Symptoms, Diagnosis, & Treatment


No symptoms in most people. Most people (8 out of 10) infected with West Nile virus do not develop any symptoms.

Febrile illness (fever) in some people. About 1 in 5 people who are infected develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with febrile illness due to West Nile virus recover completely, but fatigue and weakness can last for weeks or months.

Serious symptoms in a few people. About 1 in 150 people who are infected develop a severe illness affecting the central nervous system such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord).

  • Symptoms of severe illness include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.
  • Severe illness can occur in people of any age; however, people over 60 years of age are at greater risk for severe illness if they are infected (1 in 50 people). People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk.
  • Recovery from severe illness might take several weeks or months. Some effects to the central nervous system might be permanent.
  • About 1 out of 10 people who develop severe illness affecting the central nervous system die.


If you think you or a family member might have West Nile virus disease, talk with your health care provider.

  • Healthcare providers diagnose West Nile virus infection based on:
    • Signs and symptoms
    • History of possible exposure to mosquitoes that can carry West Nile virus
    • Laboratory testing of blood or spinal fluid
  • Your healthcare provider can order tests to look for West Nile virus infection or other infections that can cause similar symptoms.

To learn more about testing, visit our Healthcare Providers page.


  • No vaccine or specific medicines are available for West Nile virus infection. Antibiotics do not treat viruses.
  • Rest, fluids, and over-the-counter pain medications may relieve some symptoms.
  • In severe cases, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.

To learn more about treatment, visit our Healthcare Providers page.


Most people infected with West Nile virus are believed to have lifelong immunity from getting the disease again. Some people who have weakened immune systems from certain conditions or medications might not have a strong immune response to the initial infection or their immunity may wane over time. However, most people are protected from getting West Nile virus disease again once they have had it.