KidsMD Health Topics

West Nile Virus

  • Avoiding mosquito and insect bites ‎

    Learn more about insect bites in the article More bugs and bites? Protect your child from ticks and mosquitoes this season, posted on Thriving, Boston Children’s Hospital’s pediatric health blog.

    Infectious Diseases
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  • In-Depth


    What causes West Nile Virus?

    West Nile virus is a mosquito borne illness, which means that it is caused by the bite of an infected mosquito. There is no evidence that suggests that the disease is spread by any other insect besides mosquitoes—and it can’t spread between people. While animals can become infected, they can’t spread the infection either.

    In a few cases, West Nile virus has been spread through blood transfusions. However, the risk of developing the infection this way is very low due to routine screening of donated blood. There have also been a few reports of pregnant women passing on West Nile virus to their fetuses.

    Risk factors

    The overall risk of becoming infected with West Nile virus can depend on:

    • Time spent outdoors: People who spend a lot of time working or playing outdoors are more at risk of getting West Nile virus because they have a greater chance of being bitten by an infected mosquito. 
    • Time of year and day: In North America, cases of West Nile virus are more frequent between from July through early September, when the mosquito population is at its peak. Mosquitoes are also most active during dusk and dawn, especially in damp or heavily wooded areas.
    • Geographic region: Cases of West Nile virus have been reported in most parts of the United States, but the highest rates are seen in Western and Midwestern states.


    What are the symptoms of West Nile Virus?

    Most children with West Nile virus do not show any signs of illness. In 20 percent of cases, the symptoms of West Nile virus in children are “flu-like” and include:

    • Fever
    • Headache
    • Body aches
    • Tiredness
    • Joint pain
    • Swollen lymph glands
    • Skin rash 

    Since West Nile-related encephalitis is caused by a virus, symptoms may appear along with signs of an upper respiratory infection (cold, sore throat), or gastrointestinal problems (diarrhea, nausea, vomiting or rash).

    In less than 1 percent of cases, children develop a severe infection that causes swelling of the brain (encephalitis), which can cause brain damage. The symptoms of encephalitis depend on the part of the brain that is inflamed, the degree of inflammation and the person’s age and overall health (adults age 50 and older and people with a weakened immune system due to cancer treatments or organ transplantation are greater at risk).

    Some of the most common symptoms of encephalitis include: 

    • High fever
    • Severe headache
    • Neck stiffness
    • Convulsions
    • Nausea/vomiting
    • Confusion (disorientation)
    • Tremors

    When to see a doctor

    Symptoms of West Nile virus usually occur anywhere from three days to two weeks after getting bitten by an infected mosquito. Although mild cases of West Nile virus can be treated at home, encephalitis needs to be treated by a doctor. See your doctor if you notice any concerning changes in your child’s behavior. Diagnosing West Nile virus early can help speed up recovery and prevent any serious complications from occurring. 

  • Tests


    How is West Nile Virus diagnosed?

    To determine a child’s risk of having a West Nile virus infection, the doctor will observe his symptoms and ask about his exposure to mosquitos.

    A diagnosis of West Nile virus can be confirmed using:

    • Blood tests. Someone who is infected with West Nile virus will have an increased level of antibodies against the disease. Antibodies are proteins produced by the immune system that attack foreign substances such as viruses, bacteria and other harmful organisms. Elevated levels of antibodies signal that your immune system is fighting the infection by producing a surplus of antibodies.  

    If encephalitis is suspected, the following procedures may be used as to confirm the diagnosis:

    • Lumbar puncture (spinal tap): During a spinal tap, a special needle is placed into the lower back and a small amount of cerebral spinal fluid is removed. This fluid sample is sent for testing to determine if a child has West Nile virus or other problems.
    • Electroencephalogram (EEG) An EEG works by recording the brain's continuous electrical activity using stickers attached to the scalp that measure electrical activity. The purpose of an EEG is to see if your child is having small brain seizures that are not visible from the outside.

  • Treatment options 

    How is West Nile Virus treated?

    There is currently no vaccine for human the West Nile disease. Antibiotics are not an effective course of treatment since they only fight bacterial infections, and the West Nile disease is caused by a virus. However, over-the-counter (OTC) medications, such as acetaminophen, can be used to relieve symptoms such as fever and headaches.

    There are also supportive therapies for children who have developed encephalitisas a result of West Nile virus infection. Except for very mild cases, most children with encephalitis will need to be treated at a hospital. Doctors will carefully monitor the child's blood pressure, heart rate and breathing to prevent further brain inflammation from occurring. Medications a child might receive include corticosteroids to reduce brain swelling and anticonvulsants to prevent or control seizures.

    With the right care, most children with encephalitis make a full recovery.


    How can I prevent West Nile Virus? 

    Avoiding mosquito bites is the easiest and most effective way to prevent West Nile virus in children. The steps you can take to protect your child include:

    • Wear long-sleeved shirts and pants that cover your skin, especially in the evenings when there are more mosquitoes around.
    • Don't hang out near puddles or other pools of standing water like gutters or wading pools—they are common breeding grounds for mosquitoes. 
    • Get rid of mosquito breeding sites by emptying standing water in flower pots, buckets, old tires, etc.If you find a dead bird, don't touch it with your bare hands or try to move it. Let your parents know so they can contact your local health department right away

    Using insect repellent is the easiest and most effective way to avoid mosquito bites. The American Academy of Pediatrics (AAP) recommends DEET (usually listed on labels as N, N-diethyl-m-toluamide) as the best repellant against ticks and mosquitos.

    Products with up to 30 percent DEET are safe to use on children 2 months of age and older, although experts from the AAP do not recommend using it in infants less than 2 months old. DEET should also not be applied to the face or hands of young children.

    Applying repellants

    The Enviorenmental Protection Agency (EPA) offers these additional tips for applying insect repellants: 

    • Don't use insect repellent on skin that is already covered by clothing.
    • Do not apply repellant directly onto a child's face. Instead, spray the repellent in your hands first and then gently rub it on, avoiding the eyes and mouth. 
    • Avoid spraying repellent on your child's hands, since she could put them in her mouth or eyes.
    • Wash repellent off once you get back indoors.
    • Don't use repellent on areas of the skin that are irritated or cut.
    • Stop using a repellent if it gives you a rash or other skin reaction, wash it off and call the doctor.
    Bug spray: What parents should know 

    Claire McCarthy, MD, a pediatrician at Boston Children's Hospital, talks about the most effective insect repellants for children in her articleKids and bug spray--what you need to know, posted on


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