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Canada's 'flu hunters' track a wily new virus Add to ...

The pandemic alert level was already set at three on the six-rung ladder (representing none or very limited human-to-human transmission) because of the ever-present risk posed by avian influenza A H5N1, which continues to flare up sporadically around the world. That scale, which is a barometer of future risk of a pandemic (it does not reflect current severity), soon jumped to level four, then five.

Travellers carried the swine flu from Mexico to the far reaches of the world - by last Sunday, cases had been reported in 17 countries on five continents - but fear travelled far more quickly and widely.

While the news moved through cyberspace on a 24/7 news cycle, the public was able to follow the steady spread and rise in swine flu numbers. The genome of the influenza A H1N1 virus was decoded in record time, revealing that it consists of a strange hybrid of North American swine influenza, North American avian influenza, human influenza and swine influenza typically found in Asia and Europe.

One of the first things scientists at the CDC in Atlanta and the NML in Winnipeg did was start growing seed stock from the virus, the fundamental element needed for a vaccine. Production of the vaccine could begin in mid-May; a final product could be on the market within four months, and about two billion doses produced within a year.

While not many of the swine-flu hunters are getting their hands dirty on hog farms, there is no shortage of grunt work.

A group of North American scientists - including four lab workers from the National Microbiology Laboratory - essentially built a new lab from scratch in Mexico City so they no longer have to send samples to Canada and the United States for testing. It was up and running on April 26. That has greatly speeded up testing, but has also given the impression that the virus continues to spread quickly in Mexico, which is not necessarily the case.

The laboratory work is also providing important clues on the epidemiology of the disease. It revealed that the first case of influenza A H1N1 occurred in Mexico on March 17, and the first case in the United States on March 28. The first death from swine flu was a 39-year-old woman who died on April 12 in Oaxaca, a popular tourist area. On that same day, a farm worker who had just returned from holidays in Mexico is believed to have infected pigs on a farm in Alberta.

This data is a comfort to flu hunters because it reveals that the virus has actually been circulating for about six weeks, meaning that many more people in Mexico (as well as travellers to the country) have been exposed to the virus than previously believed, without falling ill.

In coming days, information will be published on the fatality rate and severity of the flu to date, which will provide hard data for modelers and risk assessors to better determine where the pandemic may or may not be going.

Still, in our impatient world, there is not always a willingness to give the flu hunters the time to do their painstaking work. Nor is there, in the BlackBerry age, a recognition that influenza, an ancient disease, moves at its own pace, more often than not slowly and relentlessly.

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Q AND A: IT'S NO PARTY

How contagious is the swine flu and how does it compare to other diseases?

To measure how contagious an infectious disease is, scientists use a measure called the "basic reproductive rate" (R0 or R-zero for short) - the average number of people a disease carrier infects. To date, swine influenza A H1N1 appears to have an R0 of 1.5-2, which is quite low. By comparison, seasonal influenza has an R0 of 1.5-3, SARS was 2-5, polio 5-7 and measles 12-18.

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