West Nile virus

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As of 2006, West Nile virus lived in every yellow country on this map

West Nile Virus (WNV) is a virus that belongs to the genus Flavivirus. It causes an infectious disease called "West Nile virus disease" or just "West Nile virus."[1] WNV mainly infects birds, but it can also infect humans, horses, dogs, bats, cats, reptiles,[2][3] and amphibians.[1]

West Nile virus is spread by mosquitoes, who get the virus from birds. If a mosquito bites a bird that has WNV, and then bites a human, that person can get West Nile Virus.[1]

West Nile virus was first discovered in 1937, in the West Nile area of Uganda, in East Africa.[1] (This is how the virus got its name.) However, before the 1990s, there were very few cases of WNV. Then there was an outbreak in Algeria in 1994 and another in Romania in 1996.[1] By 2004, the virus had spread to North America,[4] the Caribbean islands, and Latin America. It continues to spread through Africa, Asia, Australia, Europe, the Middle East, Canada, and the United States.[4] In 2012, one of the worst West Nile virus epidemics yet happened in the United States; 286 people died.[5][6]

Signs and symptoms[change | change source]

About 80% of people who get West Nile virus have no symptoms.[7]

When a person does get symptoms, they usually do not appear until 2 to 15 days after the person got the virus. (This is called the virus's incubation period.)[7]

West Nile virus can cause many different types of illness. The rarest, but most serious types affect the neurological system - the brain and the nerves. The most common type of illness caused by WNV is West Nile fever, which does not affect the neurological system.

West Nile fever[change | change source]

West Nile fever happens in about 20% of people with WNV. It causes a high fever and flu-like symptoms. Usually, the symptoms are not too bad, and get better after 3 to 6 days. Symptoms may include:[7]

West Nile neuroinvasive disease[change | change source]

Neuroinvasive disease is when the West Nile virus infects the central nervous system (the brain and spinal cord). This happens in less than 1% of people who get West Nile virus.[8] However, in those people, it can cause very serious problems. These problems include:

  • West Nile encephalitis: Encephalitis is swelling in the brain. This can cause confusion, muscle weakness, paralysis, and loss of reflexes. This is the most common type of West Nile neuroinvasive disease.[9][10]
  • West Nile meningitis: Meningitis is inflammation of the meninges, the layers that protect the brain and spinal cord. People with meningitis usually have a bad headache, a high fever, and a stiff neck.[11]
  • West Nile meningoencephalitis: This is inflammation of both the brain and the meninges (encephalitis and meningitis).[11]
  • West Nile poliomyelitis: This causes the arms and legs on one side of the body to suddenly become weak or paralyzed. The person may not have any other symptoms of WNV infection. Sometimes, the breathing muscles can become paralyzed, and the person becomes unable to breathe.[11]
  • West Nile reversible paralysis: This also causes weakness or paralysis on one side of the body, but it almost always gets better.[12]

Other complications[change | change source]

WNV can cause some other complications that do not affect the neurological system. These complications are very uncommon. They include:

Diagnosis[change | change source]

At first, a medical professional usually makes a possible diagnosis of West Nile virus based on a person's symptoms, where they live, and when and where they have traveled. The World Health Organization says that doctors should suspect West Nile virus if a patient:[1]

  • Has a fever that started suddenly; and
  • Has neurological symptoms; and
  • Was recently bitten by mosquitoes.

West Nile virus can be diagnosed for certain by:

Treatment[change | change source]

There is no known treatment or cure for WNV. There are no known anti-viral medications (medicines which kill viruses) which will kill the West Nile virus. Doctors can only provide "supportive care," which means they can only treat the symptoms of WNV. For example, they can give fluids through a needle placed into a vein if a person is very dehydrated; help the person breathe if needed; and give medications to prevent them from getting any other infections.[1]

Transmission[change | change source]

The West Nile virus stays alive in nature by getting spread back and forth between birds and mosquitoes. Birds get WNV more often than any other living things. When a mosquito bites a bird that has WNV, the mosquito gets the virus. Then, if the mosquito bites a bird that does not have WNV, the mosquito can give that bird the virus. In this way, birds and mosquitoes give the virus to each other and keep it alive.[20]

Humans usually get West Nile virus by being bitten by mosquitoes who have gotten the virus from birds. Humans can get the virus from many different species of mosquitoes.[20]

Though this is not common, a person with West Nile virus can give another person the virus. This can happen if:

Prevention[change | change source]

