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July/August 2003 issue	IN THIS ISSUE: Table of Contents Feature: Boreal Firefighters The Inside Story Editor's Notebook Reverberations À la carte Mosaic Re:Sources

First isolated in humans in the West Nile region of Uganda 66 years ago, the virus spread, infrequently, through Egypt, Israel, South Africa and parts of Europe and Asia. North America's first human case appeared in New York City in 1999, and the virus has been moving across the continent, one bite at a time, every summer since. Canada's first human cases were reported in Quebec and Ontario in 2002, and by April 2003, there had been 325 confirmed cases and 18 deaths.

More than 150 North American species of birds, including crows, ravens, blue jays, robins, starlings and sparrows, can carry the disease. Mosquitoes become infected by feeding on the blood of infected birds. Within two weeks, they are capable of spreading the virus when they bite humans or animals, which they do by piercing the skin and injecting their tainted anticoagulating saliva as they draw blood through a syringe-like stylet. Infection in humans brings flulike symptoms: fever, headache and body aches, rash or swollen lymph glands. Those with weaker immune systems are at greater risk of developing more serious symptoms, including meningitis and encephalitis, both of which can be fatal.

One variable affecting the spread and severity of the disease is climate, according to Environment Canada scientist Adam Fenech. His hypothesis is that warmer-than-normal winters may compound the problem by allowing infected mosquitoes and migrating birds to overwinter and that summer heat waves encourage incubation and transmission. He is proposing that a new climate indicator, similar to the humidex, be developed for "WNV infection threshold days."

The patterns on the map (below) confirm that reports are increasing from east to west year by year. Some places may have fewer resources or less incentive to report accurately, but the overall picture of the spread of the virus is clear.

Crows are by far the most susceptible carriers of the West Nile virus. Reports of infected dead birds indicate that there are likely infected mosquitoes, such as Culex pipiens, in the area too. Scientists estimate that fewer than one percent of mosquitoes in any given area will become carriers of the virus.

Scientists estimate that fewer than one pecent of mosquitoes in any given area will become carriers of the virus. Two travel-related human cases in Alberta in 2002. Most cases have been located in southern protions of northern health districts.

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