In biology and immunology, an alphavirus (pronounced alph-AV-ir-rus) 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 genome. There are 27 alphaviruses, able to infect various vertebrates such as humans, rodents, birds, and larger mammals such as horses as well as invertebrates. Transmission between species and individuals occurs via mosquitoes making the alphaviruses a contributor to the collection of Arboviruses – or Arthropod Borne Viruses. Alphaviruses particles are enveloped have a 70nm diameter, tend to be spherical (although slightly pleomorphic), and have a 40nm isometric nucleocapsid. Image File history File links No higher resolution available. ... Virus classification involves naming and placing viruses into a taxonomic system. ... An RNA virus is a virus that either uses RNA as its genetic material, or whose genetic material passes through an RNA intermediate during replication. ... Genera Alphavirus Rubivirus The Togaviridae are a family of viruses, including the following genera: Genus Alphavirus; type species: Sindbis virus, Eastern equine encephalitis virus, Western equine encephalitis virus, Ross River virus, Onyongnyong virus Genus Rubivirus; type species: Rubella virus The genome of the Togaviridae viruses is a linear... Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology (from Greek: βίος, bio, life; and λόγος, logos, knowledge), also referred to as the biological sciences, is the study of living organisms utilizing the scientific method. ... Immunology is a broad branch of biomedical science that covers the study of all aspects of the immune system in all organisms. ... Genera Alphavirus Rubivirus The Togaviridae are a family of viruses, including the following genera: Genus Alphavirus; type species: Sindbis virus, Eastern equine encephalitis virus, Western equine encephalitis virus, Ross River virus, Onyongnyong virus Genus Rubivirus; type species: Rubella virus The genome of the Togaviridae viruses is a linear... Stop editing pages god ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... Ribonucleic acid or RNA is a nucleic acid polymer consisting of nucleotide monomers that plays several important roles in the processes that translate genetic information from deoxyribonucleic acid (DNA) into protein products; RNA acts as a messenger between DNA and the protein synthesis complexes known as ribosomes, forms vital portions... Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... Invertebrate is a term coined by Chevalier de Lamarck to describe any animal without a backbone or vertebra, like insects, squids and worms. ... Arbovirus is a shortened name given to viruses that are transmitted by arthropods, or arthropod-borne viruses [1]. Some Arboviruses are able to cause emergent diseases. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ...

Genome

The genome of alphaviruses consists of a single stranded positive sense RNA. The total genome length ranges between 11,000 and 12,000 nucleotides, and has a 5’ cap, and 3’ poly-A tail. There are two open reading frames (ORF’s) in the genome, non-structural and structural. The first is non structural and encodes proteins for transcription and replication of viral RNA, and the second encodes four structural proteins: Capsid protein C, Envelope glycoprotein E1, Envelope glycoprotein E2, and Envelope glycoprotein E3. The expression of these proteins and replication of the viral genome all takes place in the cytoplasm of the host cells. Polyadenylation is the covalent linkage of a polyadenylyl moiety to a messenger RNA molecule. ... An open reading frame or ORF is a portion of an organisms genome which contains a sequence of bases that could potentially encode a protein. ... A capsid is the outer shell of a virus. ... Organelles. ...

Alphavirus pathogenesis and the Immune response

The infection is spread by insect vectors such as mosquitoes. Once a human is bit by the infected mosquito, the virus can gain entry into the bloodstream, causing viremia. The alphavirus can also get into the CNS where it is able to grow and multiply within the neurones. This can lead to encephalitis, which can be fatal. When an individual is infected with this particular virus, its immune system can play a role in clearing away the virus particles. Alphaviruses are able to cause the production of interferons. Antibodies and T cells are also involved. The neutralising antibodies also play an important role to prevent further infection and spread.

Diagnosis, prevention and control

A patient can be diagnosed with the infection based on clinical samples from which the virus can be easily isolated and identified. Although a vaccine exists, it is only used with individuals who are more likely to come into contact with the virus such as those working in the laboratory and in regions where an epidemic is more likely to occur. Control procedures could also be put in place for example using specific sprays against the mosquito and its larvae.

Alphaviruses In Medicine

There are many alphaviruses distributed around the world with the ability to cause human disease. Infectious arthritis, encephalitis, rashes and fever being the most commonly observed. Larger mammals such as humans and horses are usually dead-end hosts or play a minor role in viral transmission, however in the case of Venezuelan equine encephalitis the virus is mainly amplified in horses. In most other cases the virus is maintained in nature in mosquitoes, rodents and birds. Arthritis (from Greek arthro-, joint + -itis, inflammation; plural: arthritides) is a group of conditions where there is damage caused to the joints of the body. ... Encephalitis is an acute inflammation of the brain, commonly caused by a viral infection. ... For the manga by Tsukasa Hôjô, see Rash. ... This article needs additional references or sources for verification. ...

