West Nile Virus

Aedes albopictus mosquito

West Nile virus (WNV) is most often spread by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. In North America, cases of WNV occur during mosquito season, which starts in the summer and continues through fall. WNV cases have been reported in all of the continental United States. There are no vaccines to prevent or medications to treat WNV in people. Fortunately, most people infected with WNV do not have symptoms. About 1 in 5 people who are infected develop a fever and other symptoms. About 1 out of 150 infected people develop a serious, sometimes fatal, illness. You can reduce your risk of WNV by using insect repellent and wearing long-sleeved shirts and long pants to prevent mosquito bites.

Quiz

Key Facts

  • WNV is the most common virus spread by mosquitoes in the continental United States.
  • There are no vaccines to prevent or medications to treat WNV in people.
  • Most people infected with WNV do not have symptoms.
  • About 1 in 5 people who are infected develop a fever and other symptoms.
  • About 1 out of 150 infected people develop a serious, sometimes fatal, illness.
  • You can reduce your risk of WNV by using insect repellent and wearing long-sleeved shirts and long pants to prevent mosquito bites

Media

Someone spraying insect repellent on another person's arm

Prevent Mosquito Bites

The best way to prevent infection with WNV is to prevent mosquito bites. Choose an insect repellent with one of the following active ingredients: DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol, or 2-undecanone.

Bird bath

Standing Water

Control mosquitoes inside and outside your home. Once a week, empty and scrub, turn over, cover, or throw out any items that hold water like tires, buckets, planters, toys, pools, birdbaths, flowerpot saucers, or trash containers. Mosquitoes lay eggs in or near water.

Mother applying repellent to son

Insect Repellent

Always follow instructions when applying insect repellent to children. Do not use insect repellent on babies younger than 2 months old. Do not use products containing oil of lemon eucalyptus (OLE) or para-menthane-diol (PMD) on children under 3 years old. Do not apply insect repellent onto a child’s hands, eyes, mouth, and cut or irritated skin. Adults: Spray insect repellent onto your hands and then apply to a child’s face.

Prevention Tips

  • Use Environmental Protection Agency (EPA)-registered insect repellents with one of the active ingredients: DEET, picaridin, IR3535, oil of lemon eucalyptus (OLE), para-menthane-diol (PMD), or 2-undecanone.
  • Cover up: wear long-sleeved shirts and long pants.
  • Keep mosquitoes out of your home. Use screens on windows and doors. Repair holes in screens to keep mosquitoes outside. Use air conditioning if available.
  • Once a week, empty and scrub, turn over, cover, or throw out any item that holds water, such as tires, buckets, planters, toys, pools, birdbaths, or trash containers. Check inside and outside your home.

For More Information

Page last reviewed: August 21, 2019