How concerned should we be about H7N9 flu?

thinkstockphotos-87711730The past few weeks have seen an increasing amount of coverage about an ongoing outbreak of the H7N9 strain of avian influenza in China (often called ‘bird flu’).

Reports suggest that in January almost 200 people were confirmed as being infected with the virus, of whom 79 died. The WHO indicates that many of the people infected were likely to have been exposed to poultry or have been to environments where live birds are kept. This is in keeping with how the vast majority of human infections have occurred since the strain first emerged in 2013.

Does this year’s H7N9 outbreak represent something of wider concern? What are the chances that the virus will evolve and gain the ability to be transmitted between people, rather than from poultry to people? We asked Microbiology Society member Wendy Barclay, Professor of Influenza Virology at Imperial College London.

“I’ve got no inside knowledge other than what’s been reported, but I think that what we’re seeing is the annual trend in H7N9. Around this time of year, we nearly always see a burst of cases, likely because the climate in Southern China is perfect for flu transmission – it’s cold and dry, and quite good for the virus surviving in the environment.”

Earlier this week, evidence from China has shown that one of the surface proteins on the virus has mutated, allowing it to spread to any organ within a chicken, rather than just their intestines and respiratory tracts. This is clearly bad news for the birds, and the increased viral load might in turn result in an increased number of human cases. On the other hand – as was seen for H5N1, the other highly pathogenic bird flu – a virus that kills birds should be easier to spot and control than one that does not. But what is the current risk of H7N9 turning into even more of a public health risk?

“I don’t think that there is any reason to believe that the H7N9 that’s out there now is currently any more likely to cause a pandemic than the one that emerged in 2013,” Wendy explains. “We know that this virus can pass from chickens into humans, but we also know that it doesn’t appear to have the mutations required for person-to-person transmission.

“Genetic barriers still exist – H7N9 doesn’t have the mutations on its external proteins that would allow it to be transmitted through the air, or allow it to be stable enough to survive in the human respiratory tract.”

While the WHO say that at the current time there is “no evidence of sustained human-to-human transmission”, Wendy recommends that H7N9 requires close attention.

“Pandemic flu is rightly one of the top worldwide threats of most concern to researchers and public health officials, but while this current virus is the one that currently causes us the most worry, there are others out there in chickens, pigs and ducks that are also possible pandemic precursors. We continue to try to understand how better to predict which viruses will actually make it across the species barrier and how best to deal with them when they do.”

Benjamin Thompson

Professor Barclay is an Editorial Board Member of the Microbiology Society’s Journal of General Virology (JGV) and a winner of our Peter Wildy Prize. You can find out more about her work here.

You can read JGV’s collection of papers on avian viruses here.

Image credit: Hemera Technologies/Thinkstock
This entry was posted in Clinical and Medical Microbiology, Virology and tagged , . Bookmark the permalink.

2 Responses to How concerned should we be about H7N9 flu?

  1. Jennifer says:

    Do you think there is a possibility that the virus is mutating in chickens to allow it to infect more humans, so that it may, in a sense, study us and our immune defenses to find the right way to mutate that will allow it to spread from person to person and become a more serious threat the human race?

    Also, if bird flu ever did mutate in a way to spread person to person, how much of a catastrophe could this pose? I saw in a documentary that if this virus was able to mutate to spread person to person that the implications would be astronomical in a 3 month period of time.

    • Hi Jennifer,

      Good questions. We put them to Professor Barclay, and this is what she came back with:

      Do you think there is a possibility that the virus is mutating in chickens to allow it to infect more humans, so that it may, in a sense, study us and our immune defenses to find the right way to mutate that will allow it to spread from person to person and become a more serious threat the human race?

      It is difficult to imagine this working from an evolutionary perspective. As viruses replicate in chickens, the viruses that replicate the best in chickens will be selected. The virus can’t ‘see’ where it would go next, it has no purpose in mind. In the given environment that it experiences, the fittest virus will emerge. As the numbers of viruses in a chicken accumulate, there is a higher chance that one might be generated containing a mutation that enables increased replication in humans. However, this one would be a minority variant among all the other viruses in the chicken, making it less likely to actually be transmitted onward to a person, unless they were exposed to very high doses.
      ——

      Also, if bird flu ever did mutate in a way to spread person to person, how much of a catastrophe could this pose? I saw in a documentary that if this virus was able to mutate to spread person to person that the implications would be astronomical in a 3 month period of time.

      This is one of the important questions in the field: how much of the extreme pathogenicity will be retained after H5 or H7 flu viruses gain the mutations that allow for transmission between humans? There are at least two important changes that the virus must undergo to become transmissible, and both of those would be predicted to make it less severe in humans. However there is not a definitive experiment yet that confirms those predictions.

      We do know that severe influenza viruses can become transmissible (for example the 1918 influenza pandemic strain), but we still don’t entirely understand what drives the pathogenicity of that virus and how similar it is to the H5 or H7 strains that are in birds today.

      To sum up this answer: it is likely that the severity of a pandemic caused by a transmissible H5 or H7 virus would be greater than what we experienced in 2009 from the ‘swine’ flu. But how much worse is extremely difficult to quantify.
      ——

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