Overview

West Nile fever is an illness caused by a virus. The virus is spread by mosquito bites. West Nile fever in people is rare. It usually causes mild, flu-like symptoms. In rare cases, it can cause life-threatening illness of the brain and lining covering the brain and spinal cord.

Causes

The illness is caused by West Nile virus. The West Nile virus belongs to a group of viruses known as flaviviruses. These viruses are commonly found in Africa, West Asia, Australia, Europe, and the Middle East. Flaviviruses are spread by insects, most often mosquitoes. Other examples of flaviviruses include yellow fever, Japanese encephalitis, dengue virus, and St. Louis encephalitis virus. West Nile virus is closely related to the St. Louis encephalitis virus.

The West Nile virus can infect humans, birds, mosquitoes, horses, and some other mammals. In 1999, the virus occurred in the Western hemisphere for the first time. The first cases were reported in New York City. Since then, West Nile virus has been considered an emerging infectious disease in the U.S. It has spread down the East Coast and to many Southern and Midwestern states. It has been discovered in 48 states in the U.S.

West Nile virus is spread to humans through the bite of an infected female mosquito. The mosquitoes get the virus by biting infected birds. Crows and jays are the most common birds with the virus. But at least 110 other bird species also have been shown to have the virus.

Risk Factors

West Nile fever can occur in late summer and early fall in temperate zones. It can occur year-round in warmer climates. People are most at risk of infection from June to September. But West Nile fever in people is rare.

West Nile virus isn't usually spread from person to person. But some people may get the virus through donated organs and blood transfusion. The FDA notes that the risk for West Nile from blood is much lower than the risks of skipping a needed organ transplant or blood transfusion.

Symptoms

Only about 1 in 5 people who become infected with the virus will develop West Nile fever. Most children with West Nile fever have only mild, flu-like symptoms that last a few days. Symptoms usually appear within 3 to 14 days of infection. The most common symptoms include:

  • Fever
  • Headache
  • Body aches
  • Skin rash on torso
  • Swollen lymph glands

In rare cases, the virus can affect the brain and lead to:

  • West Nile encephalitis. This is inflammation of the brain caused by the virus.
  • West Nile meningitis. This is inflammation of the lining of the brain and spinal cord caused by the virus.
  • West Nile meningoencephalitis. This is inflammation of the brain and the lining of the brain and spinal cord caused by the virus.

These conditions can cause symptoms such as:

  • Headache
  • High fever
  • Neck stiffness
  • Confusion
  • Extreme tiredness
  • Disorientation
  • Coma
  • Tremors
  • Convulsions
  • Muscle weakness
  • Paralysis

The symptoms of West Nile fever can be like other health conditions. Make sure your child sees his or her healthcare provider for a diagnosis.

Diagnosis

The healthcare provider will ask about your child’s symptoms and health history. He or she will give your child a physical exam. Your child may also have tests to check for signs of the virus. These include:

  • Blood tests
  • Spinal tap (lumbar puncture)
  • Electroencephalogram (EEG)
  • CT scan
  • MRI

Treatment

There is no treatment for West Nile fever. If a child develops West Nile encephalitis or meningitis, your child may be treated in the hospital. He or she may need:

  • Intravenous (IV) fluids
  • Breathing support with a ventilator
  • Prevention of other infections, such as pneumonia or urinary tract infections

Complications

In rare cases, the virus can affect the brain and lead to:

  • West Nile encephalitis. This is inflammation of the brain caused by the virus.
  • West Nile meningitis. This is inflammation of the lining of the brain and spinal cord caused by the virus.
  • West Nile meningoencephalitis. This is inflammation of the brain and the lining of the brain and spinal cord caused by the virus.

Prevention

No vaccine is available to prevent West Nile fever. But you can help prevent the spread of the virus by protecting against mosquito bites. The CDC recommends the following steps to prevent mosquito bites:

  • Use insect repellent containing DEET on your child’s exposed skin before going outdoors.
  • When possible, have your child wear long-sleeved shirts and long pants treated permethrin or DEET. This is important because mosquitoes may bite through thin clothing. Don't put permethrin on the skin.
  • Consider keeping your child indoors at dawn, dusk, and in the early evening. These are peak hours for mosquito bites, especially mosquitoes that carry the West Nile virus.
  • Remove standing water around your home to limit the number of places available for mosquitoes to lay their eggs.

Tips for safely applying insect repellent include:

  • When using repellent on a child, put it on your own hands and then rub them on your child.
  • Don't put the repellent near your child's eyes or mouth and use the repellent sparingly around the ears.
  • Don't put repellent on children's hands because children tend to put their hands in their mouths.
  • Don't allow a young child to apply his or her own insect repellent.
  • Don’t put aerosol or pump products directly on your child's face. Spray your hands and then rub them carefully over the face, staying away from the eyes and mouth.
  • Don’t spray aerosol or pump products in enclosed spaces.
  • Don’t put repellent on cuts, wounds, or irritated skin.
  • Use enough repellent to cover exposed skin or clothing.
  • You don't need a lot of repellent to get protection.
  • Reapply if your child sweats heavily or after swimming.
  • After your child returns indoors, wash treated skin with soap and water.
  • Use repellent with 30% DEET or less on children ages 2 to 12. Ask your healthcare provider about your child under age 2.
  • Don't use combination sunscreen-insect repellent products. This is because reapplying often enough to prevent sunburn will expose your child to too much DEET. 
  • Don't put repellent on skin under clothing. If repellent is put on clothing, wash treated clothing before wearing again.

According to the CDC, repellents containing a higher concentration of active ingredient such as DEET give longer-lasting protection.

  • A product containing 23.8% DEET gives an average of 5 hours of protection from mosquito bites.
  • A product containing 20% DEET gives almost 4 hours of protection from mosquito bites.
  • A product with 6.65% DEET gives almost 2 hours of protection from mosquito bites.
  • Products with 4.75% DEET and products made from citronella, eucalyptus, or soybean oil are able to give about 1.5 hours of protection from mosquito bites.

Talk with your child’s healthcare provider if you need more information.

When to Call a Healthcare Provider

Call the healthcare provider if your child has:

  • Symptoms that don’t get better, or get worse
  • New symptoms

Key Points

  • West Nile fever is an illness caused by a virus. The virus is spread by mosquito bites.
  • West Nile fever in people is rare. It usually causes mild, flu-like symptoms.
  • In rare cases, it can cause life-threatening illness of the brain and lining covering the brain and spinal cord.
  • West Nile fever can occur in late summer and early fall in temperate zones. It can occur year-round in warmer climates. People are most at risk of infection from June to September.
  • Only about 1 in 5 people who become infected with the virus will develop West Nile fever. Most children with West Nile fever have only mild, flu-like symptoms that last a few days.
  • No vaccine is available to prevent West Nile fever. But you can help prevent the spread of the virus by protecting against mosquito bites.

Next Steps

Tips to help you get the most from a visit to your child’s healthcare provider:

  • Know the reason for the visit and what you want to happen.
  • Before your visit, write down questions you want answered.
  • At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you for your child.
  • Know why a new medicine or treatment is prescribed and how it will help your child. Also know what the side effects are.
  • Ask if your child’s condition can be treated in other ways.
  • Know why a test or procedure is recommended and what the results could mean.
  • Know what to expect if your child does not take the medicine or have the test or procedure.
  • If your child has a follow-up appointment, write down the date, time, and purpose for that visit.
  • Know how you can contact your child’s provider after office hours. This is important if your child becomes ill and you have questions or need advice.