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[[Equine Togaviral Encephalitis]]
[[Equine Togaviral Encephalitis]]
====Epizootiology====
====Distribution====
Virus distribution is largely dictated by the distribution of appropriate vectors. Thus Eastern EEV can be found in a region extending from eastern Canada at its northern extremity, down throughout the Caribbean and in parts of Central and South America. The virus has also been identifed in the Philippines and may be present in Europe. Over the last two decades, Western EEV has rarely caused disease in the western United States, although it is found here in avian reservoir hosts. As well as producing disease outbreaks in Mexico, Venezuela and colombia, Venezuelan EEV has recently been recognized in Peru, Brazil, French Guiana and Trinidad.
=====Distribution=====
=====Reservoirs=====
Togaviridae survive by asymptomatically infecting sylvatic hosts such as birds, small mammals, reptiles and amphibians. Overwintering occurs in these wild populations.
=====Vectors=====
=====Vectors=====
The major disease vectors for each serotype of veterinary significance are:
The most significant disease vectors for each serotype are:
*EEE: ''Aedes'' spp.
*Eastern EEV: ''Aedes'' spp.
*WEE: ''Culex tarsalis''
*Western EEV: ''Culex tarsalis''
*VEE: ''Culex melanconium'', ''Aedes'' spp., ''Phosphora'' spp.
*Venezuelan EEV: ''Culex melanconium'', ''Aedes'' spp., ''Phosphora'' spp.
''Culiseta melanura'' is a vector for EEE. It is largely confined to freshwater swamps, feeds primarily on swamp birds and is rarely found in areas of increased horse density. This mosquito generally serves as a vector for the enzootic cycle involving swamp birds. ''Aedes'' spp. are more important in epizootics and epidemics. Culex tarsalis is the primary vector that maintains WEE virus in an enzootic cycle with passerine birds. Dermacentor andersoni ticks, Triatoma sanguisuga (assassin bug), and the cliff swallow bug (Oeciacus vicarius) may also be involved as vectors or overwintering reservoirs fro WEE. Several species of mosquitoes from at least 11 geerna have been determined ot be naturally infected with epidemic strains of VEE virus. Ticks may also be capable of viral trasnmission.
''Culiseta melanura'' is a vector for EEE. It is largely confined to freshwater swamps, feeds primarily on swamp birds and is rarely found in areas of increased horse density. This mosquito generally serves as a vector for the enzootic cycle involving swamp birds. ''Aedes'' spp. are more important in epizootics and epidemics. Culex tarsalis is the primary vector that maintains WEE virus in an enzootic cycle with passerine birds. Dermacentor andersoni ticks, Triatoma sanguisuga (assassin bug), and the cliff swallow bug (Oeciacus vicarius) may also be involved as vectors or overwintering reservoirs fro WEE. Several species of mosquitoes from at least 11 geerna have been determined ot be naturally infected with epidemic strains of VEE virus. Ticks may also be capable of viral trasnmission.
Vectors transmit viral particles between sylvatic hosts when takin ga blood meal. If the virus can peentrate the gut of the vector, then it may pass throhg the haemolymph to the oral glands, multiply and subsequntrly be shed in the saliva and other oral secretions. If th eblood meal octnains adequate numbers of viral particles, multiplication may not be rrequired for transmission. It is likely tha the mosquito remians infected for life.
Vectors transmit viral particles between sylvatic hosts when takin ga blood meal. If the virus can peentrate the gut of the vector, then it may pass throhg the haemolymph to the oral glands, multiply and subsequntrly be shed in the saliva and other oral secretions. If th eblood meal octnains adequate numbers of viral particles, multiplication may not be rrequired for transmission. It is likely tha the mosquito remians infected for life.