Editing West Nile fever

{{Short description|Human disease caused by West Nile virus infection}}
{{Cleanup image captions|date=March 2025|succinct=too many of the captions in this article are long paragraphs; content needs to be moved into the article body and the captions shortened}}
{{About|the disease|the virus|West Nile virus}}
{{Infobox medical condition (new)
| name            = West Nile fever
| image           = Em wnvirus j7908i.jpg
| caption         = West Nile virus
| field           = [[Infectious disease (medical specialty)|Infectious disease]]
| symptoms        = None, [[fever]], headache, vomiting or diarrhea and muscle aches rash<ref name=CDC2017Q/>
| complications   = [[Encephalitis]], [[meningitis]]<ref name=CDC2017Q/>
| onset           = 2 to 14 days after exposure<ref name=CDC2017Q/>
| duration        = Weeks to months<ref name=CDC2017Q/>
| types           =
| causes          = West Nile virus spread by [[mosquito]]<ref name=CDC2017Q/>
| risks           = Infants, elderly, [[immunodeficiency|weak immune system]]<ref name=Jong2022>{{cite book |first=Johnie A.|last=Yates|editor1-last=Jong |editor1-first=Elaine C. |editor2-last=Stevens |editor2-first=Dennis L. |title=Netter's Infectious Diseases |date=2022 |publisher=Elsevier |location=Philadelphia |isbn=978-0-323-71159-3 |page=419|edition=2nd |chapter-url=https://books.google.com/books?id=l8skEAAAQBAJ&pg=PA419|language=en |chapter=70. Arboviruses of medical importance}}</ref>
| diagnosis       = Based on symptoms and blood tests<ref name=CDC2017Q/>
| differential    =
| prevention      = Reducing mosquitoes, preventing mosquito bites<ref name=CDC2017Q/>
| treatment       = [[Supportive care]] (pain medication)<ref name=CDC2017Q/>
| medication      =
| prognosis       = 10% risk of death among those seriously affected<ref name=CDC2017Q/>
| frequency       =
| deaths          =
}}

'''West Nile fever''' is an infection by the [[West Nile virus]], which is typically spread by [[mosquito]]es.<ref name=CDC2017Q>{{cite web |title=General Questions About West Nile Virus |url=https://www.cdc.gov/westnile/faq/genQuestions.html |website=www.cdc.gov |access-date=26 October 2017 |language=en-us |date=19 October 2017 |url-status=live |archive-url=https://web.archive.org/web/20171026111330/https://www.cdc.gov/westnile/faq/genQuestions.html |archive-date=26 October 2017 }}</ref> In about 80% of infections people have [[Subclinical infection|few]] or [[Asymptomatic|no symptoms]].<ref name=CDC2019Sym>{{cite web |title=Symptoms, Diagnosis, & Treatment |url=https://www.cdc.gov/westnile/symptoms/index.html |website=www.cdc.gov |access-date=15 January 2019 |language=en-us |date=15 January 2019 |url-status=live |archive-url=https://web.archive.org/web/20171026111330/https://www.cdc.gov/westnile/symptoms/index.html |archive-date=26 October 2017 }}</ref> About 20% of people develop a [[fever]], headache, vomiting, or a rash.<ref name=CDC2017Q/> In less than 1% of people, [[encephalitis]] or [[meningitis]] occurs, with associated neck stiffness, confusion, or seizures.<ref name=CDC2017Q/> Recovery may take weeks to months.<ref name=CDC2017Q/> The risk of death among those in whom the [[nervous system]] is affected is about 10 percent.<ref name=CDC2017Q/>

West Nile virus (WNV) is usually spread by mosquitoes that become infected when they feed on infected birds, which [[natural host|often carry the disease]].<ref name=CDC2017Q/> Rarely the virus is spread through blood transfusions, organ transplants, or from mother to baby during pregnancy, delivery, or breastfeeding,<ref name=CDC2017Q/> but it otherwise does not spread directly between people.<ref name=WHO2011/> Risks for severe disease include being over 60 years old and having other health problems.<ref name=CDC2017Q/> Diagnosis is typically based on symptoms and blood tests.<ref name=CDC2017Q/>

There is no human [[vaccine]].<ref name=CDC2017Q/> The best way to reduce the risk of infection is to avoid mosquito bites.<ref name=CDC2017Q/> Mosquito populations may be reduced by eliminating standing pools of water, such as in old tires, buckets, gutters, and swimming pools.<ref name=CDC2017Q/> When mosquitoes cannot be avoided, [[mosquito repellent]], [[window screen]]s, and [[mosquito nets]] reduce the likelihood of being bitten.<ref name=CDC2017Q/><ref name=WHO2011/> There is no specific treatment for the disease; [[pain medications]] may reduce symptoms.<ref name=CDC2017Q/>

The virus was discovered in [[Uganda]] in 1937, and was first detected in North America in 1999.<ref name=CDC2017Q/><ref name=WHO2011/> WNV has occurred in Europe, Africa, Asia, Australia, and North America.<ref name=CDC2017Q/> In the United States thousands of cases are reported a year, with most occurring in August and September.<ref>{{cite web|title=Final Cumulative Maps and Data {{!}} West Nile Virus {{!}} CDC|url=https://www.cdc.gov/westnile/statsmaps/cumMapsData.html |website=www.cdc.gov|access-date=28 October 2017|language=en-us|date=24 October 2017 |url-status=live |archive-url=https://web.archive.org/web/20171027180705/https://www.cdc.gov/westnile/statsmaps/cumMapsData.html |archive-date=27 October 2017 }}</ref> It can occur in outbreaks of disease.<ref name=WHO2011/> Severe disease may also occur in horses, for which a vaccine is available.<ref name=WHO2011>{{cite web |title=West Nile virus |url=https://www.who.int/mediacentre/factsheets/fs354/en/ |website=World Health Organization |access-date=28 October 2017 |date=July 2011 |url-status=live |archive-url=https://web.archive.org/web/20171018044431/http://www.who.int/mediacentre/factsheets/fs354/en/ |archive-date=18 October 2017 }}</ref> A surveillance system in birds is useful for early detection of a potential human outbreak.<ref name=WHO2011/>
{{TOC limit}}

==Signs and symptoms==
About 80% of those infected with [[West Nile virus]] (WNV) show [[asymptomatic|no symptoms]] and go unreported.<ref>{{cite web |last1=Gompf |first1=Sandra |title=West Nile Virus |url=https://www.medicinenet.com/west_nile_encephalitis/article.htm |website=Medicine Net |publisher=MedicineNet Inc. |access-date=15 January 2019}}</ref> About 20% of infected people develop symptoms. These vary in severity, and begin 3 to 14 days after being bitten. Most people with mild symptoms of WNV recover completely, though fatigue and weakness may last for weeks or months. Symptoms may range from mild, such as [[fever]], to severe, such as [[paralysis]] and [[meningitis]]. A severe infection can last weeks and can, rarely, cause [[permanent brain damage]]. [[Death]] may ensue if the central nervous system is affected. Medical conditions such as [[cancer]] and [[diabetes]], and age over 60 years, increase the risk of developing severe symptoms.<ref>{{cite web |title=Symptoms, Diagnosis, & Treatment |url=https://www.cdc.gov/westnile/symptoms/index.html |website=Centers for Disease Control and Prevention |publisher=USA.gov |access-date=15 January 2019|date=2018-12-10 }}</ref><ref>{{cite web |title=West Nile virus |url=https://www.mayoclinic.org/diseases-conditions/west-nile-virus/diagnosis-treatment/drc-20350325 |website=Mayoclinic |publisher=Mayo Foundation for Medical Education and Research (MFMER) |access-date=15 January 2019}}</ref>

