West Nile virus (WNV) is an infection caused by a virus that you can get from a mosquito bite. Most of the time the illness is mild, but sometimes it can cause inflammation of the brain (encephalitis) or inflammation of the membranes that cover the brain and spinal cord (meningitis). The risk of severe infection is greatest for people who are over 70 years old or who have a weakened immune system.
What is the cause?
Wild and domestic birds, mainly crows, carry the West Nile virus. Mosquitoes get infected when they bite infected birds. The infected mosquito can then pass the virus to you when it bites you.
The virus does not spread directly from an infected bird to humans, or from person to person. However, WNV can be spread by contact with infected blood, for example, through blood transfusion, organ transplant, or the sharing of needles or syringes contaminated with blood. WNV may also be spread from a mother to her unborn baby. The virus might also be transmitted through breast milk. However, the risk of spread of the virus to the baby is believed to be very low.
The risk of West Nile virus is seasonal in the northern states of the US and usually starts in the spring. The peak time for infection is mid to late August. In milder southern climates, the risk for infection is year-round.
What are the symptoms?
Often there are no symptoms. Children are more likely to have symptoms than adults. When symptoms do occur, they usually start 3 to 14 days after a mosquito bite. They are usually mild and last a few days. Symptoms may include:
Nausea or vomiting
When WNV affects the brain, symptoms may include:
Tremors, like a shaking of your hands that you cannot control
Inability to move your body (paralysis)
How is it diagnosed?
Your healthcare provider will ask about your symptoms and medical history and examine you. Tests may include:
Lumbar puncture, also called a spinal tap, which uses a needle to get a sample of fluid from the area around the spinal cord to test for meningitis
EEG, a test that measures the electrical activity of the brain
CT scan, which uses X-rays and a computer to show detailed pictures of the brain
MRI, which uses a strong magnetic field and radio waves to show detailed pictures of the brain
How is it treated?
There is no medicine that cures West Nile virus. If your symptoms are mild, they will usually go away on their own. In most cases you can care for yourself at home. If you have a serious infection, you may need to stay at the hospital. You may be given IV fluids, pain relievers, or other treatments.
Most people infected with WNV, including nearly all children, donâ€™t get seriously ill, and they recover fully. Symptoms usually last 3 to 6 days, but they can last as long as several weeks or months.
If you have a serious infection, you may be ill for weeks or months. In the most serious cases, the nervous system or brain may be injured.
How can I take care of myself?
Follow the full course of treatment prescribed by your healthcare provider. In addition:
Take acetaminophen or an anti-inflammatory medicine, such as ibuprofen, for fever, headache, or muscle aches. Read the label and take as directed. Unless recommended by your healthcare provider, you should not take these medicines for more than 10 days.
Nonsteroidal anti-inflammatory medicines (NSAIDs), such as ibuprofen, naproxen, and aspirin, may cause stomach bleeding and other problems. These risks increase with age.
Acetaminophen may cause liver damage or other problems. Unless recommended by your provider, don’t take more than 3000 milligrams (mg) in 24 hours. To make sure you donâ€™t take too much, check other medicines you take to see if they also contain acetaminophen. Ask your provider if you need to avoid drinking alcohol while taking this medicine.
Ask your provider:
How and when you will hear your test results
How long it will take to recover
If there are activities you should avoid and when you can return to your normal activities
How to take care of yourself at home
What symptoms or problems you should watch for and what to do if you have them
Make sure you know when you should come back for a checkup.
If you are older or live alone, you may need someone to check on you at least daily to make sure you donâ€™t start having serious symptoms, such as confusion or coma.
How can I help prevent West Nile virus?
Take these precautions to avoid mosquito bites:
Stay indoors at dawn, dusk, and in the early evening, when mosquitoes are most likely to be around.
Wear long pants and long-sleeved shirts, especially from dusk to dawn. This is the time when you are most likely to get bitten.
Use an insect repellent whenever you are outdoors. Don’t use more repellent than recommended in the package directions. Don’t put repellent on open wounds or rashes. Donâ€™t put it near your eyes or mouth. When using sprays for the skin, donâ€™t spray the repellent directly on your face. Spray the repellent on your hands first and then put it on your face. Then wash the spray off your hands.
Adults should use repellent products with no more than 35% DEET. Children older than 2 months can use repellents with no more than 30% DEET. DEET should be applied just once a day. Wash it off your body when you go back indoors.
Picaridin may irritate the skin less than DEET and appears to be just as effective.
Spray clothes with repellents because mosquitoes may bite through thin clothing. Products containing permethrin are recommended for use on clothing, shoes, bed nets, and camping gear. Permethrin-treated clothing repels and kills ticks, mosquitoes, and other insects and can keep working after laundering. Permethrin should be reapplied to clothing according to the instructions on the product label. Some commercial products are available pretreated with permethrin. Permethrin does not work as a repellent when it is put on the skin.
In some studies, oil of lemon eucalyptus, a plant-based repellent, provided as much protection as repellents with low concentrations of DEET, but it hasn’t been as well tested as DEET. Oil of lemon eucalyptus should not be used on children under age 3.
Install or repair window and door screens so it is harder for mosquitoes to get indoors.
Mosquitoes lay eggs in water. To reduce mosquito breeding, drain standing water. Routinely empty water from flowerpots, pet bowls, clogged rain gutters, swimming pool covers, buckets, barrels, cans, and other items that collect water.
Developed by RelayHealth.
Adult Advisor 2015.1 published by RelayHealth. Last modified: 2014-10-21 Last reviewed: 2014-06-02
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.