The Western equine encephalomyelitis virus is the causative agent of relatively uncommon viral disease ''Western equine encephalomyelitis'' (WEE). An

alphavirus ''Alphavirus'' is a genus of RNA viruses, the sole genus in the ''Togaviridae'' family. Alphaviruses belong to group IV of the Baltimore classification of viruses, with a positive-sense, single-stranded RNA genome. There are 32 alphaviruses ...

of the family ''

Togaviridae This category is for articles about virus families (or redirects to such articles). There should be no subcategories. families Families (biology) ...

'', the WEE virus is an

arbovirus Arbovirus is an informal name for any virus that is transmitted by arthropod vectors. The term ''arbovirus'' is a portmanteau word (''ar''thropod-''bo''rne ''virus''). ''Tibovirus'' (''ti''ck-''bo''rne ''virus'') is sometimes used to more sp ...

(arthropod-borne virus) transmitted by

mosquitoes Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small Diptera, flies within the family Culicidae (from the Latin ''culex'' meaning "gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish ...

of the genera ''

Culex ''Culex'' is a genus of mosquitoes, several species of which serve as vectors of one or more important diseases of birds, humans, and other animals. The diseases they vector include arbovirus infections such as West Nile virus, Japanese encep ...

'' and '' Culiseta''. WEE is a

recombinant virus A recombinant virus may occur naturally or be produced by recombining pieces of DNA using recombinant DNA technology. Synthetic recombination This may be used to produce viral vaccines or gene therapy vectors. Natural recombination The term ...

between two other alphaviruses, an ancestral

Sindbis virus ''Sindbis virus'' (SINV) is a member of the ''Togaviridae'' family, in the ''Alphavirus'' genus. The virus was first isolated in 1952 in Cairo, Egypt. The virus is transmitted by mosquitoes (''Culex'' and Culiseta). SINV is linked to Pogosta di ...

-like virus, and an ancestral Eastern equine encephalitis virus-like virus. There have been under 700 confirmed cases in the U.S. since 1964. This virus contains an envelope that is made up of glycoproteins and nucleic acids. The virus is transmitted to people and horses by bites from infected mosquitoes ('' Culex tarsalis'' and '' Aedes taeniorhynchus'') and birds during wet, summer months. According to the CDC, geographic occurrence for this virus is worldwide, and tends to be more prevalent in places in and around swampy areas where human populations tend to be limited. In the U.S., WEE is seen primarily in states and Canadian provinces west of the

Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it fl ...

. The disease is also seen in countries of

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

. WEE is commonly a subclinical infection; symptomatic infections are uncommon. However, the disease can cause serious sequelae in infants and children. Unlike Eastern equine encephalitis, the overall mortality of WEE is low (approximately 4%) and is associated mostly with infection in the elderly. Approximately 15–20% of horses that acquire the virus will die or be put down. There is no human vaccine for WEE and there are no licensed therapeutic drugs in the U.S. for this infection. The virus affects the brain and spinal cord of the infected host.

History

WEE was discovered in 1930 when a number of

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million yea ...

s in the

San Joaquin Valley The San Joaquin Valley ( ; es, Valle de San Joaquín) is the area of the Central Valley of the U.S. state of California that lies south of the Sacramento–San Joaquin River Delta and is drained by the San Joaquin River. It comprises seven ...

of California, USA died of a mysterious encephalitis. Karl Friedrich Meyer investigated but was not able to isolate the pathogen from

necropsies An autopsy (post-mortem examination, obduction, necropsy, or autopsia cadaverum) is a surgical procedure that consists of a thorough examination of a corpse by dissection to determine the cause, mode, and manner of death or to evaluate any di ...

of horses that had been dead for some time and needed samples from an animal in the earlier stages of disease. When the team heard of a horse that appeared to have encephalitis, its owner threatened to shoot the scientists. However Meyer was able to convince the farmer's wife that the horse was dying anyway, and to secretly signal him when the farmer was asleep in exchange for $20 (as this was during the Great Depression, this was a substantial amount of money). Meyer and his colleagues hid in the bushes until the signal,

euthanized Animal euthanasia ( euthanasia from el, εὐθανασία; "good death") is the act of killing an animal or allowing it to die by withholding extreme medical measures. Reasons for euthanasia include incurable (and especially painful) conditi ...

the horse and stole its head. They successfully isolated WEEV from the brain tissue.

Biological weapon

Western equine encephalitis virus was one of more than a dozen agents that the United States researched as potential biological weapons before the nation suspended its biological weapons program.Chemical and Biological Weapons: Possession and Programs Past and Present
, ''James Martin Center for Nonproliferation Studies'', Middlebury College, April 9, 2002, accessed 31 March 2010.

References

External links

United States Centers for Disease Control and Prevention (CDC) Fact Sheet
{{Taxonbar, from=Q324467 Animal viral diseases Biological weapons Viral encephalitis Bird diseases Parasites of birds Horse diseases Alphaviruses Insect-borne diseases

History

Biological weapon

See also

References

External links