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West Nile Virus

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Definition

West Nile virus (WNV) is an infection that is most commonly spread by being bitten by an infected mosquito. In rare cases, WNV can lead to serious complications and even death. This infection is found worldwide and may occur during late summer and early fall in the United States.

Causes

The most common cause is being bitten by a mosquito that is infected with WNV. There are other, rarer causes, such having a blood transfusion with infected blood.

Risk Factors

The greatest risk factors for WNV are spending time in areas where mosquitoes are present and not using insect repellent.
Risk factors for having complications from WNV include:
  • Being over 50 years old
  • Having a condition that affects your immune system
Mosquito Bite
Mosquito bite
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Symptoms

Most people with WNV have no symptoms. About 20% of the people who become infected with WNV develop flu-like symptoms, for example:
  • Fever and chills
  • Headache
  • Muscle pain
  • Nausea and vomiting
  • Diarrhea
  • Rash
  • Swollen lymph nodes
  • Eye inflammation (conjunctivitis)
Symptoms may appear within 2-15 days and can last from a few days to several weeks.
A small percentage of people with WNV will develop serious, neurological symptoms that affect the brain and spinal cord. These symptoms may include:
  • High fever
  • Headache
  • Stiff neck
  • Disorientation
  • Stupor
  • Tremors
  • Vision loss
  • Severe muscle weakness
  • Paralysis
  • Coma
These serious symptoms can lead to death.

Diagnosis

In addition to taking your medical history and doing a physical exam, your doctor will ask you:
  • What kind of symptoms you are experiencing
  • Where you have been living or traveling to
  • Whether you have been exposed to mosquitoes
A blood test is commonly used to confirm the diagnosis of WNV. Depending on the symptoms that you have, your doctor may order other tests, such as:

Treatment

Treatment for WNV focuses on supportive care. Depending on your symptoms your doctor may recommend:
  • Pain relieving medicine
  • Medicine to reduce nausea and vomiting
If you are dehydrated, you may need to drink an oral rehydration solution or have fluid delivered intravenously through a vein in your arm.
Treatment for severe symptoms may include:

Prevention

The best preventive measure is to avoid mosquito bites. You can do this by:
  • Not going outdoors at dawn or dusk
  • Wearing long pants and long-sleeve shirts when outdoors
  • Using an insect repellent with DEET
  • Repairing screens to prevent mosquitoes from entering the house
  • Removing standing water (eg, bird baths, clogged gutters) to prevent mosquito breeding
Mosquitoes contract WNV by biting infected birds. If you see a dead bird, call the public health department. Do not touch the dead bird unless you are wearing disposable gloves.

RESOURCES

Centers for Disease Control and Prevention http://www.cdc.gov

National Library of Medicine http://www.nlm.nih.gov/

CANADIAN RESOURCES

Health Canada http://www.hc-sc.gc.ca/index%5Fe.html/

Healthy U http://www.healthyalberta.com/

References

Glass JD, Samuels O, Rich MM. Poliomyelitis due to West Nile virus [letter]. N Engl J Med. 2002;347:1280-1281.

Petersen LR, Marfin AA. West Nile virus: a primer for the clinician. Ann Intern Med. 2002;137:173-179.

Petersen LR, Roehrig JT, Hughes JM. West Nile virus encephalitis. N Engl J Med. 2002;347:1225-1226.

Quick lesson about West Nile infection. EBSCO Nursing Reference Center website. Available at: http://www.ebscohost.com/pointOfCare/nrc-about. Updated September 7, 2012. Accessed September 24, 2012.

West Nile virus infection. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed/. Updated September 13, 2012. Accessed September 24, 2012.

West Nile virus: what you need to know. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/ncidod/dvbid/westnile/wnv%5FfactSheet.htm. Updated September 12, 2012. Accessed September 24, 2012.

Revision Information

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

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