Major Global Migratory Flyways – Credit FAO
If this year’s spread of highly pathogenic avian influenza (HPAI) seems somehow different from what we’ve seen in recent years, the chart below should confirm your suspicions. In just the first six months of 2015 we’ve seen twice the number of countries reporting HPAI than reported in all of either 2011, 2012, or 2013.
After the great bird flu diaspora of 2006-2007, where more than 50 new countries reported the H5N1 virus (see H5N8: A Case Of Deja Flu?), the number of countries reporting bird flu slowly began to decline. Although remaining endemic in places like Egypt, Indonesia, China, and Bangladesh, reports of H5N1 all but vanished from Europe and Africa after 2010.
The sharp increase in human H5N1 cases beginning in November of last year shows a similar spike, with the first half of 2015 already sporting more than double the greatest number of cases ever reported in a single year (mostly from Egypt).
Given the vagaries of Egypt’s reporting this total is probably somewhat conservative, and it doesn’t include the nearly 650 H7N9 human cases reported since early 2013 emanating from Eastern China.
To this we add the sporadic reports of human H5N6 infections in China (see Fatal H5N6 Case: Yunnan, China), the sudden global spread of HPAI H5N8 into Europe and North America over the past 8 months, and the steadily increasing number of reassortant offspring in the HPAI H5 lineage; H5N2, H5N3, H5N1 (North American), H5N5 & H5N9.
As if this litany of avian flu subtypes weren’t enough to worry about, each subtype contains numerous variants or clades within each subtype. Quite simply, the clade of H5N1 circulating in Cambodia is genetically different from the clade in Indonesia, or Egypt.
So when we discuss a flu virus – like H5N1, H7N9 or H5N8 – we aren’t talking about a single, monolithic threat. We are talking about an ever-expanding array of related viruses, which can vary considerably in their behavior and the threat they pose (see Differences In Virulence Between Closely Related H5N1 Strains).
Small wonder that last February the WHO issued a statement proclaiming H5 Currently The Most Obvious Avian Flu Threat, that cautioned:
Though the world is better prepared for the next pandemic than ever before, it remains highly vulnerable, especially to a pandemic that causes severe disease. Nothing about influenza is predictable, including where the next pandemic might emerge and which virus might be responsible. The world was fortunate that the 2009 pandemic was relatively mild, but such good fortune is no precedent.
An influenza pandemic is the most global of infectious disease events currently known. It is in every country’s best interests to prepare for this threat with equally global solidarity.
Typically, mid-summer is the absolute nadir of avian flu reports from the Northern Hemisphere. Yet this summer, we continue to see scattered reports of outbreaks in poultry (see CIDRAP News Diverse avian flu strains hit UK, Taiwan, South Africa), occasional human infections, and HPAI detections in wild and migratory birds.
Not enough to be alarming, but enough to notice.
While we can’t predict what comes this way this fall and winter (after all, H5N1 was on the ascendant in 2006 and then abruptly and unexpectedly stalled the following year), HPAI’s in general seem to be on an upward trajectory. And unlike H5N1’s last big surge in 2006, avian flu’s impact doesn’t hinge on the success or failure of single subtype.
If H5N1 strikes out, H7N9 is is on deck. If H5N6 goes into a slump, then H5N8 or H5N2 can pinch hit. Bird flu has a deep bench this year, and I don’t even want to think about what their draft choices next year might be.
OK, maybe a little bit too inside baseball. But you get the point. Whether temporary, or a new normal, the number of novel flu threats circulating out there are greater than we’ve ever seen before. And while that doesn’t guarantee a specific outcome, it does tend to stack the deck in the virus’s favor.
While the worst case scenario is that one of these HPAI viruses jumps to humans in a big way, it is not the only `bad’ outcome, nor is it necessarily the most likely.
Pandemics do happen, but they don’t happen all that often.
Other scenarios worth considering include:
- Asian H5N1 or H5N6 – both known to sporadically jump from poultry to humans – manage to follow H5N8’s example and turn up in North American wild/migratory birds and/or poultry.
- Asian H7N9 – which produces no symptoms in birds, making it incredibly difficult to detect and eradicate – hitches a ride on migratory birds and expands its range outside of China.
- The H5N8, H5N2, and H5N1 reassortments in North America begin to turn up in North American swine, posing a reassortment risk.
- One or more new HPAI subtypes emerge in China, North America, or around the world with uncertain impacts.
And of course, none of these have to happen for our existing HPAI H5 and H7 virus strains to wreak havoc on the world’s poultry industry, and by extension, inflict pain on the rest of the economy. In his testimony before a Senate hearing on avian flu last week, Dr. Tom Elam, president of FarmEcon LLC, estimated the economic losses to the US economy this spring from bird flu outbreaks conservatively at $3.3 billion.
Along with that go concerns for national security, particularly in areas of the world where food insecurity already runs high (see Food Insecurity, Economics, And The Control Of H7N9 & last May’s COCA Call: Diseases of Food Animals Threaten Global Food Security).
Understandably, the USDA and APHIS are both gearing up to deal with an uncertain fall and winter ahead (see APHIS/USDA Announce Updated Fall Surveillance Programs For Avian Flu). Other agencies – in the US and around the world – are preparing as well.
While no one can predict how this fall and winter will turn out on the avian flu front, the World Health Organization’s point made last February is worth repeating: