Key points
- West Nile virus can result in mild illness with flu-like symptoms or severe illness that affects the central nervous system or results in hospitalization or death.
- There is no treatment for West Nile virus disease (West Nile).
- Rest, fluids, and pain medications may relieve symptoms.
Symptoms
Symptoms usually start 2-6 days after being bitten by an infected mosquito but can start anywhere from 2-14 days. It may take longer for symptoms to start for people with a weakened immune system.
No symptoms in most people
Most people (80%) infected with West Nile virus do not develop symptoms.
Mild illness in some people
About 20% of people who are infected develop flu-like symptoms, such as a fever with headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with mild illness due to West Nile virus recover completely, but fatigue and weakness can last for weeks or months.
Severe illness in a few people
When to see a doctor
Less than 1% of people infected develop severe illness that affects the central nervous system, requires hospitalization, or results in death.
- Central nervous system infection can cause inflammation of the brain (encephalitis) and the membranes around the brain and spinal cord (meningitis).
- Symptoms of severe illness can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, and paralysis.
- Recovery from severe illness can take several weeks or months. Some effects might be permanent.
- About 10% of people who develop severe illness affecting the central nervous system die.
Risk factors
Risk of infection
Anyone who lives in or travels to an area where West Nile virus circulates is at risk of infection. All states in the contiguous United States have reported cases of West Nile.
Risk of severe illness
Anyone can develop mild or severe illness if infected with West Nile virus. However, some people are at higher risk of severe illness:
- The risk of severe illness increases with age. For example, people 65 and older are three times as likely to develop neurologic illness than people younger than 65.
- People with certain chronic medical conditions like cancer, diabetes, high blood pressure (hypertension), or kidney disease
- People with a weakened immune system, including those who take certain medications used to treat cancers, autoimmune diseases, and inflammatory conditions or prevent rejection of transplanted organs
Diagnosis
If you think you or a family member might have West Nile, talk with your healthcare provider.
- Healthcare providers diagnose West Nile virus infection based on:
- Signs and symptoms
- History of possible exposure to mosquitoes that can spread West Nile virus
- Laboratory testing of blood or spinal fluid
- Healthcare providers can order tests to look for West Nile virus infection or other infections that can cause similar symptoms.
Treatment
No medicines are available to treat West Nile. Antibiotics do not treat viral infections.
Mild illness
People with mild illness can often manage symptoms by:
- Taking over-the-counter medication like acetaminophen for fever, pain, and headaches. Avoid ibuprofen or other non-steroidal anti-inflammatory drugs (NSAIDs) if you live in an area with dengue, which is also spread by mosquitoes.
- Staying hydrated
- Resting
Severe illness
People with severe illness often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.
Healthcare providers, see Treatment and Prevention of West Nile Virus Disease.