West Nile virus

The West Nile virus is a zoonotic disease (diseases spread from animals to people) caused by a flavivirus. West Nile virus is a found in Africa, West Asia, the Middle East and North America, including Canada. The virus is spread by the bites of infected mosquitoes and can cause illness in people, birds, horses and other animals.

West Nile virus is diagnosed by symptoms, history of exposure and laboratory testing. 

Most people do not have any symptoms. Mild flu-like symptoms can appear two to 14 days after exposure and include fever, headache, body aches, mild rash or swollen lymph glands. Certain people, especially the elderly, the young and those with weak immune systems are at greater risk for more serious illness. In these cases, symptoms could include severe headache, high fever, stiff neck, vomiting, drowsiness, confusion, muscle weakness and loss of consciousness. 

The West Nile virus is usually spread by the bite of an infected mosquito. A mosquito becomes infected with the virus after biting an infected bird. In a very small number of cases, the West Nile virus also has been spread through blood transfusions, organ transplants and during pregnancy. 

People who live in areas where West Nile virus is present are at risk.

Most people will recover without treatment. Supportive care and medications can be used to treat severe complications.

Health-care providers and laboratories must report cases of the West Nile virus to Public Health. Public Health staff may interview the health-care provider and patient (or caregivers) to find out how the infection occurred, identify other people at risk of infection, implement control measures and provide other advice. 

Ways to prevent mosquito bites in areas where West Nile virus is present include: 

• use insect repellents containing DEET or other Health Canada approved ingredients
• wear light-coloured protective clothing including long-sleeved tops, long pants and socks
• make sure door and window screens fit tightly and are free of holes
• minimize time spent outdoors at dawn or dusk, when mosquitoes are most active

Mosquito eggs develop into adult mosquitoes in small amounts of stagnant water. Take the following precautions to eliminate mosquito breeding sites:

• empty standing water and clean rain gutters regularly
• remove debris that can hold water, like old tires
• clean and chlorinate swimming pools and keep pool water circulating 
• landscape to eliminate standing water on property

For additional information, contact your health-care provider, local Public Health office or Tele-Care 811.