Headache can be a prominent symptom of WNV fever, meningitis, encephalitis, meningoencephalitis, and it may or may not be present in poliomyelitis-like syndrome. Thus, headache is not a useful indicator of neuroinvasive disease.
* West Nile fever (WNF), which occurs in 20 percent of cases, is a [[fever|febrile]] [[syndrome]] that causes [[flu-like symptoms]].<ref>{{cite journal |author=Olejnik E |title=Infectious adenitis transmitted by ''Culex molestus'' |journal=Bull Res Counc Isr |volume=2 |pages=210–1 |year=1952}}</ref> Most characterizations of WNF describe it as a mild, [[acute (medicine)|acute]] syndrome lasting 3 to 6 days after symptom onset. Systematic follow-up studies of patients with WNF have not been done, so this information is largely [[Anecdotal evidence|anecdotal]]. Possible symptoms include high fever, headache, chills, [[diaphoresis|excessive sweating]], weakness, fatigue, [[lymphadenopathy|swollen lymph nodes]], drowsiness, pain in the joints and [[flu-like symptoms]]. There may be [[Human gastrointestinal tract|gastrointestinal]] symptoms including [[nausea]], [[emesis|vomiting]], [[Anorexia (symptom)|loss of appetite]], and [[diarrhea]]. Fewer than one-third of patients develop a [[rash]].
* West Nile [[Neurotropic virus|neuroinvasive disease]] (WNND), which occurs in less than 1 percent of cases, is when the virus infects the [[central nervous system]] resulting in [[meningitis]], [[encephalitis]], meningoencephalitis or a [[poliomyelitis]]-like syndrome.<ref name="Davis2006">{{cite journal |vauthors=Davis LE, DeBiasi R, Goade DE, etal |date=Sep 2006 |title=West Nile virus neuroinvasive disease |journal=[[Annals of Neurology]] |volume=60 |issue=3 | pages=286–300 |pmid=16983682 |doi=10.1002/ana.20959|s2cid=30778922 }}</ref> Many patients with WNND have normal [[neuroimaging]] studies, although abnormalities may be present in various cerebral areas including the [[basal ganglia]], [[thalamus]], [[cerebellum]], and [[brainstem]].<ref name="Davis2006" />
* West Nile virus encephalitis (WNE) is the most common neuroinvasive manifestation of WNND. WNE presents with similar symptoms to other viral encephalitis with fever, headaches, and altered mental status. A prominent finding in WNE is [[muscular weakness]] (30 to 50 percent of patients with encephalitis), often with [[lower motor neuron]] symptoms, [[flaccid paralysis]], and [[hyporeflexia]] with no [[Sensory system|sensory]] abnormalities.<ref>{{cite journal |vauthors=Flores Anticona EM, Zainah H, Ouellette DR, Johnson LE |title=Two case reports of neuroinvasive west nile virus infection in the critical care unit |journal=Case Reports in Infectious Diseases |volume=2012 |pages=1–4 |year=2012 |pmid=22966470 |pmc=3433121 |doi=10.1155/2012/839458|doi-access=free }}</ref><ref name=Carson06>{{cite journal |vauthors=Carson PJ, Konewko P, Wold KS, etal |title=Long-term clinical and neuropsychological outcomes of West Nile virus infection |journal=[[Clinical Infectious Diseases]] |volume=43 |issue=6 |pages=723–30 |year=2006 |pmid=16912946 |doi=10.1086/506939 |s2cid=2765866 |url=https://academic.oup.com/cid/article-pdf/43/6/723/933835/43-6-723.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://academic.oup.com/cid/article-pdf/43/6/723/933835/43-6-723.pdf |archive-date=2022-10-09 |url-status=live}}</ref>
* West Nile meningitis (WNM) usually involves fever, headache, stiff neck and [[pleocytosis]], an increase of white blood cells in cerebrospinal fluid. Changes in consciousness are not usually seen and are mild when present.
* West Nile meningoencephalitis is inflammation of both the brain (encephalitis) and meninges (meningitis).
* West Nile poliomyelitis (WNP), an [[acute flaccid paralysis]] syndrome associated with WNV infection, is less common than WNM or WNE. This syndrome is generally characterized by the acute onset of asymmetric limb weakness or paralysis in the absence of sensory loss. Pain sometimes precedes the paralysis. The paralysis can occur in the absence of fever, headache, or other common symptoms associated with WNV infection. Involvement of respiratory muscles, leading to acute respiratory failure, sometimes occurs.
* West-Nile reversible paralysis, Like WNP, the weakness or paralysis is asymmetric.<ref name="Mojumder2014">{{cite journal |author=Mojumder, D.K., Agosto, M., Wilms, H. |date=March 2014 |title=Is initial preservation of deep tendon reflexes in West Nile Virus paralysis a good prognostic sign? |journal=Neurology Asia |volume=19 |issue=1 |pages=93–97 |display-authors=etal |pmid=25400704 |pmc=4229851}}</ref> Reported cases have been noted to have an initial preservation of deep tendon reflexes, which is not expected for a pure anterior horn involvement.<ref name="Mojumder2014"/> Disconnect of upper motor neuron influences on the anterior horn cells possibly by myelitis or glutamate excitotoxicity have been suggested as mechanisms.<ref name="Mojumder2014"/> The prognosis for recovery is excellent.
* Nonneurologic complications of WNV infection that may rarely occur include fulminant [[hepatitis]], [[pancreatitis]],<ref>{{cite journal |vauthors=Asnis DS, Conetta R, Teixeira AA, Waldman G, Sampson BA |title=The West Nile Virus outbreak of 1999 in New York: the Flushing Hospital experience |journal=Clinical Infectious Diseases |volume=30 |issue=3 |pages=413–8 |date=March 2000 |pmid=10722421 |doi=10.1086/313737|doi-access=free }}</ref> [[myocarditis]], [[rhabdomyolysis]],<ref>{{cite journal |vauthors=Montgomery SP, Chow CC, Smith SW, Marfin AA, O'Leary DR, Campbell GL |title=Rhabdomyolysis in patients with west nile encephalitis and meningitis |journal=Vector-Borne and Zoonotic Diseases |volume=5 |issue=3 |pages=252–7 |year=2005 |pmid=16187894 |doi=10.1089/vbz.2005.5.252|s2cid=33442661 }}</ref> [[orchitis]],<ref>{{cite journal |vauthors=Smith RD, Konoplev S, DeCourten-Myers G, Brown T |title=West Nile virus encephalitis with myositis and orchitis |journal=Hum. Pathol. |volume=35 |issue=2 |pages=254–8 |date=February 2004 |pmid=14991545 |doi=10.1016/j.humpath.2003.09.007 }}</ref> [[nephritis]], [[optic neuritis]]<ref>{{cite journal |vauthors=Anninger WV, Lomeo MD, Dingle J, Epstein AD, Lubow M |title=West Nile virus-associated optic neuritis and chorioretinitis |journal=Am. J. Ophthalmol. |volume=136 |issue=6 |pages=1183–5 |year=2003|pmid=14644244 |doi=10.1016/S0002-9394(03)00738-4}}</ref> and [[cardiac dysrhythmia]]s and [[hemorrhagic fever]] with [[coagulopathy]].<ref>{{cite journal |vauthors=Paddock CD, Nicholson WL, Bhatnagar J, etal |title=Fatal hemorrhagic fever caused by West Nile virus in the United States |journal=Clinical Infectious Diseases |volume=42 |issue=11 |pages=1527–35 |date=June 2006 |pmid=16652309 |doi=10.1086/503841|doi-access= }}</ref> [[Chorioretinitis]] may also be more common than previously thought.<ref>{{cite journal |vauthors=Shaikh S, Trese MT |title=West Nile virus chorioretinitis |journal=Br J Ophthalmol |volume=88 |issue=12 |pages=1599–60 |year=2004 |pmid=15548822 |pmc=1772450 |doi=10.1136/bjo.2004.049460}}</ref>
* Skin manifestations, specifically rashes, are common; however, there are few detailed descriptions in case reports, and few images are available. Punctate erythematous, macular, and papular eruptions, most pronounced on the extremities have been observed in WNV cases and in some cases histopathologic findings have shown a sparse superficial [[Pericyte|perivascular]] lymphocytic infiltrate, a manifestation commonly seen in viral exanthems. A literature review provides support that this punctate rash is a common cutaneous presentation of WNV infection.<ref>{{cite journal |vauthors=Anderson RC, Horn KB, Hoang MP, Gottlieb E, Bennin B |title=Punctate exanthem of West Nile Virus infection: report of 3 cases |journal=J. Am. Acad. Dermatol. |volume=51 |issue=5 |pages=820–3 |date=November 2004 |pmid=15523368 |doi=10.1016/j.jaad.2004.05.031}}</ref>

==Cause==
===Virology===
{{Main|West Nile virus}}
[[File:WNV life cycle.jpg|right|thumb|West Nile virus life cycle. After binding and uptake, the virion envelope fuses with cellular membranes, followed by uncoating of the nucleocapsid and release of the RNA genome into the cytoplasm. The viral genome serves as messenger RNA (mRNA) for translation of all viral proteins and as template during RNA replication. Copies are subsequently packaged within new virus particles that are transported in vesicles to the cell membrane.]]
WNV is one of the [[Japanese encephalitis]] antigenic [[Serotype|serocomplex]] of viruses.<ref>{{cite journal | pmc=3337329 | pmid=22309667 | doi=10.1586/erv.11.180 | volume=11 | issue=2 | title=Feasibility of cross-protective vaccination against flaviviruses of the Japanese encephalitis serocomplex | year=2012 | journal=Expert Rev Vaccines | pages=177–87 |vauthors=Lobigs M, Diamond MS }}</ref>
Image reconstructions and [[cryoelectron microscopy]] reveal a 45–50&nbsp;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]]''. The genetic material of WNV is a [[Sense (molecular biology)|positive-sense]], single strand of [[RNA]], which is between 11,000 and 12,000 [[nucleotide]]s long; these [[genes]] encode seven nonstructural 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 [[Biological membrane|membrane]] altered by two viral membrane proteins.<ref name="auto">{{Cite web |title=Home - PMC - NCBI |url=https://www.ncbi.nlm.nih.gov/pmc/ |access-date=2022-06-24 |website=www.ncbi.nlm.nih.gov}}</ref>

West Nile virus has been seen to replicate faster and spread more easily to birds at higher temperatures; one of several ways climate change could affect the epidemiology of this disease.<ref name=Paz2015/>

