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The risks and benefits of influenza H5N1 research

29 January 2013 by Vincent Racaniello

Both Nature and the New York Times have weighed in on the resumption of influenza H5N1 research. In an editorial from 23 January 2013, Nature opines that “Experiments that make deadly pathogens more dangerous demand the utmost scrutiny”:

As several critics point out, the assessments of the relative risks and benefits of such research remain restricted to largely qualitative arguments. The formal, quantitative risk assessment common in the nuclear power and other industries could have helped to nail down and quantify risks, and would have informed the debate better. One year on, an irreproachable, independent risk–benefit analysis of such research, perhaps convened by a body such as the World Health Organization (WHO), is still lacking.

The Times editors, who looked foolish in January 2012 after remarking that the H5N1 ferret transmission research should not have been done*, simply tow Nature’s line.

To clarify a point, the Fouchier and Kawaoka experiments on influenza H5N1 transmission did not make the virus more dangerous – they made it less dangerous for ferrets. How they affect the virus in humans is unknown.

I suspect that no one, not even WHO, has done a quantitative risk-benefit analysis of H5N1 research because it cannot be done. What basic research will reveal is frequently unknown – if the outcome could be predicted, then it would not be research. Scientists ask questions, and design experiments to answer them, but the results remain elusive until the experiments are done. How can the benefits be quantified if the outcome isn’t certain?

For example, one of the benefits of influenza H5N1 research is to understand what regulates aerosol transmission of the virus. It is without doubt an important question, but whether or not research will provide an answer is unknown. At best, we might identify the determinants of aerosol transmission in ferrets – but not in humans. I don’t know the solution to this problem –  should we simply assume that we will get answers to all the questions we ask? Should we conclude that H5N1 research will allow us to understand H5N1 transmission and pathogenesis, thereby leading to vaccines and antiviral drugs or novel therapies? In this case there is no doubt that the benefits of H5N1 research are very high, but I can’t put a number on it. Nature calls this a ‘qualitative’ argument. But if someone tried to make a quantitative risk-benefit analysis of H5N1 research it would be fiction.

What is the risk of influenza H5N1 virus research? Many influenza researchers feel that it is low, if work with infectious virus is carried out under the right containment conditions. Perhaps the more relevant question is what is the risk of releasing experimental results that could be used for nefarious purposes. Because H5N1 transmission experiments utilize animal models, the results cannot be directly extrapolated to humans. If a virus is isolated that transmits by aerosol among ferrets, it cannot be concluded that the same virus will transmit among humans. Also remember that gain of aerosol transmission among ferrets was accompanied by a loss of fitness – the altered virus did not cause lethal disease when transmitted by aerosol. It seems unlikely that these research findings could be used to successfully produce a biological weapon.

It seems unlikely that someone intent on producing an H5N1 biological weapon would base it on work done in ferrets, or any other animal model. Their solution would be to passage the virus in humans – an unethical experiment, but which one could imagine being done by unethical individuals. Even the outcome of this experiment would not be assured – no one knows if an H5N1 virus selected for aerosol transmission among humans would have high lethality.

I understand why the Times would ask for a cost-benefit analysis of basic scientific research – the editors are not scientists and do not understand the unpredictable nature of research. But I expected more from the science journal Nature. Have the editors who wrote this opinion forgotten how scientific research is done?

*Without having read the papers, the Times editors decided that the H5N1 ferret experiments should not have been done. When the papers were published we all learned that the modified H5N1 viruses were not lethal to ferrets.

Filed Under: Basic virology, Commentary Tagged With: aerosol transmission, avian influenza H5N1, bioterrorism, ferret, fouchier, kawaoka, risk benefit analysis, viral, virology, virus

Kawaoka paper published on aerosol transmission of H5 influenza virus in ferrets

2 May 2012 by Vincent Racaniello

h5 ha changesOne of two papers on avian influenza H5N1 virus that caused such a furor in the past six months was published today in the journal Nature. I have read it, and I can assure you that the results do not enable the construction of a deadly biological weapon. Instead, they illuminate important requirements for the airborne transmission of influenza viruses among ferrets. Failure to publish this work would have compromised our understanding of influenza viral transmission.