For other uses, see Europe (disambiguation). ... A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ... The Semliki Forest Virus was first isolated from mosquitoes in the Semliki Forest, Uganda by the Uganda Virus Research Institute in 1944. ... Onyongnyong virus was first isolated by the Uganda Virus Research Institute in Entebbe, Uganda. ... Families 15, See classification A primate is any member of the biological order Primates, the group that contains all the species commonly related to the lemurs, monkeys, and apes, with the latter category including humans. ... Chikungunya is a rare form of viral fever caused by an alphavirus that is spread by mosquito bites from the Aedes aegypti mosquito. ... Location of Southeast Asia Southeast Asia is a subregion of Asia. ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... Ross River virus (RRV) is an arbovirus of the genus Alphavirus. ... For other uses, see Oceania (disambiguation). ... Eastern equine encephalomyelitis virus (EEE), commonly called sleeping sickness or Triple E, is a zoonotic alphavirus and arbovirus present in North, Central and South America and the Caribbean. ... World map showing the Americas CIA political map of the Americas The Americas are the lands of the Western hemisphere or New World consisting of the continents of North America[1] and South America with their associated islands and regions. ... Western equine encephalitis (WEE) is a relatively uncommon viral infection caused by the WEE virus, an Alphavirus of the family Togaviridae. ... North America North America is a continent[1] in the Earths northern hemisphere and (chiefly) western hemisphere. ... Venezuelan equine encephalitis virus is a mosquito-borne viral pathogen that causes Venezuelan equine encephalitis or encephalomyelitis (VEE). ... Suborders Sciuromorpha Castorimorpha Myomorpha Anomaluromorpha Hystricomorpha Rodentia is an order of mammals also known as rodents. ...

Alphaviruses In Research

Alphaviruses are of interest to gene therapy researchers, in particular the Ross River virus, Sindbis virus, Semliki Forest virus, and Venezuelan Equine Encephalitis virus have all been used to develop viral vectors for gene delivery. Of particular interest are the chimeric viruses that may be formed with alphaviral envelopes and retroviral capsids. Such chimeras are termed pseudotyped viruses. Alphaviral envelope pseudotypes of retroviruses or lentiviruses are able to integrate the genes that they carry into the expansive range of potential host cells that are recognized and infected by the alphaviral envelope proteins E2 and E1. The stable integration of viral genes is mediated by the retroviral interiors of these vectors. There are limitations to the use of alphaviruses in the field of gene therapy due to their lack of targeting, however, through the introduction of variable antibody domains in a non-conserved loop in the structure of E2, specific populations of cells have been targeted. Furthermore, the use of whole alphaviruses for gene therapy is of limited efficacy both because several internal alphaviral proteins are involved in the induction of apoptosis upon infection and also because the alphaviral capsid mediates only the transient introduction of mRNA into host cells. Neither of these limitations extend to alphaviral envelope pseudotypes of retroviruses or lentiviruses. However, the expression of Sindbis virus envelopes may lead to apoptosis, and their introduction into host cells upon infection by Sindbis virus envelope pseudotyped retroviruses may also lead to cell death. The toxicity of Sindbis viral envelopes may be the cause of the very low production titers realized from packaging cells constructed to produce Sindbis pseudotypes. Another branch of research involving alphaviruses is in vaccination. Alphaviruses are apt to be engineered to create replicon vectors which efficiently induce humoral and T-cell immune responses. They could therefore be used to vaccinate against viral, bacterial, protozoan, and tumor antigens. Gene therapy is the insertion of genes into an individuals cells and tissues to treat a disease, and hereditary diseases in which a defective mutant allele is replaced with a functional one. ... Gene therapy is the insertion of genes into an individuals cells and tissues to treat a disease, and hereditary diseases in which a defective mutant allele is replaced with a functional one. ... A replicon is a DNA molecule or a region of DNA that replicates as an individual unit. ...

See also

• Semliki forest virus
• Sindbis virus
• Chikungunya

The Semliki Forest Virus was first isolated from mosquitoes in the Semliki Forest, Uganda by the Uganda Virus Research Institute in 1944. ... Sindbis Virus (SINV) is a member of the Togaviridae family, in the alphavirus subfamily. ... Chikungunya is a relatively rare form of viral fever caused by an alphavirus that is spread by mosquito bites from Aedes aegypti mosquitoes, though recent research by the Pasteur Institute in Paris claims the virus has suffered a mutation that enables it to be transmitted by Aedes albopictus (Tiger mosquito). ...

Sources

• http://virology-online.com/viruses/Arboviruses2.htm
• http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/73010000.htm
• Alphavirus vectors: from protein production to gene therapy, C Smerdou & P Liljestrom, Gene Therapy and Regulation Vol 1 No 1 2000 pp. 33-63
• Alphavirus vectors and vaccination, J O Rayner et al, Reviews in Medical Virology vol 12 issue 5 pp 279-296
• http://ep.physoc.org/cgi/content/full/90/1/45
• http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.chapter.2894
• http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.2918