UK researchers: Watch for emerging, more infectious strains of avian flu virus



Poultry producers worldwide should be on the alert for emerging strains of avian influenza virus that are either more transmissible or cause more severe disease than prior strains.

According to researchers led by The Pirbright Institute in the UK, infection with two strains of avian flu also could lead to the emergence of a new virus strain with the potential to jump from birds to humans.

One study, published in the Journal of Virology, was conducted after a low-pathogenic H7N9 strain of avian influenza virus emerged in 2013 through genetic reassortment between an H9N2 strain and other low-pathogenic strains. The new H7N9 strain caused inapparent clinical disease in chickens, but zoonotic transmission caused severe and fatal disease in humans. Pirbright researchers looked at a natural reassortment scenario between H7N9 and a G1-lineage H9N2 virus predominant in India and across the Middle East.

Shared genetic information

According to Pirbright researchers, the study shows that avian influenza virus strains H9N2 and H7N9 can share genetic information to create an H9N9 strain with the potential to cause more severe disease in poultry and pose a threat to human health.

In collaboration with the UK Animal & Plant Health Agency, Pirbright researchers discovered that the H9N9 strain was able to multiply significantly better in poultry cells, indicating the potential to cause more severe disease. They also discovered that it had a higher replication rate in human cells and could bind to these cells better than H9N2. The H9N9 strain can infect and transmit between ferrets (a research model used for influenza), highlighting the potential to cause disease in humans.

Pandemic threat

The study shows that strains already circulating in poultry populations can exchange genetic material, leading to the creation of new strains, the Pirbright study said, which increases the risk of the virus jumping from avian hosts to humans and other mammals.

The investigators concluded that H7N9 and H9N2 viruses circulating in the same region can pose a pandemic threat, demonstrating the need for constant monitoring for the emergence of new virus strains.

“This is the first study to show that infection with circulating H9N2 and H7N9 influenza viruses could create new virus strains such as H9N9 that cause more disease in poultry and pose a greater risk to human health,” said professor Munir Iqbal, head of the Pirbright Avian Influenza Group.

He explained that if a host is infected with two different strains, there is always a chance that they will swap genetic material to create a new strain.

When this happens, it could lead to many outcomes. For example, the virus could become more or less able to cause disease in a host. It’s also possible a virus could acquire the ability to jump between hosts.

“This leads to viruses that primarily cause disease in animals having the ability to infect humans, which is what we have observed in this study,” he added. “More research is needed to determine which avian flu viruses could combine and pose a threat to poultry and human health.”


More infectious strains of avian flu virus

An illustration of the work carried out by Pirbright scientists. The image shows that when a chicken is infected with H7N9 and H9N2 strains of avian influenza, these viruses can reassort (swap genetic information) to create a strain that can bind better to cells, cause death in chicken embryos and spread disease in ferrets.

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