Influenza Virus Mashup

Influenza Virus Mashup

[Crof's H5N1] Dr. Vincent Racaniello: Ferreting out influenza H5N1

Posted by Automator On December - 7 - 2011

Much to my relief, Dr. Vincent Racaniello of virology blog provides some adult supervision after the last few days of "Omigod we're all gonna die" reporting: Ferreting out influenza H5N1. Excerpt (click through to read the whole post with its excellent links):

A laboratory in the Netherlands has identified a lethal influenza H5N1 virus strain that is transmitted among ferrets. These findings are under review by the National Science Advisory Board for Biosecurity (NSABB) to ensure that they do not constitute a threat to human health. 

Meanwhile both the popular and scientific press has been calling this a ‘virus that could change world history’. Even the usually restrained Helen Branswell writes that ”…the dangerous virus can mutate to become easily transmissible among ferrets — and perhaps humans…” Should we be frightened? 

Details of Ron Fouchier’s experiments are not known because the results have not yet been published. Reports at CIDRAP and Science indicate that Fouchier was attempting to make the H5N1 virus more transmissible in ferrets. This strain of influenza is lethal in birds and humans – there have been over 500 human cases with over 50% mortality. 

However, the virus is not readily transmitted among humans. The virus is lethal in ferrets but does not transmit among the animals. 

Fouchier selected a transmissible H5N1 variant by ferret-to-ferret passage. This experiment involves infecting a ferret, harvesting virus from the animal, and infecting another ferret. After ten such passages, the H5N1 variant could spread from one ferret to another by airborne transmission. The two amino acid changes that permit airborne spread among ferrets were identified. 

Scientists appear to be responsible for the hype surrounding this experiment. Fouchier called it ‘one of the most dangerous viruses you can make’. Paul Keim, chair of NSABB, ‘can’t think of another pathogenic organism that is as scary as this one’, and Richard Ebright, a molecular biologist at Rutgers University says the experiment should not have been done. Martin Enserink writing in ScienceInsider says that the virus could change world history, and similar proclamations of doom can be found in the popular press. 

I cannot fault the press for not having the background to interpret these studies, but scientists should know better than to declare that this is a dangerous virus. 

First and foremost, ferrets are not humans. Every influenza researcher will say that ferrets are a good model for influenza – they display similar flu-like symptoms, immune responses, and pathological alterations such as elevated temperature, weight loss, and histological changes. But it would be foolish to conclude that ferret influenza is the same as human influenza in all aspects. 

For example, not all influenza virus strains have the same virulence in humans and ferrets. A good example is the 2009 pandemic H1N1 virus which caused severe infections in some ferret studies, but was relatively mild in humans. 

In other words, just because the Fouchier H5N1 virus is transmissible among ferrets does not mean that it will be equally transmissible among humans. The experiment to answer this question cannot be done.

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