===Transmission===
[[File:West Nile virus transmission cycle.jpg|thumb|left|West Nile virus maintains itself in nature by cycling between mosquitoes in the genus ''Culex'' and certain species of birds. A mosquito (the [[Vector (epidemiology)|vector]]) bites an uninfected bird (the [[Host (biology)|host]]), the virus amplifies within the bird, an uninfected mosquito bites the bird and is in turn infected. Other species such as humans and horses are incidental infections, because the virus does not amplify well within these species and they are considered dead-end hosts.]]
The prime method of spread of the West Nile virus (WNV) is the female mosquito. In Europe, cats were identified as [[Feline zoonosis|being hosts]] for [[West Nile virus]].<ref name="RijksCito2016">{{cite journal|last1=Rijks|first1=J.M.|last2=Cito|first2=F.|last3=Cunningham|first3=A.A.|last4=Rantsios|first4=A.T.|last5=Giovannini|first5=A.|title=Disease Risk Assessments Involving Companion Animals: an Overview for 15 Selected Pathogens Taking a European Perspective|journal=Journal of Comparative Pathology|volume=155|issue=1|year=2016|pages=S75–S97|issn=0021-9975|doi=10.1016/j.jcpa.2015.08.003|pmid=26422413|doi-access=free}}</ref>
The important mosquito vectors vary according to area; in the United States, ''[[Culex pipiens]]'' (Eastern United States, and urban and residential areas of the United States north of 36–39°N), ''[[Culex tarsalis]]'' (Midwest and West), and ''[[Culex quinquefasciatus]]'' (Southeast) are the main vector species.<ref>{{cite journal |vauthors=Hayes EB, Komar N, Nasci RS, Montgomery SP, O'Leary DR, Campbell GL |title=Epidemiology and transmission dynamics of West Nile virus disease |journal=Emerging Infect. Dis. |volume=11 |issue=8 |pages=1167–73 |year=2005 |pmid=16102302 |doi=10.3201/eid1108.050289a |pmc=3320478 }}</ref> In Europe, ''Culex pipiens'' is the principal vector.<ref>{{Cite journal |last1=Vogels |first1=Chantal Bf |last2=Göertz |first2=Giel P. |last3=Pijlman |first3=Gorben P. |last4=Koenraadt |first4=Constantianus Jm |date=2017-11-08 |title=Vector competence of European mosquitoes for West Nile virus |journal=Emerging Microbes & Infections |volume=6 |issue=11 |pages=e96 |doi=10.1038/emi.2017.82 |issn=2222-1751 |pmc=5717085 |pmid=29116220}}</ref>

The mosquito species that are most frequently infected with WNV feed primarily on birds.<ref name=Kilpatrick_2011>{{cite journal|last=Kilpatrick |first=A.M. |title= Globalization, land use, and the invasion of West Nile virus |journal=Science |year=2011|volume=334|issue=6054 |pages=323–327|pmid= 22021850 |pmc=3346291 |doi= 10.1126/science.1201010|bibcode=2011Sci...334..323K }}</ref> Different species of mosquitos take a [[hematophagy|blood meal]] from different types of [[vertebrate]] [[Host (biology)|host]]s, Mosquitoes show further selectivity, exhibiting preference for different [[species]] of birds. In the United States, WNV mosquito vectors feed preferentially on members of the [[Corvidae]] and [[Thrush (bird)|thrush]] [[Family (biology)|family]]. Among the preferred species within these families are the [[American crow]], a corvid, and the [[American robin]] (''Turdus migratorius'').<ref name="Kilpatrick_2006A">{{cite journal|last=Kilpatrick, AM, P Daszak, MJ Jones, PP Marra, LD Kramer|year=2006|title=Host heterogeneity dominates West Nile virus transmission|journal=Proceedings of the Royal Society B: Biological Sciences|volume=273|issue=1599|pages=2327–2333|doi=10.1098/rspb.2006.3575|pmc=1636093|pmid=16928635}}</ref>

Some species of birds develop sufficient viral levels (>~10<sup>4.2</sup> log PFU/ml;<ref name=Kilpatrick_2007>{{cite journal | last=Kilpatrick, AM, SL LaDeau, PP Marra | title= Ecology of West Nile virus transmission and its impact on birds in the western hemisphere | journal= Auk | volume= 124 | issue= 4 | year=2007 | pages=1121–1136 | doi=10.1642/0004-8038(2007)124[1121:eownvt]2.0.co;2| s2cid= 13796761 | url= https://repository.si.edu/bitstream/handle/10088/35181/NZP_Marra_2007-ECOLOGY_OF_WEST_NILE_VIRUS_TRANSMISSION_AND_ITS_IMPACT_ON_BIRDS_IN_THE_WESTERN_HEMISPHERE.pdf;https://repository.si.edu/bitstream/handle/10088/35181/NZP_Marra_2007-ECOLOGY_OF_WEST_NILE_VIRUS_TRANSMISSION_AND_ITS_IMPACT_ON_BIRDS_IN_THE_WESTERN_HEMISPHERE.pdf | type= Submitted manuscript }}</ref>) after being infected to transmit the infection to biting mosquitoes that in turn go on to infect other birds. In birds that die from WNV, death usually occurs after 4 to 6 days.<ref name=Komar_2003>{{cite journal | last=Komar, N, S Langevin, S Hinten, N Nemeth, E Edwards, D Hettler, B Davis, R Bowen, M Bunning | title= Experimental infection of North American birds with the New York 1999 strain of West Nile virus | journal= Emerging Infectious Diseases | volume= 9 | issue= 3 | year=2003 | pages=311–322 |pmid= 12643825 | pmc= 2958552 | doi=10.3201/eid0903.020628}}</ref>  In mammals and several species of birds, the virus does not multiply as readily and so does not develop high [[viremia]] during infection.  Mosquitoes biting such hosts are not believed to ingest sufficient virus to become infected, making them so-called [[Host (biology)|dead-end hosts]].<ref name=Kilpatrick_2007/>  As a result of the differential infectiousness of hosts, the feeding patterns of mosquitoes play an important role in WNV transmission,<ref name=Kilpatrick_2011/><ref name=Kilpatrick_2006A/> and they are partly genetically controlled, even within a species.<ref>{{Cite journal |last1=Brugman |first1=V. A. |last2=Hernández-Triana |first2=L. M. |last3=England |first3=M. E. |last4=Medlock |first4=J. M. |last5=Mertens |first5=P. P. C. |last6=Logan |first6=J. G. |last7=Wilson |first7=A. J. |last8=Fooks |first8=A. R. |last9=Johnson |first9=N. |last10=Carpenter |first10=S. |date=2017-03-27 |title=Blood-feeding patterns of native mosquitoes and insights into their potential role as pathogen vectors in the Thames estuary region of the United Kingdom |journal=Parasites & Vectors |volume=10 |issue=1 |pages=163 |doi=10.1186/s13071-017-2098-4 |issn=1756-3305 |pmc=5369192 |pmid=28347323 |doi-access=free }}</ref>

Direct human-to-human transmission initially was believed to be caused only by occupational exposure, such as in a laboratory setting,<ref>{{cite journal |title=Laboratory-acquired West Nile virus infections—United States, 2002 |journal=MMWR Morb. Mortal. Wkly. Rep.|volume=51 |issue=50 |pages=1133–5 |year=2002 |pmid=12537288 |author1= Centers for Disease Control and Prevention (CDC)}}</ref> or [[conjunctiva]]l exposure to infected blood.<ref>{{cite journal  |vauthors=Fonseca K, Prince GD, Bratvold J, etal |title=West Nile virus infection and conjunctive exposure |journal=Emerging Infect. Dis. |volume=11|issue=10|pages=1648–9 |year=2005 |pmid=16355512 |doi= 10.3201/eid1110.040212 |pmc=3366727}}</ref> The US outbreak identified additional transmission methods through blood transfusion,<ref>{{cite journal |title=Investigation of blood transfusion recipients with West Nile virus infections |journal=MMWR Morb. Mortal. Wkly. Rep. |volume=51 |issue=36 |pages=823 |year=2002 |pmid=12269472 |author1= Centers for Disease Control and Prevention (CDC)}}</ref> organ transplant,<ref>{{cite journal |title=West Nile virus infection in organ donor and transplant recipients—Georgia and Florida, 2002 |journal=MMWR Morb. Mortal. Wkly. Rep.|volume=51 |issue=35 |pages=790 |year=2002 |pmid=12227442 |author1= Centers for Disease Control and Prevention (CDC)}}</ref> intrauterine exposure,<ref>{{cite journal |title=Intrauterine West Nile virus infection—New York, 2002|journal=MMWR Morb. Mortal. Wkly. Rep. |volume=51 |issue=50 |pages=1135–6 |year=2002 |pmid=12537289 |author1= Centers for Disease Control and Prevention (CDC) }}</ref> and breast feeding.<ref>{{cite journal |title=Possible West Nile virus transmission to an infant through breast-feeding—Michigan, 2002 |journal=MMWR Morb. Mortal. Wkly. Rep. |volume=51|issue=39|pages=877–8 |year=2002 |pmid=12375687 |author1= Centers for Disease Control and Prevention (CDC) }}</ref> Since 2003, blood banks in the United States routinely screen for the virus among their donors.<ref>{{cite journal |title=Detection of West Nile virus in blood donations—United States, 2003 |journal=MMWR Morb. Mortal. Wkly. Rep. |volume=52 |issue=32 |pages=769–72 |year=2003 |pmid=12917583 |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5232a3.htm |author1=Centers for Disease Control and Prevention (CDC) |url-status=live |archive-url=https://web.archive.org/web/20170625121109/https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5232a3.htm |archive-date=2017-06-25 }}</ref> As a precautionary measure, the UK's [[National Blood Service]] initially ran a test for this disease in donors who donate within 28 days of a visit to the United States, Canada, or the northeastern provinces of Italy, and the [[Scottish National Blood Transfusion Service]]<ref>[https://web.archive.org/web/20080820072151/http://www.scotblood.co.uk/westNile.asp West Nile Virus]. Scottish National Blood Transfusion Service.</ref> asks prospective donors to wait 28 days after returning from North America or the northeastern provinces of Italy before donating. There also have been reports of possible transmission of the virus from mother to child during [[pregnancy]] or [[breastfeeding]] or exposure to the virus in a lab, but these are rare cases and not conclusively confirmed.<ref name="Mayo Clinic">{{cite web|title=West Nile virus|url=https://www.mayoclinic.org/diseases-conditions/west-nile-virus/symptoms-causes/syc-20350320|website=Mayo Clinic|access-date=25 October 2017|url-status=live|archive-url=https://web.archive.org/web/20171026001453/https://www.mayoclinic.org/diseases-conditions/west-nile-virus/symptoms-causes/syc-20350320|archive-date=26 October 2017}}</ref>