Low-cost mosquito net for a bed

There is no vaccine that will prevent West Nile virus.[1] The best way for people to protect themselves against West Nile virus is to protect themselves against mosquitoes. There are many ways to do this. For example:[26]

  • Using bug spray, especially the type that has DEET in it
  • Wearing long sleeves, long pants, socks, and hats
  • Using a mosquito net over the bed when sleeping
  • Putting bug spray on clothes, shoes, mosquito nets, bed sheets, and other things
  • Staying in places that are air-conditioned or have good window and door screens
  • Emptying out standing water (water that does not move) from things like buckets, gutters, and flowerpots (mosquitoes like to lay eggs in standing water)
  • Being extra careful between evening and morning, when the mosquitoes that spread West Nile virus are most active

Scientists can trap mosquitoes and birds, and test them for West Nile virus to see if the virus is spreading in a certain area.[27] If it is, they can do things like spray pesticides to kill mosquitoes.

Related pages[change | change source]

Other websites[change | change source]

About West Nile virus


For medical professionals

References[change | change source]

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 "West Nile virus". World Health Organization Media Centre. World Health Organization. July 2011. http://www.who.int/mediacentre/factsheets/fs354/en/. Retrieved January 29, 2016.
  2. Steinman, A.; Banet-Noach, C.; Tal, S.; Levi, O.; Simanov, L.; Perk, S.; Malkinson, M.; Shpigel, N. (2003). "West Nile Virus Infection in Crocodiles". Emerging Infectious Diseases 9 (7): 887–889. doi:10.3201/eid0907.020816. PMC 3023443. PMID 12899140.
  3. Klenk, K.; Snow, J.; Morgan, K.; Bowen, R.; Stephens, M.; Foster, F.; Gordy, P.; Beckett, S. et al. (2004). "Alligators as West Nile Virus Amplifiers". Emerging Infectious Diseases 10 (12): 2150–2155. doi:10.3201/eid1012.040264. PMC 3323409. PMID 15663852.
  4. 4.0 4.1 Chen, Chen C.; Jenkins, Emily; Epp, Tasha; Waldner, Cheryl; Curry, Philip S.; Soos, Catherine (2013-07-22). "Climate Change and West Nile Virus in a Highly Endemic Region of North America" (in en). International Journal of Environmental Research and Public Health 10 (7): 3052–3071. doi:10.3390/ijerph10073052. PMC 3734476. PMID 23880729. http://www.mdpi.com/1660-4601/10/7/3052.
  5. Murray KO, Ruktanonchai D, Hesalroad D, Fonken E, Nolan MS (November 2013). "West Nile virus, Texas, USA, 2012". Emerging Infectious Diseases 19 (11): 1836–8. doi:10.3201/eid1911.130768. PMC 3837649. PMID 24210089. http://dx.doi.org/10.3201/eid1911.130768. Retrieved 2014-12-08.
  6. Fox, M. (May 13, 2013). "2012 was deadliest year for West Nile in US, CDC says". NBC News. http://vitals.nbcnews.com/_news/2013/05/13/18232095-2012-was-deadliest-year-for-west-nile-in-us-cdc-says. Retrieved May 13, 2013.
  7. 7.0 7.1 7.2 "West Nile Virus: What You Need to Know CDC Fact Sheet". www.CDC.gov. http://www.CDC.gov/ncidod/Dvbid/westnile/WNV_factsheet.htm. Retrieved 2012-04-09.
  8. Davis LE, DeBiasi R, Goade DE, etal (Sep 2006). "West Nile virus neuroinvasive disease". Ann Neurol 60 (3): 286–300. doi:10.1002/ana.20959. PMID 16983682.
  9. Flores Anticona EM, Zainah H, Ouellette DR, Johnson LE (2012). "Two case reports of neuroinvasive west nile virus infection in the critical care unit". Case Rep Infect Dis 2012: 839458. doi:10.1155/2012/839458. PMC 3433121. PMID 22966470.
  10. Carson PJ, Konewko P, Wold KS, etal (2006). "Long-term clinical and neuropsychological outcomes of West Nile virus infection". Clin. Infect. Dis. 43 (6): 723–30. doi:10.1086/506939. PMID 16912946.
