01/09/2014 09:04 EST | Updated 03/11/2014 05:59 EDT

Bird Flu May Have Come to Canada But it's No Reason to Panic

Yesterday's announcement that the H5N1 avian flu had led to a death in Canada has taken public health officials -- and the general public -- by surprise. This is the first time that this particular strain of the influenza virus has appeared in North America and could suggest that a pandemic is not far away. The fact that this happened during a potentially remarkable flu season has made this concern even greater.

But while the revelation, headed no less by the Minister of Health, Rona Ambrose, may signal the manifestation of many a fictionalized account of pandemics, the reality is that this is by no means a reason for panic. By taking a look at the influenzaviruses and how H5N1 has emerged, the reasons for calm become evident.

Influenzavirus is a species, not unlike poliovirus and norovirus. Within the species are a number of strains, denoted by a numbering system developed back in the 1970s. There are collectively over 100 strains, each divided into major categories -- A, B, C -- and specifically for the A viruses, a further division based on the chemical nature of two proteins, hemagglutinin (H) and neuraminidase (N).

There are 16 different types of H and 9 varieties of N. The majority of these strains are avian in nature although some have adapted to humans. The most common human strains are H1N1 and H3N2, both of which lead to the annual flu season. For the most part, these viruses are not killers and only a very small percentage of people die from infection.

Back in 1997, one strain, influenza A H5N1, which was thought to be solely avian in nature, began to appear in people in Hong Kong. The outbreak led to 18 cases and six deaths, which suggested a 33 per cent mortality rate, far higher than anything seen since the Spanish Flu of 1918.

Microbiologists around the world took notice of the situation and watched to see if this was a long awaited pandemic. In this pre-SARS world, everyone was expecting a 'Big One' to crop up and this virus had all the markings.

There was, however, a problem with that prediction. While H5N1 had infected people, they were not in turn infecting others. Unlike H1N1, this flu wasn't being spread in the population, the so-called human to human transmission. This is a pre-requisite for a pandemic. With some searching and analysis, researchers learned that the individuals who contracted the disease had maintained close contact -- close enough to kiss -- with live birds or other infected people. The likelihood of a pandemic went from probable to minimal and soon, after a massive kill-off of birds, nil.

For most, that was the end of H5N1 but a small number of people feared the virus would return. Eventually, it did rear its ugly hemagglutinin in 2003; this time in Thailand and Vietnam. Another two dozen infections were recorded with 18 deaths. The mortality rate was higher yet the virus still hadn't figured out how to spread effectively between humans. As with Hong Kong, the outbreak was stopped although there was less confidence that it would be gone for good.

As with many stories that appear to have a nearing climax only to realize that it will never come, researchers never saw the 'Big One' they expected. Though research has attempted to determine the path to a pandemic, there has yet to be any concrete evidence that the virus will ever be a more than an occasional blip on the public health radar. A pandemic is unlikely.

In the meantime, H5N1 has spent the last decade circulating primarily in a few countries, such as Indonesia, Egypt, Vietnam, and China. It has infected some 650 people and killed close to 60 per cent of them. It's dangerous but only if you happen to come into that kissing distance with an infected bird, other known infected animals such as pigs and tigera, or an H5N1 infected human. For almost all Canadians, these are not part of routine activities.

Over the coming days and weeks, more information will emerge and eventually public health officials will understand how this virus happened to infect the unfortunate woman and lead to her untimely death. More likely than not, the picture will be comparable to most other H5N1 infections that have happened in the past: isolated and unable to spread widely. While tragic, this case is certainly not the same as the one in seen in the movie Contagion.

As much as it may seem heartless, from a purely microbial health perspective, there may even be some good news here. H5N1 has now traveled outside of its usual borders and not started a pandemic; it continues to be a rogue virus incapable of starting anything more than an isolated case or small epidemic. For microbiologists and epidemiologists, there is much to learn; for media, plenty to deduce. For everyone else, this case reveals the fact that the potential for a pandemic exists and that we all need to stay aware of -- but not panic about -- our relationship with germs.


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