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West Nile Virus

West Nile virus is an illness that mainly affects birds. But infected mosquitoes can spread it to people and other animals after the mosquito bit a bird infected with West Nile virus. 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.

How Does West Nile Virus Spread?Bird, mosquito, and outline of person. Mosquito bites infected bird. Mosquito now carries virus. If infected mosquito bites human or another bird, virus may be passed on.

  • 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.

What Are the Symptoms of West Nile Virus?

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:

  • Fever

  • Headache

  • Muscle aches

  • Tiredness

  • Rash

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).

How Is West Nile Virus Diagnosed?

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.

How Is West Nile Virus Treated?

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.

How Can West Nile Virus Be Prevented?

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.)

  • Mosquito repellents can help protect you and your family from mosquitoes. Always follow the directions on the label. 

Mosquitoes breed in standing water. To help reduce mosquitoes in your yard and neighborhood:Man wearing long pants and long-sleeved shirt spraying mosquito repellent on clothes.

  • 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.

Call the Doctor

Contact your doctor if you have any of the following:

  • Severe headache

  • Stiff neck

  • Fever over 101°F (38.3°C)

  • Confusion

  • Tremors (shaking muscles)

  • Paralysis (loss of movement)


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