Recently, the potential for [[Mosquito#Saliva|mosquito saliva]] to affect the course of WNV disease was demonstrated.<ref name="pmid18000543">{{cite journal |author=Schneider BS, McGee CE, Jordan JM, Stevenson HL, Soong L, Higgs S |title=Prior exposure to uninfected mosquitoes enhances mortality in naturally-transmitted West Nile virus infection |journal=PLOS ONE|volume=2 |issue=11 |pages=e1171 |year=2007 |pmid=18000543|doi=10.1371/journal.pone.0001171|pmc=2048662 |editor1-last=Baylis |editor1-first=Matthew|bibcode=2007PLoSO...2.1171S |doi-access=free }}</ref><ref name="pmid16896145">{{cite journal |vauthors=Styer LM, Bernard KA, Kramer LD |title=Enhanced early West Nile virus infection in young chickens infected by mosquito bite: effect of viral dose |journal=Am. J. Trop. Med. Hyg.|volume=75 |issue=2 |pages=337–45 |year=2006 |pmid=16896145 |doi=10.4269/ajtmh.2006.75.337 |doi-access=free }}</ref><ref name="pmid16553552">{{cite journal|vauthors=Schneider BS, Soong L, Girard YA, Campbell G, Mason P, Higgs S |title=Potentiation of West Nile encephalitis by mosquito feeding |journal=Viral Immunol. |volume=19 |issue=1|pages=74–82 |year=2006 |pmid=16553552|doi=10.1089/vim.2006.19.74|s2cid=37464180 }}</ref>  Mosquitoes inoculate their saliva into the skin while obtaining blood. Mosquito saliva is a pharmacological cocktail of secreted molecules, principally proteins, that can affect vascular constriction, [[blood coagulation]], [[platelet aggregation]], [[inflammation]], and [[Immunity (medical)|immunity]]. It clearly alters the [[immune response]] in a manner that may be advantageous to a virus.<ref name="pmid15541033">{{cite journal |vauthors=Wasserman HA, Singh S, Champagne DE |title=Saliva of the Yellow Fever mosquito, ''Aedes aegypti'', modulates murine lymphocyte function|journal=Parasite Immunol. |volume=26 |issue=6–7 |pages=295–306 |year=2004|pmid=15541033 |doi=10.1111/j.0141-9838.2004.00712.x|s2cid=32742815}}</ref><ref name="pmid12693849">{{cite journal |vauthors=Limesand KH, Higgs S, Pearson LD, Beaty BJ |title=Effect of mosquito salivary gland treatment on vesicular stomatitis New Jersey virus replication and interferon alpha/beta expression in vitro |journal=J. Med. Entomol.|volume=40|issue=2 |pages=199–205 |year=2003 |pmid=12693849 |doi=10.1603/0022-2585-40.2.199|s2cid=85624297 |doi-access=free }}</ref><ref name="pmid15189245">{{cite journal |vauthors=Wanasen N, Nussenzveig RH, Champagne DE, Soong L, Higgs S |title=Differential modulation of murine host immune response by salivary gland extracts from the mosquitoes ''Aedes aegypti'' and ''Culex quinquefasciatus'' |journal=Med. Vet. Entomol.|volume=18 |issue=2 |pages=191–9 |year=2004 |pmid=15189245|doi=10.1111/j.1365-2915.2004.00498.x|s2cid=42458052 }}</ref><ref name="pmid10081770">{{cite journal |vauthors=Zeidner NS, Higgs S, Happ CM, Beaty BJ, Miller BR |title=Mosquito feeding modulates Th1 and Th2 cytokines in flavivirus susceptible mice: an effect mimicked by injection of sialokinins, but not demonstrated in flavivirus resistant mice|journal=Parasite Immunol. |volume=21 |issue=1 |pages=35–44 |year=1999 |pmid=10081770 | doi = 10.1046/j.1365-3024.1999.00199.x|s2cid=26774722|url=https://zenodo.org/record/1236522}}</ref> Studies have shown it can specifically modulate the immune response during early virus infection,<ref name="pmid15671753">{{cite journal |vauthors=Schneider BS, Soong L, Zeidner NS, Higgs S |title=''Aedes aegypti'' salivary gland extracts modulate anti-viral and TH1/TH2 cytokine responses to sindbis virus infection |journal=Viral Immunol. |volume=17 |issue=4 |pages=565–73 |year=2004|pmid=15671753|doi=10.1089/vim.2004.17.565}}</ref> and mosquito feeding can exacerbate WNV infection, leading to higher [[viremia]] and more severe forms of disease.<ref name="pmid18000543"/><ref name="pmid16896145"/><ref name="pmid16553552"/>

====Vertical transmission====
[[Vertical transmission]], the transmission of a viral or bacterial disease from the female of the species to her offspring, has been observed in various West Nile virus studies, amongst different species of mosquitoes in both the laboratory and in nature.<ref>{{cite journal | first = LM | last = Bugbee |author2=Forte LR  |date=September 2004 | title = The discovery of West Nile virus in overwintering ''Culex pipiens'' (Diptera: Culicidae) mosquitoes in Lehigh County, Pennsylvania|journal = Journal of the American Mosquito Control Association | volume = 20 | issue = 3 | pages = 326–7 | pmid = 15532939}}</ref> Mosquito progeny infected vertically in autumn may potentially serve as a mechanism for WNV to overwinter and initiate [[enzootic]] [[Horizontal disease transmission|horizontal]] transmission the following spring, although it likely plays little role in transmission in the summer and fall.<ref>{{cite journal |vauthors=Goddard LB, Roth AE, Reisen WK, Scott TW |title=Vertical transmission of West Nile Virus by three California Culex (Diptera: Culicidae) species |journal=J. Med. Entomol. |volume=40 |issue=6 |pages=743–6 |date=November 2003 |pmid=14765647 |doi=10.1603/0022-2585-40.6.743 |doi-access=free }}</ref>

===Risk factors===
Risk factors independently associated with developing a clinical infection with WNV include infants, having a [[immunodeficiency|weak immune system]], and a patient history of organ transplantation.<ref name=Jong.71>{{cite book |first1=Nicole|last1=Lindsey|first2=Emily|last2=McDonald|first3=Marc|last3=Fischer|first4=J. Erin|last4=Staples|editor1-last=Jong |editor1-first=Elaine C. |editor2-last=Stevens |editor2-first=Dennis L. |title=Netter's Infectious Diseases |date=2022 |publisher=Elsevier |location=Philadelphia |isbn=978-0-323-71159-3 |pages=422–427|edition=2nd |chapter-url=https://books.google.com/books?id=l8skEAAAQBAJ&pg=PA422|language=en |chapter=71. West Nile virus Disease}}</ref><ref>{{cite journal  |vauthors=Kumar D, Drebot MA, Wong SJ, etal |title=A seroprevalence study of West Nile virus infection in solid organ transplant recipients |journal=Am. J. Transplant. |volume=4|issue=11 |pages=1883–8 |year=2004 |pmid=15476490 |doi=10.1111/j.1600-6143.2004.00592.x |s2cid=31695008 |doi-access= }}</ref>   For neuroinvasive disease the additional risk factors include older age (>50+), male sex, [[hypertension]], and [[diabetes mellitus]].<ref>{{cite journal |vauthors=Jean CM, Honarmand S, Louie JK, Glaser CA |title=Risk factors for West Nile virus neuroinvasive disease, California, 2005 |journal=Emerging Infect. Dis. |volume=13 |issue=12 |pages=1918–20 |date=December 2007 |pmid=18258047 |pmc=2876738 |doi=10.3201/eid1312.061265 }}</ref><ref>{{cite journal  |vauthors=Kumar D, Drebot MA, Wong SJ, etal |title=A seroprevalence study of west nile virus infection in solid organ transplant recipients |journal=Am. J. Transplant. |volume=4|issue=11 |pages=1883–8 |year=2004 |pmid=15476490 |doi=10.1111/j.1600-6143.2004.00592.x |s2cid=31695008 |doi-access= }}</ref>

A genetic factor also appears to increase susceptibility to West Nile disease. A mutation of the gene ''[[CCR5]]'' gives some protection against [[HIV]] but leads to more serious complications of WNV infection. Carriers of two mutated copies of ''CCR5'' made up 4.0 to 4.5% of a sample of people with West Nile disease, while the incidence of the gene in the general population is only 1.0%.<ref>{{cite journal | first = WG | last = Glass |author2=Lim JK |author3=Cholera R |author4=Pletnev AG |author5=Gao JL |author6=Murphy PM  | date = October 17, 2005 | title = Chemokine receptor CCR5 promotes leukocyte trafficking to the brain and survival in West Nile virus infection | journal = Journal of Experimental Medicine | volume = 202 | issue = 8 | pages = 1087–98 | pmid = 16230476 | doi = 10.1084/jem.20042530 | pmc = 2213214}}</ref><ref>{{cite journal | first = WG | last = Glass |author2=McDermott DH |author3=Lim JK |author4=Lekhong S |author5=Yu SF |author6=Frank WA |author7=Pape J |author8=Cheshier RC |author9=Murphy PM   | date = January 23, 2006 | title = CCR5 deficiency increases risk of symptomatic West Nile virus infection | journal = Journal of Experimental Medicine | volume = 203 | issue = 1 | pages = 35–40 | pmid = 16418398 | doi = 10.1084/jem.20051970 | pmc = 2118086}}</ref>

