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Bird Flu Case in Canada: Where has H5N1 Been, Anyway?

Image: Officials test poultry in Hong Kong

Officials test poultry at the border with mainland China in Hong Kong as part of measures against the spread of the deadly H7N9 bird flu. A Canadian traveler has died from an unrelated strain of bird flu, the H5N1 strain. Philippe Lopez / AFP - Getty Images

Health officials are tracking the movements of a Canadian traveler who died last week after contracting an H5N1 avian influenza infection. They say it’s unlikely the traveler, identified in Canadian media as a woman in her 20s who had just returned from China, infected anyone else.

H5N1 bird flu dominated the headlines for years, only to be driven off the front pages first by a pandemic of H1N1 swine flu in 2009, and then by the new H7N9 avian influenza last year and the MERS coronavirus in the Middle East.

Health experts worry that any one of these three new viruses could change into a form that spreads easily from person to person. With modern air travel, any epidemic can become a global pandemic within days.

Here are some questions and answers about H5N1 bird flu:

So where has H5N1 been, anyway? The answer is: slowly cooking, causing the occasional infection but not flaring up like it did in the early years of its spread. Most of the recent cases have been in Cambodia. The latest H5N1 case was reported in Cambodia in November, making for 26 cases this year in that country. Most are in children, who get infected while caring for their family flocks.

Only two cases were reported in China last year, and just 45 cases since 2003, so public health experts will be asking how and where the traveler got infected.

"This is the first detected case of human infection with avian influenza A H5N1 virus in North or South America. It also is the first case of H5N1 infection ever imported by a traveler into a country where this virus is not present in poultry," the Centers for Disease Control and Prevention says.

How do officials know it’s not in North America? Because they are monitoring poultry and wild birds. There are dozens of types of avian influenza, and even strains like H5N1 have subtypes that kill a lot of birds and others that don’t. They’re called highly pathogenic if they kill birds, and in countries affected by H5N1, flocks of chickens often die off en masse and that tips off authorities that it’s circulating.

It doesn’t make most ducks sick, and experts believe the virus is spread by migrating waterfowl. U.S. Geological Survey and other officials have been testing wild waterfowl in Canada, Alaska, Maine and other places where migrating fowl are common and have not seen it yet. This is why it is highly unlikely that the unlucky Canadian patient caught H5N1 at home.

That makes H5N1 different from H7N9, by the way. For some reason H7N9 doesn’t make chickens sick when it infects them, which makes it more difficult to keep tabs on.

What happens to people who get it? Bird flu usually looks much like seasonal influenza, with coughing, fever and that sudden onset of weakness that makes patients feel like they’ve been hit by a ton of bricks. But it also tends to go right to the bottom of the lungs and cause pneumonia more quickly and easily than seasonal influenza. Patients often need breathing support and they often progress quickly to organ failure.

How do we know this Canadian traveler didn’t infect anyone else? H5N1 and H7N9 bird flu are still more adapted to birds than to people. They don’t have the genetic mutations that make them infect people easily. But you can be sure that officials will be checking everyone this traveler was in close contact with, as well as sequencing the genes of the virus infecting this particular patient to make sure it wasn’t a mutated version that can pass easily from person to person.

In addition, Canadian health officials say this particular patient had unusual symptoms. Instead of coughing, she had symptoms resembling a brain infection called encephalitis.

Why hasn’t H5N1 caused a pandemic yet? H5N1 first popped up in Hong Kong in 1997, and then reappeared in South Korea in 2003. It spread to 15 countries and caused immediate fears of a pandemic. But it’s never evolved into a form that easily infects people or spreads. That doesn’t mean it can’t – scientists have been playing with it in the lab, trying to make forms that would spread easily so they can study them to see if it’s possible for H5N1 to take on a form that both spreads easily and remains lethal as well.

Is there a vaccine against H5N1? Yes, companies have made one just in case, although flu vaccines are still made using fairly outdated technology and it would take weeks to scale up and make enough to vaccinate the world’s population. That happened with H1N1 swine flu in 2009. By the time enough vaccine was made to offer to hundreds of millions of people, the virus had already swept around the world. Drugs such as Tamiflu can help keep the disease from making people extremely ill if given quickly enough — within a day or two of infection.