Medical practice

New bird flu strain requires vigilance researchers warn

Most of the UK media are reporting on a worrying new strain of bird flu in China – the H7N9 strain of the bird flu virus.

According to the media, virology experts at a recent press conference warned that the virus "should not be taken lightly". This warning was prompted by new genetic research into the disease and by news that the virus is thought to have killed 24 people and infected at least 126 in China.

Public health authorities in the UK are reportedly on the alert to watch for any spread of the disease out of China. However, the H7N9 flu virus is currently thought only to be spread between birds and from birds to people.

It is possible that H7N9 could mutate (change) so that it can spread from person to person. This is why experts are investigating this disease, with a view to reducing the effects of a global flu pandemic (similar to the swine flu pandemic in 2009–10).

The new genetic research indicates that the virus might have evolved from at least four other flu viruses circulating in wild bird populations, ducks and domestic chickens. The study also found that H7N9 has already evolved into two separate strains since its emergence.

At the moment there is no need to panic and the risk to anyone living in the UK is only theoretical. But international health authorities will need to keep a careful watch on the spread of this new strain.

Where did the story come from?

The study was carried out by researchers from the Chinese Academy of Sciences in Beijing and the Chinese Centre for Disease Control and Prevention. It was funded by several public institutions in China, including the Ministry of Science and Technology.

The study was published in the peer-reviewed medical journal The Lancet.

The UK coverage of the study and press conference was accurate, with most news sources highlighting the need for vigilance rather than blind panic.

What kind of research was this?

This was a genetic analysis of the H7N9 bird flu virus, in which scientists used information taken from global virus databases to track the potential origins of the virus, as well as any genetic changes in the virus that have taken place since it emerged.

The authors point out that the H7N9 virus causing human infections was identified in China at the end of March 2013. As of April 18, the virus had spread to six provinces and cities, with 87 people infected and 17 fatalities. While this seems a worryingly high mortality rate, it is too early to say how this might change if the virus were to mutate to enable it to spread from person to person (rather than from bird to human as is currently the case).

Preliminary analyses have shown that the H7N9 virus causing the current outbreak in China may have originated from a number of existing flu viruses in wild birds, ducks and poultry. All bird flu influenza A viruses have a genome (genetic make-up) consisting of just eight single segments of RNA. But it is often the genetic simplicity of viruses that makes them so contagious.

One of these RNA segments codes for the protein haemagglutinin (HA), and another segment codes for another protein, neuraminidase (NA), both of which are crucial in helping the virus spread from cell to cell and from organism to organism.

HA and NA are present on the surface of the virus. HA plays a key role in the entry of the virus into a cell, and NA is involved in the release of the virus from the host cell.

The HA and NA proteins can be classified into different subtypes, which gives rise to the familiar HxNy classification of influenza viruses, where x stands for one of 17 possible subtypes of HA, and y stands for one of 10 NA subtypes.

What did the research involve?

Scientists used information taken from global virus databases to compare the H7N9 genome to other related flu viruses.

They carried out a detailed genetic analysis that enabled them to construct evolutionary (or phylogenetic) 'trees' – the viral equivalent of a family tree – for all eight RNA fragments of the virus. This allowed them to see what the current virus could have evolved from.

The researchers also tried to determine how the particular assortment of RNA particles present in the current H7N9 virus could have arisen, using genetic information. This was done to assess where the virus originated from geographically and the type of animal it had originally infected.

What were the basic results?

When two different types of bird flu virus infect the same cell at the same time, the new virus produced by the host cell can contain a mix of the RNA particles from each virus, generating new types of virus. This process is called reassortment.

The scientists concluded that the new H7N9 virus appears to have originated from at least four reassortment events.

The HA gene might have originated from a bird flu virus that normally infects ducks and the NA gene might have come from a virus that affects migratory birds, which may then have infected a duck. The other genes might have come from two different viruses that affect chickens. The reassortment of these genes could have occurred in ducks or chickens.

By comparing different samples of H7N9, the authors also noticed two genetically distinct strains of the virus, implying that it has already evolved further since it emerged.

How did the researchers interpret the results?

The researchers say the results suggest that the HA genes of the H7N9 virus were originally circulating in the East Asian fly way – a major route used by migratory birds spanning East Asia.

The NA genes seem to have been introduced by birds migrating from Europe, transferring to ducks in China via the East Asian fly way.

The six remaining RNA segments of the virus (referred to as internal genes) appear to have originated in two different groups of H9N2 viruses infecting chickens and ducks in eastern China. 

The researchers say that the most recent common ancestor of the H7N9 virus was probably in existence around January 2012, a time when migratory birds would have been wintering in areas of mainland China near to where the H7N9 outbreak has occurred. 

They stress the need for “extensive surveillance” of the virus in human beings, poultry and wild birds. Further evolution of the virus has the potential to make it more harmful to humans, either by making people more ill when they catch it, or by increasing its ability to transmit between humans, or both.

In a linked article in the Lancet, Dr Marc Van Ranst and Philippe Lemey of the University of Leuven, in Belgium, add that the history of the virus may be particularly important, because the low severity of the virus in birds probably allowed it to spread silently in domestic and wild birds. “Containing this hidden epidemic may prove very challenging given the magnitude of the domestic and wild bird populations in China,” they say.


This is important research tracking the origins of the new H7N9 bird flu virus, which gives some clues about how it might behave in the future. Scientists are particularly concerned that a future mutation could mean it is transmitted between humans, which increases the risk of a pandemic (an epidemic of infection across countries or continents).

For travellers to China and other countries affected by bird flu, it's important to observe the following precautions:

  • avoid visiting live animal markets and poultry farms
  • avoid contact with surfaces that are contaminated with animal faeces
  • don't eat or handle undercooked or raw poultry, egg or duck dishes
  • don't pick up or touch dead or dying birds
  • always follow good personal hygiene practices, including washing your hands regularly

Read more about reducing your risk of bird flu when travelling in affected countries.

NHS Attribution