West Nile VirusWest Nile Virus

SynopsisSymptomsTransmissionHistoryGeographic distributionTreatmentControl

SynopsisSynopsis

West Nile Virus (or WNV) is a virus of the family Flaviviridae. Part of the Japanese encephalitis (JE) antigenic complex of viruses, it is found in both tropical and temperate regions.

SynopsisSynopsis

It mainly infects birds, but is known to infect humans, horses, dogs, cats, bats, alligators, squirrels, domestic rabbits, chipmunks, and skunks. The main route of human infection is through the bite of an infected mosquito.

chipmunk  Any of several small, striped, terrestrial squirrels of the genera Tamias and Eutamias, especially T. striatus of eastern North America. 花鼠：几种美洲花鼠属和花鼠属的有条纹的陆生小松鼠，尤指北美洲东部的金花鼠红松鼠。skunk  Any of several small, mostly carnivorous New World mammals of the genus Mephitis and related genera, having a bushy tail and black fur with white markings and ejecting a foul-smelling oily liquid from glands near the anus when frightened or in danger. 臭鼬：一种体形小，大部分食肉的东半球臭鼬属及相关种属的哺乳动物，生有浓密的尾巴和带有白色斑点的黑毛，在受惊或遇到危险时从肛门附近的生殖器中射出一种恶臭的油状液体。

SynopsisSynopsis

Image reconstructions and cryoelectron microscopy reveal a 45–50 nm virion covered with a relatively smooth protein surface. This structure is similar to the dengue fever virus; both belong to the genus Flavivirus within the family Flaviviridae.

SynopsisSynopsis

The genetic material of WNV is a positive-sense, single strand of RNA, which is between 11,000 and 12,000 nucleotides long; these genes encode seven non-structural proteins and three structural proteins. The RNA strand is held within a nucleocapsid formed from 12 kDa protein blocks; the capsid is contained within a host-derived membrane altered by two viral glycoproteins.

SymptomsSymptoms

West Nile Virus (WNV) has three different effects on humans.

The first is an asymptomatic infection; The second is a mild febrile syndrome

termed West Nile Fever; The third is a neuroinvasive disease termed

West Nile meningitis or encephalitis. In many infected individuals the ratio

between the three states is roughly 110:30:1.

Transmission Transmission

The virus is transmitted through mosquito vectors, which bite and infect birds. The birds are amplifying hosts, developing sufficient viral levels to transmit the infection to other biting mosquitoes which go on to infect other birds and also humans.

Transmission Transmission

In mammals the virus does not multiply as readily (i.e. does not develop high viremia during infection), and it is believed that mosquitoes biting infected mammals do not ingest sufficient virus to become infected, making mammals so-called dead-end infections.

TransmissionTransmission

The proboscis of an Aedes albopictus mosquito feeding on human blood. Under experimental conditions, the Aedes albopictus mosquito (also known as the Asian Tiger Mosquito) has been found to be a vector of West Nile Virus.

TransmissionTransmission

Although people are most likely to become infected by West Nile Virus through mosquito bites, the virus can also be spread through blood transfusions, organ transplants, breast milk, and from a pregnant woman to her unborn child.

HistoryHistory

Studies of phylogenetic lineages have determined that WNV emerged as a distinct virus around 1000 years ago.

WNV has been posited as one of the possible causes of Alexander the Great's early death based on reports of avian deaths before his illness period.

HistoryHistory

WNV was first isolated from a feverish 37 year old woman at Omogo in the West Nile District of Uganda in 1937 during research on yellow fever virus. It was subsequently identified in Egypt (1942) and India (1953), a 1950 serosurvey in Egypt found 90% of those over 40 years in age had WNV antibodies. The ecology was characterized in 1953 with studies in Egypt and Israel.

HistoryHistory

The virus became recognized as a cause of severe human meningoencephalitis in elderly patients during an outbreak in Israel in 1957. The disease was first noted in horses in Egypt and France in the early 1960s and found to be widespread in southern Europe, southwest Asia and Australia.

