West Nile virus (WNv) and West Nile encephalitis

  • WNv is a mosquito-borne virus
  • “Encephalitis” means a swelling of the brain, and can be caused by many different viruses and bacteria. West Nile encephalitis is a type of encephalitis caused by WNv

Signs and Symptoms

  • Only 1 in 150 people infected will experience symptoms.  Only 20% of those infected will become seriously ill. Of these, 15% may be at risk for encephalitis.
  • Symptoms are flu-like and may include fever, headache, body aches, and/or a skin rash.
  • The elderly and people with weak immune systems are more likely to have severe cases.
  • The period from contacting the virus to having symptoms is usually 3-15 days.
  • See a doctor if you develop symptoms such as high fever, confusion, muscle weakness, severe headache, or stiff neck.


  • West Nile virus is spread to people and animals through the bite of infected mosquitoes.
  • The mosquitoes get the virus by feeding on infected birds.
  • The virus is NOT transmitted from person to person contact.


  • There is no specific treatment for this virus. Antibiotics are not effective. There are no vaccines approved for use against this virus.


  • Neurological effects may be permanent


  • When you are outdoors, use insect repellents containing DEET. Follow the directions. Do NOT use products with DEET on children under 2 years or pregnant women.
  • 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. 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 flowerpots, buckets and barrels. Change the water in pet dishes and replace the water in birdbaths weekly. Drill holes in tire swings so water drains out. Keep children’s wading pools empty and on their sides when they are not being used.

West Nile virus and encephalitis must be reported to the local Medical Officer of Health under the Health Protection and Promotion Act.