The most at risk occupations in the U.S. are outdoor workers, for example farmers, loggers, landscapers/groundskeepers, construction workers, painters, summer camp workers and pavers.<ref>{{Cite web|url=https://www.osha.gov/dts/shib/shib082903b.html|title=Safety and Health Information Bulletins {{!}} Workplace Precautions Against West Nile Virus {{!}} Occupational Safety and Health Administration|website=www.osha.gov|language=en-us|access-date=2018-11-28}}</ref> Two reports of accidental exposure by laboratory personnel working with infected fluids or tissues have been received. While this appears to be a rare occurrence, it highlights the need for proper handling of infected materials. The [[World Health Organization]] states that there are no known cases of health care workers acquiring the virus from infected patients when the appropriate infection control precautions are observed.<ref>{{Cite web|url=https://www.who.int/news-room/fact-sheets/detail/west-nile-virus|title=West Nile virus|website=World Health Organization|language=en-US|access-date=2018-11-28}}</ref>

==Diagnosis==
[[File:IgM.png|thumb|An [[IgM|immunoglobulin M]] [[antibody]] [[molecule]]: Definitive diagnosis of WNV is obtained through detection of virus-specific IgM and [[Neutralizing antibody|neutralizing antibodies]].]]
Preliminary diagnosis is often based on the patient's clinical symptoms, places and dates of travel (if patient is from a non[[endemic]] country or area), activities, and [[epidemiology|epidemiologic]] history of the location where infection occurred. A recent history of mosquito bites and an acute febrile illness associated with neurologic signs and symptoms should cause clinical suspicion of WNV.<ref>{{Citation |last1=Zekar |first1=Lara |title=Plasmodium Falciparum Malaria |date=2022 |url=http://www.ncbi.nlm.nih.gov/books/NBK555962/ |work=StatPearls |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=32310422 |access-date=2022-06-24 |last2=Sharman |first2=Tariq}}</ref>

Diagnosis of West Nile virus infections is generally accomplished by [[serology|serologic]] testing of [[blood serum]] or [[cerebrospinal fluid]] (CSF), which is obtained via a [[lumbar puncture]]. Initial screening could be done using the ELISA technique detecting immunoglobulins in the sera of the tested individuals.<ref name="auto"/>

Typical findings of WNV infection include [[lymphocytic pleocytosis]], elevated [[protein]] level, reference [[glucose]] and [[lactic acid]] levels, and no [[erythrocytes]].<ref name=":0">{{Cite book |last1=Rea |first1=William J. |url=https://books.google.com/books?id=aD0PEAAAQBAJ |title=Reversibility of Chronic Disease and Hypersensitivity, Volume 5: Treatment Options of Chemical Sensitivity |last2=Patel |first2=Kalpana D. |date=2017-12-14 |publisher=CRC Press |isbn=978-1-4987-8137-4 |pages=699–700 |language=en}}</ref>

Definitive diagnosis of WNV is obtained through detection of virus-specific [[antibody]] IgM and [[Neutralizing antibody|neutralizing antibodies]]. Cases of West Nile virus meningitis and encephalitis that have been serologically confirmed produce similar degrees of CSF pleocytosis and are often associated with substantial CSF [[neutrophilia]].<ref>{{cite journal |vauthors=Tyler KL, Pape J, Goody RJ, Corkill M, Kleinschmidt-DeMasters BK |title=CSF findings in 250 patients with serologically confirmed West Nile virus meningitis and encephalitis |journal=Neurology |volume=66 |issue=3 |pages=361–5 |date=February 2006 |pmid=16382032 |doi=10.1212/01.wnl.0000195890.70898.1f |s2cid=37751889 }}</ref>
Specimens collected within eight days following onset of illness may not test positive for West Nile IgM, and testing should be repeated. A positive test for West Nile [[Immunoglobulin G|IgG]] in the absence of a positive West Nile IgM is indicative of a previous flavivirus infection and is not by itself evidence of an acute West Nile virus infection.<ref>{{cite web |title=2012 DOHMH Advisory #8: West Nile Virus |publisher=New York City Department of Health and Mental Hygiene |url=http://www.nyc.gov/html/doh/downloads/pdf/cd/2012/12md08.pdf |date=June 28, 2012 |url-status=live |archive-url=https://web.archive.org/web/20131203000040/http://www.nyc.gov/html/doh/downloads/pdf/cd/2012/12md08.pdf |archive-date=December 3, 2013 }}</ref>

If cases of suspected West Nile virus infection, sera should be collected on both the acute and
convalescent phases of the illness.  Convalescent specimens should be collected 2–3 weeks after acute specimens.

It is common in serologic testing for [[cross-reactivity|cross-reactions]] to occur among flaviviruses such as [[dengue virus]] (DENV) and [[tick-borne encephalitis virus]]; this necessitates caution when evaluating serologic results of flaviviral infections.<ref>{{cite journal |vauthors=Papa A, Karabaxoglou D, Kansouzidou A |title=Acute West Nile virus neuroinvasive infections: cross-reactivity with dengue virus and tick-borne encephalitis virus |journal=J. Med. Virol. |volume=83 |issue=10 |pages=1861–5 |date=October 2011 |pmid=21837806 |doi=10.1002/jmv.22180 |s2cid=9901472 }}</ref>

Four [[Food and Drug Administration|FDA]]-cleared WNV IgM [[ELISA]] kits are commercially available from different manufacturers in the U.S., each of these kits is indicated for use on serum to aid in the presumptive laboratory diagnosis of WNV infection in patients with clinical symptoms of meningitis or encephalitis. Positive WNV test results obtained via use of these kits should be confirmed by additional testing at a state health department laboratory or CDC.<ref>{{Cite book |last=Turgeon |first=Mary Louise |url=https://books.google.com/books?id=pEijDgAAQBAJ&dq=Positive+WNV+test+results+obtained+via+use+of+these+kits+should+be+confirmed+by+additional+testing+at+a+state+health+department+laboratory+or+CDC&pg=PA252 |title=Immunology & Serology in Laboratory Medicine - E-Book |date=2017-04-07 |publisher=Elsevier Health Sciences |isbn=978-0-323-40283-5 |pages=252 |language=en}}</ref>

In fatal cases, [[nucleic acid]] amplification, [[histopathology]] with [[immunohistochemistry]], and virus culture of [[autopsy]] tissues can also be useful. Only a few state laboratories or other specialized laboratories, including those at CDC, are capable of doing this specialized testing.<ref>{{Cite book |last1=Long |first1=Sarah S. |url=https://books.google.com/books?id=Xw7VDgAAQBAJ |title=Principles and Practice of Pediatric Infectious Diseases |last2=Prober |first2=Charles G. |last3=Fischer |first3=Marc |date=2017-05-09 |publisher=Elsevier Health Sciences |isbn=978-0-323-46132-0 |pages=1135 |language=en}}</ref>
{{Clear}}

===Differential diagnosis===
A number of various diseases may present with symptoms similar to those caused by a clinical West Nile virus infection. Those causing neuroinvasive disease symptoms include the [[enteroviruses|enterovirus infection]] and bacterial meningitis. Accounting for [[differential diagnoses]] is a crucial step in the definitive diagnosis of WNV infection. Consideration of a differential diagnosis is required when a patient presents with unexplained febrile illness, extreme headache, encephalitis or meningitis. Diagnostic and serologic laboratory testing using [[polymerase chain reaction]] (PCR) testing and [[viral culture]] of CSF to identify the specific pathogen causing the symptoms, is the only currently available means of differentiating between causes of encephalitis and meningitis.<ref name="auto"/>

==Prevention==

[[Image:Mosquito Netting.jpg|thumb|Low-cost, ceiling-hung [[mosquito netting]] for a bed]]
Many of the guidelines for preventing occupational West Nile virus exposure are common to all [[mosquito-borne disease]]s.<ref name=CDC2018Pre>{{Cite web|url=https://www.cdc.gov/westnile/prevention/index.html|title=Prevention {{!}} West Nile Virus {{!}} CDC|date=2018-09-24|website=www.cdc.gov|language=en-us|access-date=2018-11-28}}</ref>