HistoryHistory

The first appearance of West Nile virus in the Western hemisphere was in 1999 with encephalitis reported in humans, dogs, cats, and horses, and the subsequent spread in the United States may be an important milestone in the evolving history of this virus.

Cases DeathsMortality Rate

ofreported cases

1999 62 7 11%

2000 21 2 10%

2001 66 10 15%

2002 4156 284 7%

2003 9862 264 3%

2004 2539 100 4%

2005 3000 119 4%

2006 4269 177 4%

2007 3623 124 3%

2008 1356 44 3%

Progress of the West Nile Virus in the United States

62 21 66

4156

9862

25393000

4269

3623

1356

7 210

284

264

100

119

177

124

44

0

2000

4000

6000

8000

10000

12000

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

0

50

100

150

200

250

300

Cases Deaths

0%

20%

40%

60%

80%

100%

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

States are colored according to the percentage of all U.S. West Nile Virus cases they represented in that year. Zero percent (no cases) is colored white; less than 1% is blue; between 1% and 5% is green; between 5% and 10% is yellow, and greater than 10% of cases in a year is red.

This map reflects surveillance findings occurring between January 1, 2008 through December 31, 2008 as reported to CDC's ArboNET system for public distribution by state and local health departments.

Geographic distributionGeographic distribution

Recent outbreaks of West Nile Virus encephalitis in humans have occurred in Algeria (1994), Romania (1996 to 1997), Czech (1997), Congo (1998), Russia (1999), the United States (1999 to 2009), Canada (1999–2003), and Israel (2000).

Epizootics of disease in horses occurred in Morocco (1996), Italy (1998), the United States (1999 to 2001), and France (2000). In 2003, West Nile Virus was found in horses in Mexico.

TreatmentTreatment

There is no treatment for West Nile Virus itself, but infected people receive treatment to alleviate symptoms.

There is no treatment or vaccine for the virus except to alleviate the symptoms; controlling the mosquitoes that carry the disease is the most effective way to limit its spread.

ControlControl

West Nile control is achieved through mosquito control, by elimination of mosquito breeding sites, larviciding active breeding areas and encouraging personal use of mosquito repellents.

The public is also encouraged to spend less time outdoors, wear long covering clothing, apply bug repellant that contains DEET and ensure that mosquitoes cannot enter buildings.

脑脊髓膜炎 [meningitis]由身体其他部位的细菌 ( 包括脑膜炎球菌在内 ) 传染所造成的最严重的感染形式。发病迅速，其症状为呕吐，继之以剧烈头痛及颈强直 ( 通常头向后仰 ) ，幼儿可能出现惊厥。病患者可能在数小时内死亡。脑脊液脓会阻塞脑室与脊柱空间，造成威胁生命的脑积水。用腰椎穿刺迅速做出诊断配合抗生素治疗，可避免脑部伤害和死亡。病毒性脑脊髓膜炎，病程短，通常可自愈。

脑炎 [encephalitis]脑部的炎症，最常见的原因为病毒感染。一类脑炎 ( 包括多发性硬化 ) ，损害隔离神经纤维而非神经元本身的髓鞘。多数类型脑炎的共同症状为发热、头痛、困倦、昏睡、昏迷。惊厥在婴儿多见。典型的神经体征包括动作失调，不随意动作，局部乏力。症状及腰椎穿刺 ( 取脑脊髓液进行分析 ) 可确定诊断，但不能查明病因。一般只作对症治疗及让患者充分安静休息，在复原后仍可能出现各种症状。

DEET(N,N-Diethyl-meta-toluamide)A colorless, oily liquid, C12H17NO, that has a mild odor and is used as an insect repellent. 避蚊胺：一种无色的油状液体， C12H17NO，气味清淡，用以驱虫。

Republic of Uganda Republic of Uganda

Capital

(and largest city)Kampala

Official languages English, Swahili

Area

Total 236,040 km2

Water (%) 15.39

Population

2009 estimate 32,710,000

2002 census 24,227,297

Density 138.5/km2

Republic of UgandaRepublic of Uganda

Ugandan Kob (Kobus kob)

Grey Crowned Crane (Balearica regulorum)