West Nile virus

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 do become 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.

West Nile virus in Alberta

Each year, Alberta conducts passive surveillance for WNV in humans as conducted through public health laboratories and Canadian Blood Services. Veterinarians and animal health laboratories report cases of WNV identified in horses.

Between 2003 and 2008, surveillance of mosquito pools and bird populations was conducted in order to determine when and where the greatest risk of WNV transmission to humans was occurring. It has been determined that the period of greatest risk of WNV transmission to humans by mosquitos usually occurs between mid-July and mid-August, depending on the presence of consistent warm temperatures. The majority of WNV activity occurs in Southeastern Alberta (mainly grassland area), although there has been some activity reported further north.

An inter-organizational committee, the Alberta Arthropod-Borne Diseases Committee, meets regularly to review WNV and other mosquito and tick-borne disease risks that may affect the health of Albertans. In addition, Alberta Health will continue to participate in the national meetings that address WNV and other mosquito and tick-borne diseases in Canada.

The risk of WNV

There is a risk of WNV in Alberta every year. However, the risk varies depending on a number of factors:

  • 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 from mosquitos to birds and birds to mosquitos (amplification)
  • the proximity of human populations to WNV-infected mosquito populations

More information

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