Infectious diseases know no borders, doctors remind
Helen Branswell, The Canadian Press
Published Friday, January 10, 2014 8:57AM EST
TORONTO -- A Toronto grandmother came home from Hong Kong with SARS. A Colorado woman visited a Ugandan cave and brought back to the United States an alarming souvenir -- Marburg fever, a cousin of Ebola. And now H5N1 bird flu has jumped the Pacific in the body of an Alberta woman.
If you ever wonder why public health officials worry about far-flung diseases -- the latest bird flu, the new MERS coronavirus -- the incidents above pretty much explain it.
Bugs travel. Or as public health folks like to put it, infectious diseases know no borders.
Sometimes they hitch rides in the lungs of unwitting and unwilling carriers, people like the unfortunate Alberta woman who contracted H5N1 flu in China during a visit to Beijing and died last week, or the Toronto woman who in 2003 stayed in the Metropole hotel at the same time as a doctor from China who was about to die from SARS.
Sometimes they travel in infected domestic animals. The movement of ducks and poultry in Asia certainly fuelled the spread of H5N1 throughout Southeast Asian poultry flocks in the mid-2000s.
They can even move in food: Canada's last foot-and-mouth disease outbreak, in 1952, is believed to have been started when an immigrant farm worker tossed the remains of a dried sausage he brought from Europe into a pig pen.
We humans move pathogens around, which means we don't have the luxury of dismissing an outbreak in some far off spot as "someone else's problem." It could too quickly be our problem too, experts say.
"We breathe the same air. We drink the same water. We fly on the same planes. And an infectious disease outbreak anywhere is a potential risk and threat to all of us," said Dr. Martin Cetron, director of the center for global immigration and quarantine at the U.S. Centers for Disease Control in Atlanta.
"And we just have to constantly pay attention and stay vigilant."
Some diseases do not spread well beyond the geographic regions where they are found. To date, Ebola and Marburg have largely plagued countries in parts of Africa. But the Colorado tourist and a Dutch woman who contracted Marburg after visiting the same Ugandan cave both travelled home after becoming infected. The American survived, but the Dutch woman died.
And then some diseases, like HIV, explode across the globe.
An outbreak of in 1981 is a perfect example of how travel can spread disease. That year, an outbreak of acute hemorrhagic conjunctivitis zipped around the globe along airline routes, says Dr. David Morens, a medical historian with the National Institutes of Allergy and Infectious Diseases, a part of the U.S. National Institutes of Health.
"It went from one airplane hub to another airplane hub and hopscotched all around the world and the outbreaks were right near where the airports were," Morens says.
Even before the dawn of air travel, the pattern of people taking diseases along with them on their travels was well established. In the 1300s, an outbreak of the plague -- the Black Death -- moved from likely the current Mongolia along trade routes to Turkey and into Europe, says Morens.
It is estimated the disease wiped out 60 per cent of the population of Europe at the time.
"These diseases that spread geographically from country to country spread by the prevailing means of travel of human beings of the time," he says.
"The pandemic of flu in 1957 was (moved about) mostly by boats. But 11 years later, in 1968 the next pandemic was mostly by airplanes."
"It's a recurring theme. In almost any era you go back to for the last few hundred years you'll find the same. The routes are different, the diseases are different, the mechanisms of conveyance of human beings are different, but the principle's the same."
The modern expansion of airline travel has increased the potential for disease spread. As more and more people travel more frequently, the territory that could accurately be described as "remote" is shrinking, Cetron suggests.
"We're much more closely connected than the distance on a map would argue," he says.
"There are very few places in the world where the dots cannot be connected within 72 hours. And that is getting pretty short. That is inside the incubation period of most diseases.... So the speed with which people move and the degree to which the globe is connected, even from remote, rural locations to the nearest urban airport to the next big hub is striking."
Interestingly people who follow H5N1 cannot recall another case where the virus moved this far from a source country. People from Hong Kong have been infected in China. But this is probably the first Transpacific voyage for this bird flu.
Still, Dr. Keiji Fukuda, the World Health Organization's assistant director-general for health security and environment, says watching for this type of movement is critical.
"From the public health perspective, what we're always looking for with these kinds of viruses is evidence that whenever somebody gets sick that maybe we're seeing the tip of the iceberg, that they're the first case that we're picking up and maybe the signal that we're going to see a lot of other people be sick because the virus has gained the ability to go from person-to-person," he says.
"We treat each new infection in the same way. We're always a little bit concerned: Is this the first sign of a change in these viruses' ability to infect a lot of people?"
Another reason is one Canada learned the hard way in 2003. Travelling pathogens can cause a lot of trouble once they land in a new locale.
The Toronto grandmother who stayed in Hong Kong's Metropole Hotel in February 2003 caught the bug that was about to kill the Chinese doctor; it claimed her life too after she brought it home. The chain of transmission she started resulted in about 438 probable and suspected cases of SARS in Canada, and 44 deaths.
If any country gets why far off disease outbreaks are a domestic threat, it's Canada, Fukuda says.
"What happened with Canada in terms of SARS being imported ... and then causing a major problem in Canada is one of the textbook lessons in modern public health," he says.
"So I think that Canada is really one of the countries that understands that even though something may have been happening over there in this world, over there means it may be on your doorstep really quickly."