Public health measures include taking steps to reduce mosquito populations. Personal recommendations are to reduce the likelihood of being bitten. General measures to avoid bites include:
* Using insect repellent on exposed skin to repel mosquitoes. Repellents include products containing [[DEET]] and [[picaridin]]. DEET concentrations of 30% to 50% are effective for several hours. Picaridin, available at 7% and 15% concentrations, needs more frequent application. DEET formulations as high as 30% are recommended for children over two months of age.<ref>{{cite web|author1=American Academy of Pediatrics|title=Choosing an Insect Repellent for Your Child|url=https://www.healthychildren.org/English/safety-prevention/at-play/Pages/Insect-Repellents.aspx|website=healthychildren.org|access-date=24 August 2016|date=8 August 2012|url-status=live|archive-url=https://web.archive.org/web/20160827225733/https://www.healthychildren.org/English/safety-prevention/at-play/Pages/Insect-Repellents.aspx|archive-date=27 August 2016}}</ref> The CDC also recommends the use of: IR3535, oil of lemon eucalyptus, para-menthane-diol, or 2-undecanone.<ref>{{Cite web|url=https://www.cdc.gov/westnile/prevention/index.html|title=Prevention {{!}} West Nile Virus {{!}} CDC|date=2018-09-24|website=www.cdc.gov|language=en-us|access-date=2018-10-29}}</ref>  Protect infants less than two months of age by using a carrier draped with [[mosquito netting]] with an elastic edge for a tight fit.
* When using [[sunscreen]], apply sunscreen first and then repellent. Repellent should be washed off at the end of the day before going to bed.<ref>{{Cite book |last1=Richman |first1=Douglas D. |url=https://books.google.com/books?id=G9zIDwAAQBAJ |title=Clinical Virology |last2=Whitley |first2=Richard J. |last3=Hayden |first3=Frederick G. |date=2016-12-01 |publisher=John Wiley & Sons |isbn=978-1-68367-316-3 |language=en}}</ref>
* Wear long-sleeve shirts, which should be tucked in, long trousers, socks, and hats to cover exposed skin (although most fabrics do not totally protect against bites). Insect repellents should be applied over top of protective clothing for greater protection. Do not apply insect repellents underneath clothing.<ref>{{Cite book |last=Auerbach |first=Paul S. |url=https://books.google.com/books?id=pniCBxIQIHsC |title=Medicine for the Outdoors: The Essential Guide to First Aid and Medical Emergencies |date=2009-01-01 |publisher=Elsevier Health Sciences |isbn=978-0-323-06813-0 |pages=392 |language=en}}</ref>
* Repellents containing [[permethrin]] (''e.g.'', Permanone) or other insect repellents may be applied to clothing, shoes, tents, mosquito nets, and other gear. (Permethrin is not suitable for use directly on skin.) Most repellent is generally removed from clothing and gear by a single washing, but permethrin-treated clothing is effective for up to five washings.<ref name=":0" />
* Most mosquitoes that transmit disease are most active at dawn and in the evening dusk. A notable exception is the [[Asian tiger mosquito]], which is a daytime feeder and is more apt to be found in, or on the periphery of, shaded areas with heavy vegetation. They are now widespread in the United States, and in Florida they have been found in all 67 counties.<ref name=A_albopictus/>
* In an at-risk area, staying in air-conditioned or well-[[Window screen|screened]] room, or sleeping under an insecticide-treated [[Mosquito net|bed net]] is recommended. Bed nets should be tucked under mattresses, and can be sprayed with a repellent if not already treated with an insecticide.<ref name=CDC2018Pre/>

===Monitoring and control===
West Nile virus can be sampled from the environment by the pooling of trapped mosquitoes via [[ovitrap]]s, [[carbon dioxide]]-baited light traps, and [[gravid]] traps, testing blood samples drawn from wild birds, dogs, and sentinel monkeys, and testing brains of dead birds found by various animal control agencies and the public.{{cn|date=September 2022}}

Testing of the mosquito samples requires the use of reverse-transcriptase PCR ([[RT-PCR]]) to directly amplify and show the presence of virus in the submitted samples. When using the blood sera of wild birds and sentinel chickens, samples must be tested for the presence of WNV [[antibodies]] by use of [[immunohistochemistry]] (IHC)<ref>{{cite journal | first = M | last = Jozan |author2=Evans R |author3=McLean R |author4=Hall R |author5=Tangredi B |author6=Reed L |author7=Scott J  |date=Fall 2003 | title = Detection of West Nile virus infection in birds in the United States by blocking ELISA and immunohistochemistry | journal = Vector-Borne and Zoonotic Diseases |volume = 3 | issue = 3 | pages = 99–110 | pmid = 14511579 | doi = 10.1089/153036603768395799| s2cid = 17720540 | url = https://digitalcommons.unl.edu/icwdm_usdanwrc/249 | type = Submitted manuscript }}</ref> or [[enzyme-linked immunosorbent assay]] (ELISA).<ref>{{cite journal | first = RA | last = Hall |author2=Broom AK |author3=Hartnett AC |author4=Howard MJ |author5=Mackenzie JS  |date=February 1995 | title = Immunodominant epitopes on the NS1 protein of MVE and KUN viruses serve as targets for a blocking ELISA to detect virus-specific antibodies in sentinel animal serum | journal = Journal of Virological Methods | volume = 51 | issue = 2–3 | pages = 201–10 | pmid = 7738140 | doi = 10.1016/0166-0934(94)00105-P}}</ref>

Dead birds, after [[necropsy]], or their oral swab samples collected on specific RNA-preserving filter paper card,<ref>{{Cite web |title=California Department of Public Health Tutorial for Local Agencies to Safely Collect Dead Birds Oral Swab Samples on RNAse Cards for West Nile Virus Testing |url=http://www.westnile.ca.gov/downloads.php?download_id=2949&filename=RNAse_tutorial.pdf |url-status=dead |archiveurl=https://web.archive.org/web/20140709075706/http://westnile.ca.gov/downloads.php?download_id=2949&filename=RNAse_tutorial.pdf |archivedate=July 9, 2014}}</ref><ref>[http://www.fortiusbio.com/RNA_Sampling_Card.html RNA virus preserving filter paper card] {{webarchive|url=https://web.archive.org/web/20160110095447/http://fortiusbio.com/RNA_Sampling_Card.html |date=2016-01-10 }}. fortiusbio.com</ref> can have their virus presence tested by either RT-PCR or IHC, where virus shows up as brown-stained tissue because of a substrate-[[enzyme]] reaction.

West Nile control is achieved through [[mosquito control]], by elimination of mosquito breeding sites such as abandoned pools, applying [[larvacide]] to active breeding areas, and targeting the adult population via [[lethal ovitrap]]s and [[aerial spraying]] of [[pesticide]]s.<ref>{{Cite book |last1=Dusfour |first1=Isabelle |url=https://library.oapen.org/bitstream/handle/20.500.12657/50200/9781000435085.pdf?sequence=1#page=236 |title=Mosquitopia: The place of pests in a healthy world |last2=Chaney |first2=Sarah C |publisher=[[Routledge]] |year=2022 |isbn=978-1-00-305603-4 |location=New York |pages=213–233 |language=English |chapter=14 - MOSQUITO CONTROL: Success, failure and expectations in the context of arbovirus expansion and emergence |doi=}}</ref><ref>{{Cite journal |last=Tidi |first=Stephen K |date=December 6, 2015 |title=Mosquito control: A review |url=http://www.brsfoundation.org/brtw/archive/2015-2016/volume_1/brtw-2015-1-97-105.pdf |archive-url=https://web.archive.org/web/20200321051133id_/http://www.brsfoundation.org/brtw/archive/2015-2016/volume_1/brtw-2015-1-97-105.pdf |url-status=usurped |archive-date=2020-03-21 |journal=Biosciences Research in Today's World |issn=2476-7905}}</ref><ref>{{Cite journal |last1=Wooding |first1=Madelien |last2=Naudé |first2=Yvette |last3=Rohwer |first3=Egmont |last4=Bouwer |first4=Marc |date=2020-02-17 |title=Controlling mosquitoes with semiochemicals: a review |journal=Parasites & Vectors |language=en |volume=13 |issue=1 |pages=80 |doi=10.1186/s13071-020-3960-3 |doi-access=free |issn=1756-3305 |pmc=7027039 |pmid=32066499}}</ref> With aerial pesticides, there is a rising need to develop new versions as [[pesticide resistance]] among mosquitoes can occur.<ref>{{Cite journal |last1=Karunaratne |first1=S. H. P. P. |last2=Surendran |first2=S. N. |date=2022 |title=Mosquito control: A review on the past, present and future strategies |url=http://repo.lib.jfn.ac.lk/ujrr/handle/123456789/8969 |journal=Journal of the National Science Foundation of Sri Lanka |volume=50 |page=277 |doi=10.4038/jnsfsr.v50i0.11244 |language=en|doi-access=free }}</ref><ref>{{Cite journal |last1=Dahmana |first1=Handi |last2=Mediannikov |first2=Oleg |date=March 13, 2020 |title=Mosquito-Borne Diseases Emergence/Resurgence and How to Effectively Control It Biologically |journal=Pathogens |language=en |volume=9 |issue=4 |pages=310 |doi=10.3390/pathogens9040310 |doi-access=free |pmid=32340230 |pmc=7238209 |issn=2076-0817}}</ref>

[[Environmentalist]]s have condemned attempts to control the transmitting mosquitoes by spraying pesticide, saying the detrimental health effects of spraying outweigh the relatively few lives that may be saved, and more environmentally friendly ways of controlling mosquitoes are available. They also question the effectiveness of insecticide spraying, as they believe mosquitoes that are resting or flying above the level of spraying will not be killed; the most common vector in the northeastern United States, ''Culex pipiens'', is a [[Canopy (forest)|canopy]] feeder.{{cn|date=January 2023}}
<gallery>
File:CDC-LightTrap 200.jpg|A [[carbon dioxide]]-baited CDC light trap at [[National Park Service|NPS]]monitoring site: The highest individual light trap total for 2010 was from a trap located in a [[salt marsh]] in the [[Fire Island National Seashore]]: around 25,142 mosquitoes were collected during a 16-hour period on August 31.<ref>{{cite web|title=Mosquito Monitoring and Management|url=http://www.nps.gov/fiis/parkmgmt/mosquito-management.htm|publisher=National Park Service|url-status=live|archive-url=https://web.archive.org/web/20130415112435/http://www.nps.gov/fiis/parkmgmt/mosquito-management.htm|archive-date=2013-04-15}}</ref>
File:Culex sp larvae.png|[[Insect egg|Eggs]] of permanent water [[mosquito]]es can hatch, and the [[larvae]] survive, in only a few ounces of water. Less than half the amount that may collect in a discarded coffee cup. [[Flood]]water species lay their eggs on wet soil or other moist surfaces. Hatch time is variable for both types; under favorable circumstances (such as warm weather), the eggs of some species may hatch in as few as 1–3 days after [[Oviposition|being laid]].<ref>[[Oklahoma State University]]: Mosquitoes and West Nile virus</ref>
File:Used tires.jpg|Used [[tires]] often hold [[stagnant water]] and are a breeding ground for many [[species]] of mosquitoes. Some species such as the [[Aedes albopictus|Asian tiger mosquito]] prefer manmade containers, such as tires, in which to lay their eggs. The rapid spread of this aggressive daytime feeding species [[Invasive species|beyond their native range]] has been attributed to the used tire trade.<ref name=A_albopictus>{{cite web |vauthors=Rios L, Maruniak JE |title=Asian Tiger Mosquito, ''Aedes albopictus'' (Skuse) (Insecta: Diptera: Culicidae) |date=October 2011 |publisher=Department of Entomology and Nematology, University of Florida |url=http://edis.ifas.ufl.edu/in594 |id=EENY-319 |url-status=live |archive-url=https://web.archive.org/web/20120926113428/http://edis.ifas.ufl.edu/in594 |archive-date=2012-09-26 }}</ref><ref>{{cite journal |vauthors=Benedict MQ, Levine RS, Hawley WA, Lounibos LP |title=Spread of the tiger: global risk of invasion by the mosquito ''Aedes albopictus'' |journal=Vector-Borne and Zoonotic Diseases |volume=7 |issue=1 |pages=76–85 |year=2007 |pmid=17417960 |pmc=2212601 |doi=10.1089/vbz.2006.0562 }}</ref>
</gallery>