  11. 11.0 11.1 11.2 Sejvar JJ, Haddad MB, et al. 2003. "Neurologic Manifestations and Outcome of West Nile Virus Infection". Journal of the American Medical Association 290 (4): 511-515. doi:10.1001/jama.290.4.511.
  12. Mojumder, D. K., Agosto, M., Wilms, H. (March 2014). "Is initial preservation of deep tendon reflexes in West Nile Virus paralysis a good prognostic sign?". Neurology Asia 19 (1): 93–97. PMC 4229851. PMID 25400704.
  13. Montgomery SP, Chow CC, Smith SW, Marfin AA, O'Leary DR, Campbell GL (2005). "Rhabdomyolysis in patients with west nile encephalitis and meningitis". Vector-Borne and Zoonotic Diseases 5 (3): 252–7. doi:10.1089/vbz.2005.5.252. PMID 16187894.
  14. Paddock CD, Nicholson WL, Bhatnagar J, etal (June 2006). "Fatal hemorrhagic fever caused by West Nile virus in the United States". Clin. Infect. Dis. 42 (11): 1527–35. doi:10.1086/503841. PMID 16652309.
  15. Asnis DS, Conetta R, Teixeira AA, Waldman G, Sampson BA (March 2000). "The West Nile Virus outbreak of 1999 in New York: the Flushing Hospital experience". Clin. Infect. Dis. 30 (3): 413–8. doi:10.1086/313737. PMID 10722421.
  16. Smith RD, Konoplev S, DeCourten-Myers G, Brown T (February 2004). "West Nile virus encephalitis with myositis and orchitis". Hum. Pathol. 35 (2): 254–8. doi:10.1016/j.humpath.2003.09.007. PMID 14991545.
  17. Anninger WV, Lomeo MD, Dingle J, Epstein AD, Lubow M (2003). "West Nile virus-associated optic neuritis and chorioretinitis". Am. J. Ophthalmol. 136 (6): 1183–5. doi:10.1016/S0002-9394(03)00738-4. PMID 14644244.
  18. "2012 DOHMH Advisory #8: West Nile Virus" (PDF). New York City Department of Health and Mental Hygiene. June 28, 2012. http://www.nyc.gov/html/doh/downloads/pdf/cd/2012/12md08.pdf.
  19. Tyler KL, Pape J, Goody RJ, Corkill M, Kleinschmidt-DeMasters BK (February 2006). "CSF findings in 250 patients with serologically confirmed West Nile virus meningitis and encephalitis". Neurology 66 (3): 361–5. doi:10.1212/01.wnl.0000195890.70898.1f. PMID 16382032.
  20. 20.0 20.1 Hayes EB, Komar N, Nasci RS, Montgomery SP, O'Leary DR, Campbell GL (2005). "Epidemiology and transmission dynamics of West Nile virus disease". Emerging Infect. Dis. 11 (8): 1167–73. doi:10.3201/eid1108.050289a. PMC 3320478. PMID 16102302. http://www.cdc.gov/ncidod/EID/vol11no08/05-0289a.htm.
  21. Fonseca K, Prince GD, Bratvold J, etal (2005). "West Nile virus infection and conjunctive exposure". Emerging Infectious Diseases 11 (10): 1648–9. doi:10.3201/eid1110.040212. PMC 3366727. PMID 16355512.
  22. Centers for Disease Control and Prevention (CDC) (2002). "Investigation of blood transfusion recipients with West Nile virus infections". Morbidity and Mortality Weekly Report 51 (36): 823. PMID 12269472.
  23. Centers for Disease Control and Prevention (CDC) (2002). "West Nile virus infection in organ donor and transplant recipients—Georgia and Florida, 2002". Morbidity and Mortality Weekly Report 51 (35): 790. PMID 12227442.
  24. Centers for Disease Control and Prevention (CDC) (2002). "Intrauterine West Nile virus infection—New York, 2002". Morbidity and Mortality Weekly Report 51 (50): 1135–6. PMID 12537289.
  25. Centers for Disease Control and Prevention (CDC) (2002). "Possible West Nile virus transmission to an infant through breast-feeding—Michigan, 2002". Morbidity and Mortality Weekly Report 51 (39): 877–8. PMID 12375687.
  26. "West Nile Virus: Prevention & Control". CDC.gov. United States Centers for Disease Control and Prevention. November 10, 2015.
  27. Jozan, M; Evans R; McLean R; Hall R; Tangredi B; Reed L; Scott J (Fall 2003). "Detection of West Nile virus infection in birds in the United States by blocking ELISA and immunohistochemistry". Vector-Borne and Zoonotic Diseases 3 (3): 99–110. doi:10.1089/153036603768395799. PMID 14511579.