West Nile is a moving target in more ways than one.

Not only is it carried by birds and mosquitoes, but the story of how it has emerged Canada continues to be in flight.

As the winter's snow blows, scientists are now assembling the picture of last summer's toll. The best numbers we can come up with is that there were 10 deaths officially linked to West Nile in Ontario with two other suspect cases. There was another death in Quebec. Upcoming studies will also document 1,000 cases of West Nile, where patients were sick enough to see their doctors and where blood tests were done.

But we may never know the exact toll, because of a myriad of problems that hindered doctors' ability to know how great the outbreak had become.

From early September when I became acquainted with some of the doctors on the front lines, where the bulk of the cases appeared, in Oakville, Mississauga and Toronto, there was a common message of frustration. It was taking them too long to confirm the cases. Blood samples had to go though three levels of tests -- including a test at the provincial lab and a confirmation from the federal lab in Winnipeg. That took weeks and, in many cases, months.

It might seem, on the surface, an acceptable problem: A system working hard to identify a new disease. But not so, say doctors who faced tough problems trying to decide how to treat patients for whom they had no diagnosis. This led to a larger problem. Without accurate data on how the disease was affecting humans, public health authorities couldn't make a decision on whether to spray against the mosquitoes carrying West Nile virus.

Take a look at the chart provided by Halton region, one of the areas with the largest number of human cases of West Nile. Surveillance data show that while dead birds were being picked up through July, there was a dramatic spike the first weeks of August. U.S. scientists had determined the threshold of risk to humans: 1.5 dead birds per square mile.

Halton Public Health put out an alert to doctors to be on the lookout for potential West Nile cases. And, in fact, within a week of this alert, there was a rise in the number of people complaining of fever, headaches, often accompanied by a rash. Doctors also began seeing a sudden rise in the number of people with viral meningitis (an inflammation of the membrane around the spinal cord and brain) and encephalitis, an inflammation of the brain itself.

The number of cases peaked three weeks after that rise in infected birds. It was a valuable piece of evidence for future West Nile virus control. (See Halton data)

But without a rapid diagnosis of cases, public health officials had no real idea of the scope of the problem, and it affected their ability to decide to spray.

Some doctors believe that may have led to more cases of West Nile, and more deaths from West Nile, than might have otherwise happened.

There are two issues with West Nile. One is what happened in 2002, and the other is how to best control the virus if it in fact emerges this summer, as most experts predict it will.

Several regions in the country, particularly in Ontario, are looking at mosquito control measures -- namely, larvacides, to kill the pests before they become adults.

Ontario has announced plans for faster testing, and a system of diagnosis confirmation that doesn't require samples to be sent to Winnipeg, to the federal laboratory.

The real measure of success will be if 2003 ends with few or no cases of West Nile in humans ... unlike what happened in 2002.