West Nile virus

Surveillance

Surveillance of West Nile virus detects the presence of the virus as early as possible in any area. This helps communities take steps to reduce risk. Surveillance activities vary by region. They depend on how often West Nile virus was seen in the region during previous years, and on Provincial and local surveillance policies.

The Centre for Food-borne, Environmental and Zoonotic Infectious Disease, a part of the Public Health Agency of Canada, produces a web page: Maps & Stats: West Nile Virus Monitor. Published weekly from May to October, the Monitor features reports and maps summarizing West Nile virus activity in Canada. Past reports are also available through links on this page.

Monitoring West Nile virus nationally is a joint effort between the Public Health Agency of Canada and numerous groups, including:

• Provincial and Territorial Ministries of Health
• the Canadian Wildlife Health Cooperative
• Health Canada's First Nations and Inuit Health Branch
• Canadian Blood Services
• Héma-Québec
• The Canadian Food Inspection Agency

Surveillance information is reported to the Public Health Agency of Canada by its partners and posted online every week. There may be occasional small differences between surveillance statistics on provincial and territorial websites and the Agency's website. These are likely due to delays in processing national information.

What is the role of bird surveillance?

When West Nile virus first came to North America, bird surveillance was used as an early indicator of the presence of the virus in animals. Experience from past outbreaks showed that crows, jays, magpies and ravens were highly susceptible to West Nile virus. Infected dead birds are a good indicator to determine whether people in particular areas are at risk. Some provinces and territories no longer conduct dead bird surveillance. Instead, they focus efforts on other surveillance activities.

The Canadian Wildlife Health Cooperative tests dead birds for West Nile virus. The Cooperative does this in collaboration with provincial laboratories and the Agency's National Microbiology Laboratory in Winnipeg. Testing occurs from late April until the first hard frost (usually in October).

For more information on dead bird surveillance in your region, visit the Canadian Wildlife Health Cooperative website.

What is the role of horse surveillance?

Among large animals, horses are especially at risk for West Nile virus infection and disease. For this reason, they too can act as an early warning system for West Nile virus activity in a region. The Canadian Food Inspection Agency monitors West Nile virus in horses with the help of:

• provincial veterinary laboratories
• veterinarians
• other members of the animal health community

What is the role of mosquito surveillance?

Mosquito surveillance depends on the level of anticipated or current West Nile virus activity in a particular area.

In areas where West Nile virus has not been found, surveillance of mosquitoes focuses on:

• which kinds of mosquitoes are present
• how abundant the mosquitoes are
• whether West Nile virus has entered the mosquito population

In areas where West Nile virus has already been found, mosquitoes may still be tested for West Nile virus. This information can help identify how different kinds of mosquitoes spread the virus to birds, animals and people. It can also be used to decide if, when, where and how to act to reduce the risk of infection by applying mosquito control measures.

Provinces and municipalities are responsible for control of mosquito populations.

What is the role of human surveillance?

Health care providers in Canada continue to be alert for symptoms of West Nile virus infection in their patients. They request laboratory tests when appropriate. They also report all probable and confirmed cases of West Nile virus infection to local and provincial health authorities.

Human surveillance information is used in a number of important ways. Knowing that West Nile virus is in an area puts doctors and the general public on special alert. It also provides more clues about who may be at highest risk for serious health effects from West Nile virus. In addition, human surveillance provides information to help ensure the safety of the blood supply in Canada.

What is the role of First Nations and Inuit community surveillance?

West Nile virus occurrence can change based on several risk factors including geography, weather and wildlife populations. Surveillance activities in First Nations and Inuit communities focus on birds and mosquitoes. The objective of these surveillance activities is to detect the presence of West Nile virus as early as possible in a given community. This ensures that decisions on the appropriate response activities can be made in a timely manner.

If West Nile virus is detected in a First Nations community, health officials are reminded that they must alert the Chief and Council. They will make sure that the community is aware and is taking steps to help prevent West Nile virus infections.

If anyone is concerned that they or a family member may have contracted West Nile virus, they should see a health professional.

Surveillance of West Nile virus provides information including detailed surveillance information about West Nile Virus in Canada since 2002.

For more information on West Nile virus epidemiology, transmission, prevention and control, refer to information for health professionals.