The paper from Kawaoka’s group focuses on the viral hemagglutinin (HA) protein, an important determinant of whether influenza viruses can infect birds or mammals. In the image, the HA is shown as blue ‘spikes’ on the virion surface; a single HA molecule is shown at right. Avian influenza viruses prefer to attach to cells via a specific form of sialic acid that differs from the form bound by mammalian influenza viruses. This difference in receptor preference is one reason why avian influenza viruses do not transmit among mammals.

Kawaoka’s group used a random mutagenesis and selection approach to identify amino acid changes in the avian H5 HA protein that allow it to bind human receptors. These changes are located around the sialic acid binding pocket in the HA head (figure). Some of the amino acid changes were previously known, but there are also some new ones reported, expanding our understanding of how the HA binds sialic acids. Some of the HA amino acid changes allow virus binding to ciliated epithelial cells of the human respiratory tract (wild type H5 HA cannot). All of this is important new information.

The H5 HA genes with these amino acid changes were then substituted for the HA gene in a 2009 H1N1 pandemic virus, and this reassortant virus was inoculated intranasally into ferrets. The viruses did not replicate well in the ferret trachea, but viruses recovered from the animals contained a new change in the HA protein that improves replication. This change (asparagine to aspartic acid at amino acid 158) is known to prevent attachment of a sugar group to the HA and enhance binding to human receptors. Viruses with this change probably have a replicative advantage in ferrets.

A reassortant virus with HA amino acid changes N158D/N224K/Q226L transmitted through the air to 2 of 6 ferrets. Viruses recovered from one of the animals contained a new change in the HA protein, T318I. A virus with four amino acid changes in the H5 HA (N158D/N224K/Q226L/T318I) replicates well in ferrets and transmits efficiently, although the infection is not lethal.

Even more interesting are the results of experiments to understand how these HA amino acid changes affect viral transmission. The N224K/Q226L amino acid changes that shift the HA from avian to human receptor specificity reduce the stability of the HA protein. The N158D and T318I changes, which were selected in ferrets, restore stability of the HA.

There are three key questions concerning this work that must be answered.

Would an H5N1 virus with the changes N158D/N224K/Q226L/T318I transmit among humans? Probably not. The virus tested by the authors derived 7 of 8 RNA segments from a human H1N1 strain, which is well adapted for human transmission. It is likely that changes in other avian influenza viral proteins would be needed for human transmission. It might also be that entirely different changes in the H5 HA are required for transmission in humans compared with ferrets.

Is this information useful for the surveillance of circulating H5N1 strains; specifically, would the emergence of these HA changes signify a virus with pandemic potential? I don’t believe so. These are mutations that enhance the transmission of H5 viruses in ferrets, and their effect in humans is unknown. Ferret transmission experiments are not meant to be predictive of what might occur in humans.

If these results are not predictive of what might happen in humans, why were these experiments done? (to paraphrase Laurie Garret at the New York Academy of Sciences Meeting on Dual Use Research). A substantial portion of this work goes far beyond surveillance of H5N1 strains: it provides a mechanistic framework for understanding what regulates airborne transmission of avian H5 influenza viruses. In the Kawaoka study, amino acid changes that improve the stability of the HA protein were selected for during replication and transmission of the H5 viruses in ferrets. In other words, stability of the HA protein is an important property that allows efficient airborne transmission among ferrets. Additional experiments can now be designed to extend this idea. If such stabilizing changes can be shown to be important for transmission of human strains, then they might be a valuable marker of influenza transmission.

The Kawaoka paper is a significant piece of work that substantially advances our understanding of what viral properties control airborne transmission of influenza viruses. To view it as enabling construction of a bioweapon is highly speculative and fundamentally incorrect.

M. Imai, T. Watanabe, M. Hatta, S.C. Das, M. Ozawa, K. Shinya, G. Zhone, A. Hanson, H. Katsura, S. Watanabe, C. Li, E. Kawakami, S. Yamada, M. Kiso, Y. Suzuki, E.A. Maher, G. Neumann, Y. Kawaoka. 2012. Experimental adaptation of an influenza H5 HA confers respiratory droplet transmission to a reassortant H5 HA/H1N1 virus in ferrets.   doi: 10.1038/nature10831.

Filed Under: Basic virology, Information Tagged With: aerosol transmission, bioterrorism, dual use, ferret, H5N1, influenza, kawaoka, nsabb, viral, virology, virus

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