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West Nile virus is an illness that mainly affects birds. But mosquitoes can spread it to people and other animals. Not all mosquitoes carry the virus (germ) that causes West Nile, and most people who are infected never get sick. Older adults and people with weakened immune systems are more likely to have mild to severe symptoms. There is no vaccine for West Nile virus, so the best way to prevent infection is to avoid mosquito bites.
Mosquito bites: Most often, West Nile virus is spread by mosquitoes. When a mosquito bites a sick bird, the virus settles in the mosquito’s saliva. It can then spread easily to the next person or animal the mosquito bites.
Other types of spread: Mosquitoes cause most cases of West Nile virus. But a few people have gotten the virus from a transplanted organ or from the blood of an infected donor. And a few women have passed the virus to their babies in the womb. If you have concerns, talk to your doctor.
Most people with West Nile virus have no symptoms and never know they’ve been infected. Others have a mild illness called West Nile fever that lasts just a few days. West Nile fever seems like the flu, with symptoms that may include:
In some cases, West Nile virus leads to serious problems, such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes and fluid around the brain and spinal cord).
If West Nile is suspected, a small sample of blood or cerebrospinal fluid (the fluid that protects the brain and spinal cord) is taken. The sample is sent to a laboratory and tested for the West Nile virus.
There is no medication for West Nile virus, and most people recover fully without treatment. When symptoms are severe, hospital care may be needed. In some cases, severe illness can cause lasting problems.
The best way to prevent infection is to avoid mosquito bites. To do this:
If possible, stay indoors at dusk and dawn when mosquitoes are most active.
During mosquito season, wear socks and shoes, long-sleeved shirts, and long pants. Loose-fitting, light-colored clothing is best.
Apply mosquito repellent to exposed skin. Spraying the outside of your clothing provides extra protection. Use a repellent that contains DEET or one that has oil of lemon eucalyptus, which comes from plants. Choose a strength based on the number of hours of protection you need. Products that contain more repellent aren’t stronger—they just last longer. Always use repellents as directed.
Don’t use DEET on infants under 2 months of age. Instead, you can use oil of lemon eucalyptus and cover your child’s stroller or playpen with mosquito netting.
Don’t apply any type of repellent to children’s hands. (Young children tend to put their hands in their mouths.)
Mosquitoes breed in standing water. To help reduce mosquitoes in your yard and neighborhood:
Remove anything that can collect water, such as old tires and empty cans, barrels, and flower pots.
Change water in birdbaths at least once a week. Clean a pet’s outdoor water bowl every day.
Drain unused swimming pools and remove collected water from pool covers.
Clean clogged gutters.
Install or repair door and window screens.
Report any dead birds to your local or state health department.
Fever over 101°F
Tremors (shaking muscles)
Paralysis (loss of movement)