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



Canada's response to the potential swine flu pandemic of 2009 began, fittingly enough, with the late-night buzz of a BlackBerry.

Frank Plummer, scientific director of the National Microbiology Laboratory, was relaxing in his Winnipeg home, half-watching a hockey game, when an e-mail arrived from Celia Alpuche Aranda, head of the Mexican national microbiology lab. She was concerned about an ever-worsening outbreak of atypical pneumonia that scientists there were unable to identify.

Earlier that day - Friday, April 17 - the U.S. Centers for Disease Control and Prevention had alerted the World Health Organization to a seemingly unconnected occurrence: two unrelated children diagnosed with swine flu in California.

Dr. Aranda packed up samples from 51 seriously ill people in Mexico and shipped them to Winnipeg. She sent a similar package to the CDC in Atlanta.

Meanwhile, the flu hunters - the nickname given the epidemiologists and laboratory scientists who obsessively track the permutations of wily influenza viruses - were already at work.

While they usually toil invisibly, doing everything from mucking about farms in China wringing the necks of ducks to pulling all-nighters with genetic sequencers, their most powerful tool remains the gathering of information, pieced together like a puzzle.

Epidemiological information-gathering has become much easier with instant communication tools like e-mail. But cyberspace also poses the greatest challenge, because information - and fear - spreads a lot more quickly than a virus ever could, even one with pandemic potential.

Before Dr. Aranda's samples arrived in Winnipeg, the blogosphere was aflame.

On April 21, ProMed-mail, the blog of choice for flu hunters, posted a long item about swine influenza A H1N1, the virus identified in the California children, ominously noting the "possibility that human transmission of this new influenza virus has occurred."

Public health officials were also watching, with increased concern, an outbreak of flu in Mexico, a favourite vacation destination of Canadians. The Global Public Health Intelligence Network, an initiative of the Public Health Agency of Canada, sent out its first dispatch about an acute respiratory syndrome in Veracruz, Mexico, on April 10 and within days it was abuzz.

While there was no increase in flu activity in Canada, both the Ontario Agency for Health Protection and Promotion and the B.C. Centre for Disease Control sent alerts to public health units on April 21 telling them to watch for respiratory symptoms in Canadian travellers returning from Mexico.

Journalistic antennae went up too. Helen Branswell, the medical reporter at The Canadian Press, posted one of the first stories. "U.S. public health authorities are investigating two cases of swine flu in unrelated children in California, a development that has officials in Canada and elsewhere on alert," she wrote presciently.

On April 22, the CDC announced three more swine flu cases in the United States, and the Canadian Public Health Agency began investigating reports of Canadians returning from Mexico with a strange respiratory ailment. The initial fear was that SARS had returned.

But on the morning of April 23, Dr. Plummer, whose team had worked around the clock to analyze the samples it had received the day before, held a conference call with top Mexican health officials to reveal his findings: 17 of the 51 samples contained a completely new type of virus, one that had originated in pigs - swine influenza A H1N1.

In Canada, provincial health officials sent out a far more detailed alert, this time to physicians, about travellers returning from Mexico.

The arrival of a new flu virus, one that had eerie similarities to the killer Spanish flu of 90 years ago, told David Butler-Jones, Canada's Chief Public Health Officer, that it was time to activate the Canadian Pandemic Influenza Plan.

The World Health Organization also kicked it up a notch. A mere 22 minutes after receiving the results of the Canadian testing, the WHO opened its emergency operations centre. It also made the first explicit connection between the "influenza-like illness in the U.S. and Mexico" and convened a panel of international experts to determine the threat that swine influenza A H1N1 posed.

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.



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.

However, one should not be lulled into complacency by the fact that swine flu is not very contagious. The Spanish flu, the biggest killer of all time, had an R0 in the range of 1.2-3. Diseases that spread slowly and methodically like the flu tend to sicken and kill a lot more people than those that spread rapidly and burn out.

In an earlier Q & A, you wrote that "people who are infected with swine influenza A H1N1 will have immunity, or at least partial immunity, should there be a full-fledged pandemic." Pandemics tend to come in waves, the second worse than the first. So would it not make sense for healthy individuals to expose themselves to the flu to obtain some degree of immunity, trading a week of misery for protection against a possible more virulent second wave?

People raised in pre-immunization times will recall that mothers often staged chicken-pox parties so all the kids in the neighbourhood would contract the disease at once and get it over with. That was an effective (but slightly cruel) way of building lifelong immunity. However, holding a swine-flu party would be imprudent, for a number of reasons. The flu can be nasty; even a mild case can mean a week of fever, coughing and diarrhea. Second, there is no guarantee you will get a mild case of swine flu, even if you are infected by someone with a mild case. Influenza can be fatal and A H1N1 seems to hit kids particularly hard. Third, flu viruses mutate; if you deliberately get infected with a circulating strain of swine flu now, you may have only a little immunity later in a pandemic - so you get twice the misery. Finally, at and this is minor by comparison, is the aesthetics. At chicken-pox parties, kids got to play and the highly infectious virus did its work silently. At a swine-flu party, you would be dependent on a feverish, miserable host with the runs coughing on everyone - and you might also have to watch the slideshow from his Mexican vacation. If there is a vaccine for swine influenza A H1N1, will it be administered at the same time as the regular flu shot?

Preparations for the seasonal influenza vaccine that will be administered in the fall of 2009-10 are already well under way. It will take four to six months to develop a swine-flu vaccine, so it will not be added to the seasonal shot. If the swine flu becomes a serious threat, a vaccine could be produced urgently, but separately, and administered before the seasonal flu shots or at the same time. It is also possible that if the new flu virus continues to cause mostly mild disease, there will be no vaccination program.

Send your flu questions to



The flu in Mexico

Analysis of 1,280 cases shows children and young adults are most at risk of contracting H1N1 flu.


0-9 years: 24.1%

10-19 years: 23.7%

20-29 years: 19.4%

30-39 years: 13.6%

40-49 years: 10.1%

50-59 years: 6.7%

60+ years: 1.8%

Unknown: 0.6%


Mexico City: 11

State of Mexico: 2

Oaxaca: 1

Tlaxcala: 1



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