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West Nile Virus
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Infections

West Nile Virus

West Nile virus is an infectious disease primarily spread by mosquito bites that can range from asymptomatic or mild illness to rare, life-threatening neurological complications.

What is West Nile Virus?

West Nile virus (WNV) is an infectious disease. It is most often spread by the bite of an infected mosquito. Most people have no symptoms, while some may develop mild symptoms. But WNV can sometimes cause serious symptoms if the virus enters your brain.

How does West Nile Virus spread?

WNV usually spreads to people through the bite of an infected mosquito. However, in rare cases, it can spread from person-to-person. This can happen through an organ transplant or blood transfusion. If you are pregnant you can spread WNV to your fetus during pregnancy or delivery. And after delivery, it can spread to the baby during breastfeeding.

Who is more likely to develop West Nile Virus?

Anyone could be bitten by an infected mosquito and get WNV. But certain people are at higher risk for more serious illness if they get a WNV infection. They include people who:

  • Are over age 60
  • Have certain medical conditions, such as cancer, diabetes, high blood pressure, or kidney disease
  • Had an organ transplant

What are the symptoms of West Nile Virus?

Symptoms can be mild to severe. But most people have no symptoms or mild symptoms.

Mild symptoms of WNV can include:

  • Fever
  • Headache
  • Body aches
  • Vomiting
  • Diarrhea
  • Skin rash

These symptoms usually go away on their own within a few days to several weeks. But some people will have weakness or fatigue that lasts for weeks or months.

Although rare, if West Nile virus enters your brain, it can be life-threatening. It may cause inflammation of the brain (encephalitis) or inflammation of the tissue that surrounds the brain and spinal cord (meningitis).

Serious symptoms of WNV can include:

  • High fever
  • Headache
  • Neck stiffness
  • Numbness
  • Coma
  • Muscle weakness
  • Vision loss

How is West Nile Virus diagnosed?

To find out if you have WNV, your health care provider:

  • Will do a physical exam
  • Will take your medical history, including asking about your symptoms
  • May order blood tests

What are the treatments for West Nile Virus?

There are no specific vaccines or treatments for human WNV disease. But rest, fluids, and over-the-counter pain medicines may relieve some symptoms. You may need to be hospitalized if you have serious symptoms.

Can West Nile Virus be prevented?

There are no vaccines or medicines to prevent WNV. The best way to avoid WNV is to help prevent mosquito bites:

  • Wear insect repellent with DEET or another U.S. Environmental Protection Agency (EPA)-registered insect repellent. Make sure to follow the instructions for using the repellent.
  • Wear long-sleeved shirts and pants if you're outside.
  • Get rid of mosquito breeding sites by emptying standing water from flowerpots, buckets, or barrels.
  • Stay indoors between dusk and dawn, when mosquitoes are most active.
  • Use screens on windows to keep mosquitoes out.

Centers for Disease Control and Prevention (CDC)

Frequently Asked Questions

Currently, there is no specific antiviral treatment or vaccine for West Nile Virus in humans. Treatment is supportive, focusing on managing symptoms such as hydration, rest, and pain relief with acetaminophen. It is important to avoid aspirin or ibuprofen if there is any concern about bleeding risks, though this is generally a precaution for severe cases. Recovery can take weeks or months, and some individuals may experience long-term fatigue or muscle weakness.
It is difficult to distinguish West Nile Virus from other summer fevers like dengue or chikungunya based on symptoms alone, as they all present with fever, headache, and body aches. However, West Nile Virus is often associated with a skin rash and swollen lymph nodes. If you live in an area with active mosquito-borne disease transmission and develop a high fever that persists for more than three days, you should consult a healthcare provider. A blood test is the only way to confirm a West Nile Virus infection, as symptoms overlap with many other viral illnesses.
Neurological complications, such as encephalitis or meningitis, are rare but serious. Warning signs include severe or persistent headache, high fever, confusion, disorientation, loss of consciousness, convulsions, muscle weakness, tremors, and loss of coordination. If you or someone else experiences these symptoms after a mosquito bite or during peak mosquito season, it is a medical emergency requiring immediate hospitalization for supportive care and monitoring.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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