West Nile fever is an illness caused by a virus. The virus is spread by mosquito bites. It often 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.

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. West Nile virus was first identified in 1937 in Uganda in eastern Africa. 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 reported in all lower 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.

West Nile fever can occur in late summer and early fall in temperate climates. 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 uncommon.

West Nile virus isn't often spread from person to person. But it can be spread in the uterus from mother to baby. The most common way it is spread is by a mosquito bite. But it may also be spread through donated organs and blood transfusions. 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.

Only about 1 in 5 people who are 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 often appear in 3 to 14 days of infection. The most common symptoms include:

• Fever
• Headache
• Body aches
• Skin rash on chest (torso)
• Swollen lymph glands
• Vomiting
• Diarrhea
• Weakness and fatigue

The symptoms of West Nile fever can seem like other health conditions. Make sure your child sees their doctor for a diagnosis.

The doctor will ask about your child's symptoms and health history. They will give your child a physical exam. Your child may also have tests to check for signs of the virus. These include:

• Blood tests to look for antibodies to the West Nile virus
• Spinal tap (lumbar puncture)
• Electroencephalogram (EEG)
• CT scan
• MRI

There is no treatment for West Nile fever other than supportive care. If your child develops West Nile encephalitis or meningitis, they may be treated in the hospital. They may need:

• I.V. (intravenous) fluids
• Breathing support with a machine (ventilator)
• Prevention of other infections, such as pneumonia or urinary tract infections
• Some I.V. treatments, such as interferon or ribavirin (depending on the severity of the child's illness)

In rare cases, the virus can affect the brain and lead to weakness, paralysis, seizures, coma, or death from:

• 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
• Confusion
• Coma
• Tremors
• Convulsions
• Muscle weakness
• Paralysis

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, picaridin, oil of lemon eucalyptus, or other EPA-registered products on your child's exposed skin before going outdoors.
• When possible, have your child wear long-sleeved shirts and long pants treated with permethrin, picaridin, DEET, or other EPA-registered insect repellants. This is important because mosquitoes may bite through thin clothing. Don't put permethrin on the skin.
• Think about 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. This can help limit the 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. Use it sparingly around the ears.
• Don't put repellent on children's hands. Children often put their hands in their mouths.
• Don't let a young child apply their own repellent.
• Don't put aerosol or pump products right on your child's face. Spray your hands first. Then rub them carefully over the face. Stay 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 goes back indoors, wash treated skin with soap and water.
• Use repellent with 30% DEET or less on children ages 2 months and older. Ask your doctor about ways to prevent mosquito bites for your child under age 2 months. Insect repellents are not advised for children under age 2 months.
• Picaridin insect repellents can be used on children over age 2 months.
• Don't use combination sunscreen–insect repellent products. This is because reapplying these 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 your child wears it again.

According to the American Academy of Pediatrics, repellents with a higher concentration of active ingredients such as DEET give longer-lasting protection:

• A product with 30% DEET gives an average of 5 hours of protection from mosquito bites.
• A product with 20% DEET gives almost 4 hours of protection from mosquito bites.
• A product with 10% DEET gives almost 2 hours of protection from mosquito bites.
• Products with 4.75% DEET and other 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 doctor if you need more information.

Contact the doctor if your child has:

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

• 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 often 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.
• It 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. But you can help prevent the spread of the virus by protecting against mosquito bites.

Tips to help you get the most from a visit to your child's doctor:

• 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 doctor 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 doctor after office hours. This is important if your child becomes ill and you have questions or need advice.