West Nile virus and surveillance

Learn about West Nile virus (WNV) in Alberta, ongoing surveillance to identify cases and determine the risk each year.


West Nile virus (WNV) is transmitted to humans primarily through the bite of an infected mosquito. WNV can affect anyone – 1 in 5 people who are infected become ill. Severe neurological illness associated with the virus is rare, but risk increases with age.

The first evidence of WNV in Alberta was confirmed in July 2003.

Get more information about WNV on MyHealth Alberta.

The risk of WNV

There is a risk of WNV in Alberta every year. The majority of WNV activity occurs in southeastern Alberta (mainly grassland area). There have also been cases reported further north during seasons with more activity.

The period of greatest risk of WNV transmission to humans from mosquitos in Alberta usually occurs during the summer and depends on:

  • the number of Culex mosquitoes that have successfully survived the previous winter
  • the amount of WNV circulating in these same Culex mosquito populations
  • weather conditions in the spring and early summer affecting the spread of WNV between mosquitos and birds
  • how close human populations are to WNV-infected mosquito populations

WNV surveillance

WNV surveillance in Alberta

Each year, the Alberta government conducts passive surveillance for WNV in humans through the Alberta Precision Public Health Laboratory and Canadian Blood Services. Veterinarians and animal health laboratories report cases of WNV identified in horses.

Until 2009, surveillance of mosquito and bird populations was conducted in Alberta to determine when and where the greatest risk of WNV transmission to humans was occurring. This surveillance was discontinued when it was determined that risk of infection with WNV in Alberta was present every year.

The Interactive Health Data Application (IHDA) has more information on human cases reported in Alberta.

WNV in animals

WNV surveillance in Canada and United States

Government of Canada




British Columbia

Centers for Disease Control and Prevention, USA