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Renewed Respect For Wild H5N1

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Part of the fallout from the publication of Yoshiro Kawaoka’s research paper (see Nature Publishes The Kawaoka H5N1 Study) has been renewed concerns over the progress the avian flu virus is making in the wild and its potential for sparking a pandemic.

 

A few headlines from the past 24 hours include:

 

Once-Banned Bird Flu Study Suggests Pandemic Threat Is Real Newsday.com

 

Bird flu viruses have potential to cause a ‘human pandemic' The Hindu

 

Study Shows How Bird Flu Could Jump to Humans - MedPage Today

 

Pandemic Potential? Bird Flu Becomes Airborne With Just 4 Mutations LiveScience.com

 

 

Kawaoka showed that it would take perhaps only 3 or 4 mutations to turn the H5N1 virus into a mammalian transmissible influenza, and noted that similar genetic changes have already been observed in virus samples collected from the middle east.

 

The `money quote’ from his paper was:

 

Therefore, these viruses may be several steps closer to those capable of efficient transmission in humans and are of concern.

 

 

Kawaoka references a 2011 study that found that several new H5 sublineages have emerged in Egypt with an increased affinity for (human) α2,6 SA receptor cells while still retaining their binding ability to (avian) α2,3 SA receptor cells.

 

We looked at this paper roughly a year ago in PLoS: Human-Type H5N1 Receptor Binding In Egypt.

 

Of note, in 2011 the authors found `increased attachment and infectivity in the human lower respiratory tract, but not in the larynx.’

 

Many scientists believe the virus must learn to bind to, and replicate in, the upper airway (nose, larynx, pharynx, trachea)  of humans in order to transmit efficiently from human to human. 

 

And that hasn’t happened in the wild yet.

 

Of concern, one of Kawaoka’s discoveries is a single mutation that `stabilizes’ the virus so that it can replicate within the pH range normally found in the trachea.

 

Some scientists worry that this pH stabilization might be one of the last big hurdles the virus must clear before becoming more of a human threat.

 

Whether the `right’ mutations will occur in nature, and at a time and place conducive for sparking a pandemic, is subject to debate. 

 

Some scientists argue that if it hasn’t happened by now, it isn’t likely to.

 

But it now appears that the number changes needed for the H5N1 virus to make a leap from being an avian-specific virus to a human-adapted one may be fewer than previously suspected.

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