West Nile Virus
Since 1999, more than 30,000 people in the United States have been reported as getting sick with West Nile virus. Infected mosquitoes spread West Nile virus (WNV) that can cause serious, life altering disease.
West Nile Virus: What You Need To Know
CDC Fact Sheet
Download PDF version formatted for print [PDF - 2 pages]
What Is West Nile Virus?
West Nile virus (WNV) is a potentially serious illness. Experts believe WNV is 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 Can I Do to Prevent WNV?
New! Prevention measures consist of community-based mosquito control programs that are able to reduce vector populations, personal protection measures to reduce the likelihood of being bitten by infected mosquitoes, and the underlying surveillance programs that characterize spatial/temporal patterns in risk that allow health and vector control agencies to target their interventions and resources.
The easiest and best way to avoid WNV is to prevent mosquito bites.
- When you are outdoors, use insect repellent containing an EPA-registered active ingredient. Follow the directions on the package.
- Many mosquitoes are most active at dusk and dawn. Be sure to use insect repellent and wear long sleeves and pants at these times or consider staying indoors during these hours.
- 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 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 Are the Symptoms of WNV?
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.
Milder Symptoms in Some People. Up to 20 percent of the people who become infected have symptoms such as fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for as short as a few days, though even healthy people have become sick for several weeks.
- No Symptoms in Most People. Approximately 80 percent of people (about 4 out of 5) who are infected with WNV will not show any symptoms at all.
How Does West Nile Virus Spread?
Infected Mosquitoes. Most often, WNV is spread by the bite of an infected mosquito. Mosquitoes 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 been 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.
|An enlarged view of a Culex quinquefasciatus mosquito larva. The C. quinquefasciatus mosquito is known as one of the many arthropodal vectors responsible for spreading the arboviral encephalitis, West Nile virus (WNV) to human beings through their bite when obtaining a blood meal. Source: CDC; Credit: Harry Weinburgh.|
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 milder symptoms, people experience symptoms such as fever and aches that pass on their own, although even healthy people have become sick for several weeks. 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?
Milder WNV illness improves on its own, and people do not necessarily need to seek medical attention for this infection though they may choose to do so. 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 Getting Sick from WNV?
People over 50 at higher risk to get severe illness. 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.
Being outside means you're at risk. The more time you're outdoors, the more time you could be bitten by an infected mosquito. Pay attention to avoiding mosquito bites if you spend a lot of time outside, either working or playing.
Risk through medical procedures is very low. All donated blood is checked for WNV before being used. 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.
Pregnancy and nursing do not increase risk of becoming infected with WNV.
The risk that WNV may present to a fetus or an infant infected through breastmilk is still being evaluated. Talk with your care provider if you have concerns.
What Is the CDC Doing About WNV?
CDC is working with state and local health departments and other government agencies, as well as private industry, to prepare for and prevent new cases of WNV.
Some things CDC does with respect to WNV include:
- Manage and maintain ArboNET, a nation-wide electronic surveillance system where states share information about WNV and other arboviral diseases;
- Support states develop and carry out improved mosquito prevention and control programs;
- Develop better, faster tests to detect and diagnose WNV;
- Prepare updated prevention and surveillance information for the media, the public, and health professionals; and
- Work with partners on the development of vaccines.
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. They may tell you to dispose of the bird after they log your report.
For more information call the CDC public response hotline
at (888) 246-2675 (English), (888) 246-2857 (Español), or (866) 874-2646 (TTY)