The Western equine encephalomyelitis virus is the causative agent of relatively uncommon viral disease ''Western equine encephalomyelitis'' (WEE). An alphavirus of the family '' Togaviridae'', the WEE virus is an arbovirus (arthropod-borne virus) transmitted by mosquitoes of the genera '' Culex'' and '' Culiseta''. WEE is a recombinant virus between two other alphaviruses, an ancestral Sindbis virus-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 ''Culex tarsalis'', also known as Western Encephalitis Mosquito, is a mosquito species that appears in southern California. The species has black and white banding on the legs. The species is a major vector of Saint Louis encephalitis and West ...

'' and ''

Aedes taeniorhynchus ''Aedes taeniorhynchus'', or the black salt marsh mosquito, is a mosquito in the family Culicidae. It is a carrier for encephalitic viruses including Venezuelan equine encephalitis and can transmit ''Dirofilaria immitis''. It resides in the Ame ...

'') 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 List of longest rivers of the United States (by main stem), second-longest river and chief river of the second-largest Drainage system (geomorphology), drainage system in North America, second only to the Hudson B ...

. 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 sou ...

. 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 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 The Great Depression (19291939) was an economic shock that impacted most countries across the world. It was a period of economic depression that became evident after a major fall in stock prices in the United States. The economic contagio ...

, 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) conditio ...

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 Middlebury College is a private liberal arts college in Middlebury, Vermont. Founded in 1800 by Congregationalists, Middlebury was the first operating college or university in Vermont. The college currently enrolls 2,858 undergraduates from all 5 ...

, 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