West Nile Virus

West Nile virus is a mosquito-borne virus that can cause no symptoms at all or life-threatening brain inflammation. It is the leading cause of mosquito-borne disease nationwide.

Overview

West Nile virus is a member of the flavivirus family, which includes other mosquito-borne viruses such as Dengue and Zika. The virus first appeared in the Western Hemisphere in New York City in 1999. It has since spread across the United States.

Related Terms: West Nile fever

Signs and Symptoms

Most West Nile virus infections cause no symptoms. When symptoms do occur, they range from mild to severe.

Mild symptoms include:

  • Fever
  • Body aches
  • Skin rash
  • Swollen lymph nodes
  • Weakness
  • Joint pain
  • Chills

In rare cases people who acquire West Nile virus will develop severe neuroinvasive disease.

Severe neuroinvasive symptoms include:

  • Meningitis (inflammation of the membranes surrounding the brain and spinal cord)
  • Encephalitis (brain swelling)
  • Acute flaccid paralysis
  • Ocular symptoms

Related Health Effects

If West Nile virus crosses the blood-brain barrier, it can cause life-threatening inflammation of the brain and spinal cord persistent movement disorders, thinking and memory problems, and long-term disability. West Nile Virus may also cause chronic kidney infection.

Causes and Risk Factors

West Nile virus spreads to people through the bite of an infected mosquito.

Risk factors associated with more severe West Nile virus include:

Prevention Guidance

Currently, no licensed West Nile virus vaccine exists for people. Prevention depends on avoiding mosquito bites.

To prevent mosquito bites:

  • Cover your skin. When outside, use long sleeves, pants, and socks to help block bites.
  • Use insect repellents when outside. Products containing DEET, picaridin, lemon eucalyptus, IR3535, or para-menthane-dio can be sprayed directly on your skin. Follow label instructions. Products containing permethrin can be put on clothing and outdoor gear. Don’t spray permethrin directly on your skin. Find effective bug repellents from the EPA.
  • Use a fan when sitting outside. Aim the air from a box fan at your legs when eating outside or gardening.
  • Protect your home. Use screens on open doors and windows. Repair screens if they get holes.
  • Remove breeding grounds. Drain puddles around your house where mosquitoes can lay eggs. Look for pots, buckets, pet bowls, gutters, lawn decorations, and other sites that hold water.

Diagnosis

Diagnosis for West Nile virus is based on blood and/or cerebrospinal fluid (CSF) testing.

Treatment and Management

There are no specific therapies approved for serious West Nile virus infection. Rest, fluids, and pain medicines may relieve some symptoms. People with severe illnesses may need to be hospitalized to receive supportive treatment.

Find Clinical Trials

Clinical trials uncover better ways to prevent, diagnose, treat, and understand diseases and conditions. To ensure results apply to everyone, volunteers of all ages, sexes, and backgrounds, including both healthy individuals and those with specific medical conditions, are needed. Find clinical trials on West Nile virus.

Community Support

Research Information

The National Institutes of Health (NIH) is the largest public funder of biomedical research in the world. NIH invests most of its budget in medical research seeking to enhance life and to reduce illness and disability. NIH-funded research has led to breakthroughs and new treatments helping people live longer, healthier lives, and building the research foundation that drives discovery.

NIH is funding projects on the diagnosis and treatment of West Nile virus. Researchers are working to develop simple devices for diagnosis. The goal is to develop cost-effective, rapid methods that could be performed in a doctor’s office or even at home. That would enable earlier, potentially more effective treatments.

NIH-funded researchers are evaluating several antiviral approaches against West Nile virus. These include antibodies and other compounds.

West Nile virus vaccines have been approved for use in horses. NIH supports research on a variety of approaches to develop an effective preventive vaccine for West Nile virus in people.

NIH also conducts and funds research on West Nile virus biology and viral structure. Other studies focus on how the virus causes human disease and persists in the body. Researchers are studying how the immune system responds to West Nile virus and how these responses interact to affect infection. They are also examining how West Nile virus evolves and adapts to changing environments.

NIH also supports a comprehensive vector biology research program to advance science and identify approaches to control or prevent mosquito-borne diseases, including West Nile.

Find NIH-funded research projects using NIH RePORTER, a searchable database of current and past research projects supported by NIH and other federal agencies.