History

• Where did West Nile virus come from?
• How did West Nile virus get to North America?
• Where has West Nile virus activity been reported in North America in the past?
• What is the history of West Nile virus in Canada?

Where did West Nile virus come from?

The virus was first isolated in 1937 in the West Nile district of Uganda. Since then, there have been outbreaks in Egypt, Israel, South Africa, and in parts of Europe, Asia and North America. The first recorded outbreak in North America happened in New York City in 1999.

How did West Nile virus get to North America?

No one knows for sure how the virus made its way to North America. There are many theories, including one that suggests the virus arrived on this continent through an infected migratory or imported bird, or through an infected mosquito that was transported to North America by accident.

During 2002, more than 4,000 people in North America became ill after being infected with West Nile virus. This is the largest outbreak of West Nile virus infection ever recorded.

Where has West Nile virus activity been reported in North America in the past?

For details about past human cases in the United States, including case counts and maps, visit the Centers for Disease Control and Prevention West Nile virus Web site.

For details about past human cases and activities in Canada, see PHAC's West Nile Virus Monitor under Maps & Stats.

What is the history of West Nile virus in Canada?

The first reports of West Nile virus activity in Canada came in August 2001, when the virus was found in dead birds and mosquito pools in southern Ontario.

Canada had its first confirmed human cases in 2002, after people tested positive for West Nile virus in parts of Quebec and Ontario. The virus was also found in birds, horses or mosquitoes in Nova Scotia, Quebec, Ontario, Manitoba and Saskatchewan. In addition, two people from Alberta became infected, but these cases are thought to be travel-related.

In 2003 over 1,400 clinical cases were reported from Nova Scotia, New Brunswick, Quebec, Ontario, Manitoba, Saskatchewan, Alberta, British Columbia and the Yukon. However in 2004, only 26 cases were reported in Quebec, Manitoba and Saskatchewan.

In 2005 more than 200 Canadians were diagnosed with West Nile virus. Almost half of these were in Ontario, with Manitoba and Saskatchewan equally sharing most of the remainder.

For situation reports and maps showing virus activity in Canada, visit Health Canada's West Nile Virus Monitor. This Web site also provides links to reports from provincial health ministries and regional / municipal health authorities.