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'''Genus ''Alphavirus'''''
'''Genus ''Alphavirus'''''
Single-stranded, linear, positive-sense RNA viruses, 60-70nm in diameter.<ref name="Bertone, J.J (2010) Viral Encephalitis in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12" />
Single-stranded, linear, positive-sense RNA viruses, 60-70nm in diameter.<ref>Bertone, J.J (2010) Viral Encephalitis in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12</ref>[[Image:Alphavirus.gif|300px|thumb|right|''' (Surface of an Alphavirus. This image is a computer-generated model of the surface of an alphavirus derived by cryoelectron microscopy. The spike-like structures on the virion surface are trimers composed of heterodimers of the virion surface glycoproteins E1 and E2. These spikes are used by the virus to attach to susceptible animal cells. ''Sourced from Wikimedia Commons, Copyright of the Centers for Disease Control and Prevention (CDC) Division of Vector-Borne Infectious Diseases, 2007)'' ''']]
[[Image:Alphavirus.gif|300px|thumb|right|''' (Surface of an Alphavirus. This image is a computer-generated model of the surface of an alphavirus derived by cryoelectron microscopy. The spike-like structures on the virion surface are trimers composed of heterodimers of the virion surface glycoproteins E1 and E2. These spikes are used by the virus to attach to susceptible animal cells. ''Sourced from Wikimedia Commons, Copyright of the Centers for Disease Control and Prevention (CDC) Division of Vector-Borne Infectious Diseases, 2007)'' ''']]
===Important Serotypes===
===Important Serotypes===
*Eastern Equine Encephalitis virus (EEV)
*Eastern Equine Encephalitis virus (EEV)
*Western EEV
*Western EEV
*Venezuelan EEV.<ref>Bertone, J.J (2010) Viral Encephalitis in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12</ref>
*Venezuelan EEV.<ref name="Bertone, J.J (2010) Viral Encephalitis in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), ''Saunders'', Chapter 12" />
Eastern EEV has North and South American antigenic variants. Western EEV is a recombinant between an Eastern EEV-like virus and a Sindbis-like virus. Western EEV also has two antigenic subtypes - WEE and Highlands J viruses. Considerable overlap exists between the various strains in terms of their geography, and potentially also in their antigenic properties and biological behaviour. Of the 6 subtypes of Venezuelan EEV (I-VI), significant outbreaks of equine encephalitis in the Western Hemisphere over the last two decades have been caused by IAB, IC and IE. Variant ID from Central America and variant IF from Brazil are considered endemic and typically demonstrate low pathogenicity for horses. These features are also typical of subtype II (Everglades) virus in Florida and types II, IV, V ad VI viruses.
Eastern EEV has North and South American antigenic variants. Western EEV is a recombinant between an Eastern EEV-like virus and a Sindbis-like virus. Western EEV also has two antigenic subtypes - WEE and Highlands J viruses. Considerable overlap exists between the various strains in terms of their geography, and potentially also in their antigenic properties and biological behaviour. Of the 6 subtypes of Venezuelan EEV (I-VI), significant outbreaks of equine encephalitis in the Western Hemisphere over the last two decades have been caused by IAB, IC and IE. Variant ID from Central America and variant IF from Brazil are considered endemic and typically demonstrate low pathogenicity for horses. These features are also typical of subtype II (Everglades) virus in Florida and types II, IV, V ad VI viruses.