West Nile Virus

If you develop signs of encephalitis, seek medical attention immediately.

Frequently Asked Questions

What is the West Nile Virus (WNV)?

Who is at risk for the WNV?

How is the WNV spread?

What are the symptoms of the WNV?

How long does it take to get sick if bitten by an infected mosquito?

What should I do if I think I have West Nile Virus?

What can I do to reduce my risk of becoming infect with WNV?

What is the West Nile Virus (WNV)?

West Nile is a mosquito-borne virus that poses a health risk.  Most infected people show only mild symptoms but for a rare few it can be a serious, possibly fatal disease.  It is not an airborne virus like the Flu or a cold.  It is transmitted through the blood.

Who is at risk for the WNV?

Everyone who is active and outside during the summer months such as gardening, golfing, walking or camping, should take precautions to avoid mosquito bites.  If you do work outside, avoid early morning and evenings when mosquitoes are most active.  Make sure you use all the protection measures to avoid contact with mosquitoes.

How is the WNV spread?

WNV is spread to humans by the bite of an infected mosquito, which became infected, by biting a bird that carries the virus. WNV is not transmitted person-to person, and is not spread by contact such as touching, kissing, or caring for someone who is infected.

What are the symptoms of the WNV?

Most people who are infected with WNV either have no symptoms or experience mild illness such as fever, headache and body aches before fully recovering. Some persons also may develop a mild rash or swollen lymph glands.     For a very rare few, the virus causes serious neurological illness such as neurological illness such as encephalitis (inflammation of the brain).  

If you have any of the following symptoms, seek medical help.   These may be early symptoms of West Nile virus illness, or of many other illnesses, so seek medical attention.

  • Rapid onset of severe headache
  • Muscle weakness
  • High fever
  • Stiff neck
  • Sudden sensitivity to light.
  • Confusion
  • Loss of consciousness (coma)

Extreme swelling or infection at the site of the mosquito bite is another reason to seek medical attention.  This may or may not indicate West Nile virus infection.

How long does it take to get sick if bitten by an infected mosquito?

Being bitten by an infected mosquito will not necessarily make you sick. Most people who are infected with West Nile virus have no symptoms or experience only mild illness. If illness were to occur, it would occur within 3 to 15 days of being bitten by an infected mosquito.

What should I do if I think I have West Nile Virus?

If you develop signs of encephalitis, seek medical attention immediately . These signs would include fever AND fluctuating levels of consciousness +/- rash +/- muscle weakness.

What can I do to reduce my risk of becoming infect with WNV?

Mosquitoes are attracted to darker, more intense colours so make sure you wear light colours when going outside between the hours of dusk and dawn and dress appropriately.  This should include:

  • Long sleeved shirts or jackets
  • Long pants and
  • Tuck pants into socks for extra protection
  • Consider using an insect repellent containing DEET (follow the directions on the package).   Ask your pharmacist for assistance when purchasing repellent with DEET.

*Never use anything labelled "insecticide" on your body*

Important Repellent Reminders

Use insect repellent:

  • Use only products that are federally-regulated such as those that contain DEET. The concentrations of DEET should be no greater than 30% for adults and no greater than 10% for children. Check the label for more detailed information or ask your pharmacist for assistance. Follow directions for use carefully.
  • Apply the repellent sparingly on the exposed skin surfaces or on top of clothing.   Do not use under clothing.   The repellent does not have to be applied heavily to be effective - a light coating will do.
  • Do not use repellent on open wounds, or if skin is irritated or sunburned
  • Do not get in the eyes - if this happens, rinse with water right away.
  • Wash skin with soap and water when you return indoors or when protection is no longer needed
  • Avoid breathing mist from spray-type repellent.   Always apply in a well ventilated area: never apply spray repellent inside a tent.
  • Do not use near food
  • Check for sensitivity - apply repellent to a small area of skin on the arm and wait for 24 hours before use
  • Do not apply repellent to children's hands or faces

For more information contact the Ontario Ministry of Health Information.