Avian Flu Diary: The Passing Pathogenic Parade

Flu Virus - Credit NIAID

# 7013

While the H7N9 virus outbreak in China has certainly captured everyone’s attention, public health officials caution that it is still too soon to know where this virus is headed.

Earlier today, Gregory Härtl - Head of Media for the World Health Organization – tweeted the following in response to questions regarding this virus.

It isn’t uncommon to see new (or re-emerging) infectious disease threats appear somewhere around world that raise serious public health concerns.

Most of the time, after an initial flurry of breathless news reports, the threat is found to be less than of pandemic proportion.

Of course, pandemics do happen.

Over the past 100 years, we’ve seen four influenza pandemics: The H1N1 pandemic of 1918, the H2N2 pandemic of 1957, H3N2 in 1968, and novel H1N1 in 2009.

Novel flu viruses are most likely to be zoonotic; jumping from another animal species to man, either directly, or through an intermediary host, or via reassortment.

Although pandemics are most often caused by influenza viruses, other diseases can qualify, as HIV has proven over the past 30 years.

While we’ve seen our share of pandemic contenders over the years, in truth, most fizzle out.

So today, a brief review of a few viral threats we’ve followed over past few years that sparked initial hyperbolic headlines, but have (thus far, anyway) failed to turn into a major public health threat:

In 2012 a novel Coronavirus appeared in the Arabia peninsula, and while it has sparked a couple of dozen infections (see ECDC: Epidemiological Update On NCoV) it continues to transmit inefficiently without sparking a major outbreak.
We’ve watched a number of triple-reassortant swine flu (Variant) viruses (H1N1v, H1N2v, H3N2v) make tentative jumps into human hosts (see An Increasingly Complex Flu Field), and so far they’ve failed to spread efficiently, or to produce substantial levels of morbidity.
In August of last year (see New Phlebovirus Discovered In Missouri) the CDC announced the detection of a novel tick-borne virus in America’s heartland. Despite being detected in 2009, only two cases have been reported.
In March of 2012, we learned of a new H17 flu subtype, carried by bats in an unusual host: bats (see A New Flu Comes Up To Bat).
In November of 2011 we saw a major die-off of seals in New England, that was eventually traced to a new mammalian adapted influenza virus mBio: A Mammalian Adapted H3N8 In Seals.
In October of 2008 doctors in Zambia and South Africa ran across a mysterious, previously unclassified virus that caused hemorrhagic symptoms in its victims similar to Ebola (see Lujo Virus: Newly Identified Arenavirus) While highly contagious, and fatal in 4 of the 5 identified victims, it has not reappeared since 2008.
The granddaddy of them all, H5N1 which emerged 15 years ago in Hong Kong, continues to affect birds in Asia, the Middle East, and parts of Europe and occasionally jumps to humans (WER: Update On Human Cases Of Influenza At Human-Animal Interface).

And to this list you can add Nipah, Hendra, H5N1, Ebola, Marburg . . . .

None of this is to suggest that these viruses are damp squibs, and that they pose no threat now, or in the future.

Over time, some (or all) could find opportunities to better adapt to human hosts, and their ability to cause epidemics or even a pandemic could change.

According to well respected anthropologist and researcher George Armelagos of Emory University, we are entering the Third Epidemiological Transition.

This third transition began in the late 1970s or early 1980s, and is hallmarked by newly emerging infectious diseases, re-emerging diseases carried over from the 2nd transition (which began with the industrial revolution, and added chronic, non-infectious, degenerative diseases), and a rise in antimicrobial resistant pathogens.

When you combine those factors with an increasingly mobile global population of about 7 billion people, and huge increases in the number of animals being raised for food consumption (often in environments conducive to the spread of diseases), and you have a recipe for explosive growth in diseases.

We live in an amazingly complex and interconnected world, where what happens at a poultry market farm in China, a pig farm in Belarus, or even at a cockfight in Indonesia can ultimately impact the health of millions of people around the world.

Whether the H7N9 virus has the `legs’ to spark a greater global health crisis is unknown right now. The next few weeks should tell us more.

But while we watch it, we must remember:

Another pandemic – regardless of its cause – is all but inevitable. We just don’t know when, and from where, it will come.

So vigilance, surveillance, and preparedness must be part of our ongoing response.

Influenza is regarded as the most likely pandemic threat, but you may wish to revisit the following blogs which look at a few non-influenza viruses with pandemic potential.