==Treatment==
No specific treatment is available for WNV infection.<ref name="petersen">{{cite journal |vauthors=Petersen LR, Brault AC, Nasci RS |title=West Nile virus: review of the literature |journal=JAMA |volume=310 |issue=3 |pages=308–15 |date=July 2013 |pmid=23860989 |pmc=4563989 |doi=10.1001/jama.2013.8042 |url=}}</ref> Most people recover without treatment.<ref>{{cite web|title=West Nile Virus|url=https://medlineplus.gov/westnilevirus.html#cat_69|website=[[MedlinePlus]]|date=18 March 2021|access-date=21 October 2021}}</ref> In mild cases, over-the-counter pain relievers can help ease mild headaches and muscle aches in adults.<ref>{{Cite web |date=2021-07-22 |title=Symptoms, Diagnosis, & Treatment {{!}} West Nile Virus {{!}} CDC |url=https://www.cdc.gov/westnile/symptoms/index.html |access-date=2022-06-24 |website=www.cdc.gov |language=en-us}}</ref> In severe cases supportive care is provided, often in hospital, with [[intravenous fluids]], pain medication, respiratory support, and prevention of secondary infections.<ref name="sambri">{{cite journal |vauthors=Sambri V, Capobianchi M, Charrel R, Fyodorova M, Gaibani P, Gould E, Niedrig M, Papa A, Pierro A, Rossini G, Varani S, Vocale C, Landini MP |title=West Nile virus in Europe: emergence, epidemiology, diagnosis, treatment, and prevention |journal=Clin Microbiol Infect |volume=19 |issue=8 |pages=699–704 |date=August 2013 |pmid=23594175 |doi=10.1111/1469-0691.12211 |url=|doi-access=free }}</ref>

==Prognosis==
While the general prognosis is favorable, current studies indicate that West Nile Fever can often be more severe than previously recognized, with studies of various recent outbreaks indicating that it may take as long as 60 to 90 days to recover.<ref name=Carson06/><ref>{{cite journal  |vauthors=Watson JT, Pertel PE, Jones RC, etal |title=Clinical characteristics and functional outcomes of West Nile Fever |journal=Ann. Intern. Med. |volume=141 |issue=5 |pages=360–5 |date=September 2004 |pmid=15353427 |doi=10.7326/0003-4819-141-5-200409070-00010|s2cid=5779034 }}</ref> Patients with milder WNF are just as likely as those with more severe manifestations of neuroinvasive disease to experience multiple [[Somatic nervous system|somatic]] complaints such as tremor, and dysfunction in [[motor skill]]s and [[executive functions]] for over a year. People with milder symptoms are just as likely as people with more severe symptoms to experience adverse outcomes.<ref>{{cite journal  |vauthors=Klee AL, Maidin B, Edwin B, etal |date=Aug 2004 | title = Long-term prognosis for clinical West Nile virus infection | journal = Emerg Infect Dis | volume = 10 | issue = 8| pages = 1405–11 | pmid = 15496241 | doi = 10.3201/eid1008.030879 | pmc = 3320418 }}</ref> Recovery is marked by a long [[convalescence]] with [[Fatigue (medical)|fatigue]].  One study found that neuroinvasive WNV infection was associated with an increased risk for subsequent kidney disease.<ref>{{cite journal |author=Nolan MS, Podoll AS, Hause AM, Akers KM, Finkel KW, Murray KO |title=Prevalence of chronic kidney disease and progression of disease over time among patients enrolled in the Houston West Nile virus cohort |journal=PLOS ONE |volume=7 |issue=7 |pages=e40374 |year=2012 |pmid=22792293 |pmc=3391259 |doi=10.1371/journal.pone.0040374 |editor1-last=Wang |editor1-first=Tian|bibcode=2012PLoSO...740374N |doi-access=free }}</ref><ref>{{cite web  |url= http://guardianlv.com/2012/08/new-study-reveals-west-nile-virus-is-far-more-menacing-harms-far-more-people/  |title= New Study Reveals: West Nile virus is far more menacing & harms far more people  |date= 26 August 2012  |work= The Guardian Express  |access-date= 26 August 2012  |url-status= live  |archive-url= https://web.archive.org/web/20121006012354/http://guardianlv.com/2012/08/new-study-reveals-west-nile-virus-is-far-more-menacing-harms-far-more-people/  |archive-date= 6 October 2012  }}</ref>

==Epidemiology==
[[Image:Global distribution of West Nile virus-CDC.gif|thumb|upright=1.4|Global distribution of West Nile virus (2006)]]
{{See also|List of West Nile virus outbreaks|West Nile virus in the United States}}

WNV was first isolated from a feverish 37-year-old woman at Omogo in the [[West Nile sub-region|West Nile District]] of [[Uganda]] in 1937 during research on [[yellow fever virus]].<ref>{{cite journal |vauthors=Smithburn KC, Hughes TP, Burke AW, Paul JH |title=A Neurotropic Virus Isolated from the Blood of a Native of Uganda |journal=Am. J. Trop. Med. |volume=20 |issue=1|pages=471–92 |date=June 1940|doi=10.4269/ajtmh.1940.s1-20.471 |doi-access=free }}</ref>  A series of [[serosurvey]]s in 1939 in central Africa found anti-WNV positive results ranging from 1.4% (Congo) to 46.4% (White Nile region, Sudan). 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]]<ref>{{cite journal |vauthors=Work TH, Hurlbut HS, Taylor RM |title=Isolation of West Nile virus from hooded crow and rock pigeon in the Nile delta |journal=Proc. Soc. Exp. Biol. Med. |volume=84 |issue=3|pages=719–22 |year=1953 |pmid=13134268 |doi=10.3181/00379727-84-20764 |s2cid=45962741 }}</ref> and [[Israel]].<ref>{{cite journal |vauthors=Bernkopf H, Levine S, Nerson R |title=Isolation of West Nile virus in Israel |journal=J. Infect. Dis. |volume=93 |issue=3 |pages=207–18 |year=1953|pmid=13109233 |doi=10.1093/infdis/93.3.207 }}</ref> 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.{{cn|date=September 2022}}

The first appearance of WNV in the Western Hemisphere was in 1999<ref name=Nash01>{{cite journal  |vauthors=Nash D, Mostashari F, Fine A, etal |title=The outbreak of West Nile virus infection in the New York City area in 1999 |journal=N. Engl. J. Med. |volume=344 |issue=24 |pages=1807–14 |date=June 2001 |pmid=11407341 |doi=10.1056/NEJM200106143442401|url=https://academicworks.cuny.edu/sph_pubs/24 |doi-access=free }}</ref>  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. The American outbreak began in [[College Point, Queens]] in New York City and was later spread to the neighboring states of [[New Jersey]] and [[Connecticut]]. The virus is believed to have entered in an infected bird or mosquito, although there is no clear evidence.<ref>{{cite journal |author=Calisher CH |author1-link=Charles Calisher|title=West Nile virus in the New World: appearance, persistence, and adaptation to a new econiche—an opportunity taken |journal=Viral Immunol.|volume=13 |issue=4 |pages=411–4 |year=2000 |pmid=11192287 |doi=10.1089/vim.2000.13.411 }}</ref>  West Nile virus is now [[endemic]] in Africa, Europe, the Middle East, west and central Asia, Oceania (subtype [[Kunjin virus|Kunjin]]), and most recently, North America and is spreading into Central and South America.<ref>{{Cite book |url=https://books.google.com/books?id=7_vDDwAAQBAJ |title=Encyclopedia of Environmental Health |date=2019-08-22 |publisher=Elsevier |isbn=978-0-444-63952-3 |pages=452 |language=en}}</ref>

Outbreaks of West Nile virus encephalitis in humans have occurred in [[Algeria]] (1994), [[Romania]] (1996 to 1997), the Czech Republic (1997), [[Democratic Republic of the Congo|Congo]] (1998), Russia (1999), the United States (1999 to 2009), Canada (1999–2007), Israel (2000), Greece (2010), and Israel (2024).<ref>{{Cite book |last1=Bisen |first1=Prakash S. |url=https://books.google.com/books?id=FpoZGznXhTAC |title=Emerging Epidemics: Management and Control |last2=Raghuvanshi |first2=Ruchika |date=2013-06-14 |publisher=John Wiley & Sons |isbn=978-1-118-39325-3 |language=en}}</ref>

[[Epizootic]]s of disease in horses occurred in [[Morocco]] (1996), Italy (1998), the United States (1999 to 2001), and France (2000), Mexico (2003) and [[Sardinia]] (2011).{{cn|date=January 2023}}

In August 2024 in [[Warsaw]] the West Nile virus was identified in bodies of dead birds ([[Corvidae]]) while investigating an unusually high number of finds.<ref>{{Cite web|url = https://www.polsatnews.pl/wiadomosc/2024-08-13/tajemnicza-choroba-ptakow-w-warszawie-potwierdzily-sie-zle-informacje/|title = Tajemnicza choroba ptaków w Warszawie. Potwierdziły się złe informacje|date = August 13, 2024}}</ref>

Outdoor workers (including biological fieldworkers, construction workers, farmers, landscapers, and painters), healthcare personnel, and laboratory personnel who perform necropsies on animals are at risk of contracting WNV.<ref>{{Cite web|url = https://www.cdc.gov/niosh/topics/westnile/|title = West Nile virus|date = August 27, 2012|publisher = NIOSH|url-status = live|archive-url = https://web.archive.org/web/20170729073111/https://www.cdc.gov/niosh/topics/westnile/|archive-date = July 29, 2017}}</ref>

In 2012, the US experienced one of its worst [[epidemic]]s in which 286 people died, with the state of Texas being hard hit by this virus.<ref name="pmid24210089">{{cite journal |vauthors=Murray KO, Ruktanonchai D, Hesalroad D, Fonken E, Nolan MS |title=West Nile virus, Texas, USA, 2012 |journal=Emerging Infectious Diseases |volume=19 |issue=11 |pages=1836–8 |date=November 2013  |pmid=24210089 |pmc=3837649 |doi=10.3201/eid1911.130768 }}</ref><ref>{{cite news|title=2012 was deadliest year for West Nile in US, CDC says|author=Fox, M.|url=http://vitals.nbcnews.com/_news/2013/05/13/18232095-2012-was-deadliest-year-for-west-nile-in-us-cdc-says|newspaper=NBC News|date=May 13, 2013|access-date=May 13, 2013|url-status=live|archive-url=https://web.archive.org/web/20130608042431/http://vitals.nbcnews.com/_news/2013/05/13/18232095-2012-was-deadliest-year-for-west-nile-in-us-cdc-says|archive-date=June 8, 2013}}</ref>

=== Weather ===
Drought has been associated with a higher number of West Nile virus cases in the following year.<ref name=Bro2014>{{Cite journal|last1=Brown|first1=L.|last2=Medlock|first2=J.|last3=Murray|first3=V.|date=January 2014|title=Impact of drought on vector-borne diseases – how does one manage the risk?|journal=Public Health|volume=128|issue=1|pages=29–37|doi=10.1016/j.puhe.2013.09.006|pmid=24342133|issn=0033-3506}}</ref> As drought can decrease fish and other populations that eat mosquito eggs, higher numbers of mosquitoes can result.<ref name=Bro2014/> Higher temperatures are linked to decreased time for replication and increased viral load in birds and mosquitoes.<ref name=Paz2015>{{Cite journal|last=Paz|first=Shlomit|date=2015-04-05|title=Climate change impacts on West Nile virus transmission in a global context|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|volume=370|issue=1665|pages=20130561|doi=10.1098/rstb.2013.0561|issn=0962-8436|pmid=25688020|pmc=4342965}}</ref>

==Research==
A vaccine for horses ([[ATCvet]] code: {{ATCvet|I05|AA10}}) based on killed viruses exists; some [[zoo]]s have given this vaccine to their birds, although its effectiveness is unknown. Dogs and cats show few if any signs of infection. There have been no known cases of direct canine-human or feline-human transmission; although these pets can become infected, it is unlikely they are, in turn, capable of infecting native mosquitoes and thus continuing the disease cycle.<ref>{{cite web |title=Vertebrate Ecology |date=30 April 2009 |work=West Nile Virus |publisher=Division of Vector-Borne Diseases, CDC |url=https://www.cdc.gov/ncidod/dvbid/westnile/birds&mammals.htm |url-status=live |archive-url=https://web.archive.org/web/20130301003126/http://www.cdc.gov/ncidod/dvbid/westnile/birds%26mammals.htm |archive-date=1 March 2013 }}</ref> [[AMD3100]], which had been proposed as an antiretroviral drug for HIV, has shown promise against West Nile encephalitis. [[Morpholino]] antisense oligos conjugated to [[cell penetrating peptide]]s have been shown to partially protect mice from WNV disease.<ref>{{cite journal | first = Tia S | last = Deas |author2=Bennett CJ |author3=Jones SA |author4=Tilgner M |author5=Ren P |author6=Behr MJ |author7=Stein DA |author8=Iversen PL |author9=Kramer LD |author10=Bernard KA |author11=Shi PY |date=May 2007 | title = In vitro resistance selection and in vivo efficacy of morpholino oligomers against West Nile virus | journal = Antimicrob Agents Chemother | pmid = 17485503 | doi = 10.1128/AAC.00069-07 | volume = 51 | pages = 2470–82 | issue = 7 | pmc = 1913242}}</ref> There have also been attempts to treat infections using [[ribavirin]], intravenous [[immunoglobulin]], or [[alpha interferon]].<ref>{{cite journal |vauthors=Hayes EB, Sejvar JJ, Zaki SR, Lanciotti RS, Bode AV, Campbell GL |title=Virology, pathology, and clinical manifestations of West Nile virus disease |journal=Emerging Infect. Dis. |volume=11 |issue=8 |pages=1174–9 |year=2005 |pmid=16102303 |doi=10.3201/eid1108.050289b |pmc=3320472 }}</ref> GenoMed, a U.S. biotech company, has found that blocking angiotensin II can treat the "[[cytokine storm]]" of West Nile virus encephalitis as well as other viruses.<ref>{{cite journal |vauthors=Moskowitz DW, Johnson FE |title=The central role of angiotensin I-converting enzyme in vertebrate pathophysiology |journal=Curr Top Med Chem |volume=4 |issue=13 |pages=1433–54 |year=2004 |pmid=15379656 |doi=10.2174/1568026043387818 |s2cid=22897898 }}</ref>

As of 2019, six vaccines had progressed to human trials but none had been licensed in the United States. Only the two live attenuated vaccines produced strong immunity after a single dose.<ref>{{Cite book |last1=Malik |first1=Yashpal Singh |url=https://books.google.com/books?id=v2RXEAAAQBAJ |title=Role of Birds in Transmitting Zoonotic Pathogens |last2=Milton |first2=Arockiasamy Arun Prince |last3=Ghatak |first3=Sandeep |last4=Ghosh |first4=Souvik |date=2022-01-01 |publisher=Springer Nature |isbn=978-981-16-4554-9 |pages=49 |language=en}}</ref>

Dr. Anthony Fauci, former director of the National Institute of Allergy and Infectious Diseases, has urged proactive action, including international collaborations for vaccine and antiviral development, emphasizing that we must not wait for a greater crisis to address this virus. His call for increased public awareness and scientific research followed his own recovery as a victim of the West Nile virus himself, which he most likely contracted in his Washington, D.C.–based backyard from a mosquito bite. <ref>{{Cite news |last=Anthony |first=Fauci |date=October 7, 2024 |title=Anthony Fauci: My West Nile Virus Nightmare |url=https://www.nytimes.com/2024/10/07/opinion/fauci-west-nile-virus.html}}</ref>



{{Clear}}

==References==
{{Reflist}}

== External links ==
{{Commons|West Nile virus}}
{{Portal|Medicine|Viruses}}

* {{cite journal |vauthors=De Filette M, Ulbert S, Diamond M, Sanders NN |title=Recent progress in West Nile virus diagnosis and vaccination |journal=Vet. Res. |volume=43 |issue=1 |pages=16 |year=2012 |pmid=22380523 |pmc=3311072 |doi=10.1186/1297-9716-43-16 |doi-access=free }}
* {{cite web |title=West Nile Virus |publisher=Division of Vector-Borne Diseases, U.S. [[Centers for Disease Control and Prevention]] (CDC) |url=https://www.cdc.gov/ncidod/dvbid/westnile/|date= 2018-10-30}}
* [https://www.cdc.gov/niosh/topics/outdoor/mosquito-borne/westnile.html CDC—West Nile Virus—NIOSH Workplace Safety and Health Topic]
* [https://npic.orst.edu/wnv/ West Nile Virus Resource Guide]—National Pesticide Information Center
* [https://www.viprbrc.org/brc/home.do?decorator=flavi Virus Pathogen Database and Analysis Resource (ViPR): Flaviviridae]
* [https://www.invasivespeciesinfo.gov/profile/west-nile-virus Species Profile – West Nile Virus (''Flavivirus'')], National Invasive Species Information Center, [[United States National Agricultural Library]]. Lists general information and resources for West Nile Virus.

{{Medical resources
|  DiseasesDB  = 30025
|  ICD10       = {{ICD10|A|92|3}}
|  ICD9        = {{ICD9|066.4}}
|  MedlinePlus = 007186
|  MeshID      = D014901
}}
{{Zoonotic viral diseases}}
{{Authority control}}

{{DEFAULTSORT:West Nile Virus}}
[[Category:Horse diseases]]
[[Category:Bird diseases]]
[[Category:Flaviviruses]]
[[Category:Arthropod-borne viral fevers and viral haemorrhagic fevers]]
[[Category:Zoonoses]]
[[Category:Tropical diseases]]
[[Category:Insect-borne diseases]]
[[Category:Animal vaccines]]
[[Category:Encephalitis]]
[[Category:Animal viral diseases]]
[[Category:Wikipedia medicine articles ready to translate]]