 2020 order Hepelivirales in the same class). The genus Rubivirus recognizes only one species, rubellavirus (rubellavirus, RUBV). RUBV appears to infect mammals only by the respiratory route, but tends to develop persistent infections, unlike alphaviruses, which are cytopathic to vertebrate cells. The genomic RNA and nucleocapsid core is covered by a lipid bilayer containing heterodimers of the two virally encoded glycoproteins E2 and E1, which form a regular icosedric surface lattice.
• Alphavirus(formerly: arbovirus A): This includes >25 species with numerous geographic variants; they cause a wide range of diseases in humans, most of which occur as travelers' diseases in Europe. Alphaviruses are largely arthropod viruses that replicate in their invertebrate vectors as well as in their vertebrate hosts.

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Replication: Togaviruses attach to the cell surface via specific receptors and are taken up by a forming endosomal vesicle. A single cellular receptor for viral adsorption is not known to date. After adsorption, the virus is taken up via endocytosis. Inside the endosome, the outer domains of the E1-/Es proteins are now rearranged at acidic pH. They mediate and the fusion of endosomal membrane and viral envelope. This allows the capsid to be released into the cytosol. It disintegrates and releases the genome. The ORF1 of the viral genome is transcribed from the 5` end. In contrast, the sequences for the structural proteins are first amplified by the viral RNA polymerase (replicase) via a complementary (-)ssRNA as a template and translated as a separate short mRNA. After synthesis of the new genomic RNA and viral structural proteins, transport of the glycosylated coat proteins begins from the endoplasmic reticulum (ER) via the Golgi apparatus to the cell membrane. Here, the assembly of the envelope and capsid finally takes place. The subsequent budding process leads to the release of new virus particles.

In the case of alphaviruses, the capsid with the RNA is already formed beforehand; in the case of rubellavirus, capsid formation only begins with the attachment predominantly to the membrane of the endoplasmic reticulum, from which the budding of the rubellavirus also occurs.

The classification of the Togaviridae follows the guidelines of the International Committee on Taxonomy of Viruses (ICTV; 02/2019)

Genus Rubivirus

• Rubellvirus

Genus Alphavirus (formerly Arbovirus A)

Group Barmah Forest virus complex' (BFV complex)

• Barmah Forest Virus (BFV)

Eastern equine encephalitis complex' group (EEEV group)

• Eastern equine encephalomyelitis virus (also Eastern equine encephalitis virus, en. Eastern equine encephalitis virus, EEEV)

Group Middelburg virus complex' (MIDV complex)

• Middleburg virus (MIDV)

Group Ndumu virus complex' (NDUV complex)

• Ndumu virus (NDUV)

Group Semliki Forest virus complex (SFV complex)

• Bebaru virus
• Chikungunya virus (CHIKV)
• Getah virus (GETV)
• Mayaro virus (MAYV)
• O'nyong-nyong virus (ONNV)
• Ross River virus (RRV)
• Semliki Forest Virus (SFV)

Venezuelan equine encephalitis complex' group (VEEV group)

• Cabassou virus (CABV)
• Everglades virus (EVEV)
• Mosso das Pedras virus (MDPV)
• Mucambo virus (MUCV)
• Paramana virus
• Pixuna virus (PIXV)
• Rio Negro virus (RNV)
• Trocara virus
• VEE virus (VEEV)

Western equine encephalitis complex' group (WEEV group)

• Aura virus
• Sindbis virus (SINV)
• Whataroa virus
• Fort Morgan virus (old Buggy Creek virus, FMV)
• Highlands J virus (HJV)
• Western equine encephalomyelitis virus (also Western equine encephalitis virus, en. Western equine encephalitis virus, WEEV)

without proposed group:

• Eilat virus (EILV)
• Mwinilunga virus' (MWAV)
• Salmon pancreas disease virus (SPDV)
• Rainbow trout sleeping disease virus' (RTSDV)
• Southern elephant seal virus (SESV)
• Tonate virus (TONV)
• Una virus (UNAV)
• Triniti virus' (TNTV)