What Is West Nile Virus?
West Nile virus (WNV) is a potentially serious illness. Experts believe WNV is now established as a seasonal epidemic in North America that flares up in the summer and continues into the fall. This fact sheet contains important information that can help you recognize and prevent West Nile virus.
What Are the Symptoms of WNV?
WNV affects the central nervous system. Symptoms vary.
- No Symptoms in Most People. Approximately 80 percent of people who are infected with WNV will not show any symptoms at all.
- Mild Symptoms in Some People. Up to 20 percent of the people who become infected will display mild symptoms, including fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms typically last a few days.
- Serious Symptoms in a Few People. About one in 150 people infected with WNV will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent.
- In very rare cases animals and persons have died as a result of thie complications this illness causes.
How Does It Spread?
- Infected Mosquitoes. Generally, WNV is spread by the bite of an infected mosquito. Mosquitoes are WNV carriers that become infected when they feed on infected birds. Infected mosquitoes can then spread WNV to humans and other animals when they bite.
- Transfusions, Transplants, and Mother-to-Child. In a very small number of cases, WNV also has spread through blood transfusions, organ transplants, breastfeeding and even during pregnancy from mother to baby.
- Not through touching. WNV is not spread through casual contact such as touching or kissing a person with the virus. How Soon Do Infected People Get Sick?
People typically develop symptoms between 3 and 14 days after they are bitten by the infected mosquito.
How Is WNV Infection Treated?
There is no specific treatment for WNV infection. In cases with mild symptoms, people experience symptoms such as fever and aches that pass on their own. In more severe cases, people usually need to go to the hospital where they can receive supportive treatment including intravenous fluids, help with breathing and nursing care.
What Should I Do if I Think I Have WNV?
Mild WNV illness improves on its own, and people do not necessarily need to seek medical attention for this infection. If you develop symptoms of severe WNV illness, such as unusually severe headaches or confusion, seek medical attention immediately. Severe WNV illness usually requires hospitalization.
Pregnant women and nursing mothers are encouraged to talk to their doctor if they develop symptoms that could be WNV.
What Is the Risk of Catching WNV?
For most, risk is low. Less than 1 percent of people who are bitten by mosquitoes develop any symptoms of the disease and relatively few mosquitoes actually carry WNV.
Greater risk for those outdoors a lot. People who spend a lot of time outdoors are more likely to be bitten by an infected mosquito. They should take special care to avoid mosquito bites.
People over 50 can get sicker. People over the age of 50 are more likely to develop serious symptoms of WNV if they do get sick and should take special care to avoid mosquito bites.
Risk through medical procedures is low. The risk of getting WNV through blood transfusions and organ transplants is very small, and should not prevent people who need surgery from having it. If you have concerns, talk to your doctor before surgery.
Pregnancy and nursing do not increase risk of becoming infected with WNV.
What Can I Do to Prevent WNV?
The easiest and best way to avoid WNV is to prevent mosquito bites.
- When you are outdoors, use insect repellents containing DEET (N, N-diethyl-meta-toluamide). Follow the directions on the package. **Caution**
- Many mosquitoes are most active at dusk and dawn. Consider staying indoors during these times or use insect repellent and wear long sleeves and pants. Light-colored clothing can help you see mosquitoes that land on you.
- Make sure you have good screens on your windows and doors to keep mosquitoes out.
- Get rid of mosquito breeding sites by emptying standing water from flower pots, buckets and barrels. Change the water in pet dishes and replace the water in bird baths weekly. Drill drainage holes in tire swings so water drains out. Keep children’s wading pools empty and on their sides when they aren’t being used.
What Else Should I Know?
If you find a dead bird: Don’t handle the body with your bare hands. Contact your local health department for instructions on reporting and disposing of the body.
For more information, visit www.cdc.gov/westnile, or call the CDC public response hotline
at (888) 246‑2675 (English), (888) 246‑2857 (Español), or (866) 874‑2646 (TTY)