Scientists Discover Resurgence of Avian Influenza Virus Strain

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Nature Exclusive: Scientists Discover Resurgence of Avian Influenza Virus Strain – Evolution Proves Extremely Lethal

Nature Exclusive: Scientists Discover Resurgence of Avian Influenza Virus Strain – Evolution Proves Extremely Lethal

Genetic mutations in avian influenza virus have led to its spread in many wild species, causing uncontrollable global outbreaks.

Researchers conducted a study on the evolution of avian influenza virus over the past 18 years.

The results indicate that the currently prevalent strain globally is an extremely deadly H5N1 subtype, which is becoming increasingly infectious in wild birds.

This virus strain emerged in Europe in 2020 and has since spread to an unprecedented number of countries and regions.

This research was published in the October 18th issue of “Nature” under the title: “The episodic resurgence of highly pathogenic avian influenza H5 virus.” The researchers observed changes in the virus’s genome over time and tracked its spread using reported epidemic data.

Nature Exclusive: Scientists Discover Resurgence of Avian Influenza Virus Strain - Evolution Proves Extremely Lethal

The study found that in 2020, the rate of transmission of the influenza virus among wild birds was three times that of poultry, due to mutations that allowed the virus to adapt to different species.

Andy Ramey, a wildlife geneticist at the US Geological Survey’s Alaska Science Center, stated, “What was once a clearly poultry pathogen has now become a broader animal health concern. This affects both wild animals and poultry, as well as the humans who depend on these resources.”

Avian Influenza Continues to Erupt

H5N1 virus is classified as highly pathogenic avian influenza (HPAI) because it causes significant poultry mortality and was first discovered in birds in China in 1996.

Outbreaks typically occur seasonally, synchronizing with the migration of birds in the northern hemisphere during autumn.

However, since November 2021, outbreaks have been ongoing. In 2022, the virus led to the deaths of millions of birds across five continents and triggered outbreaks in mink farms and various marine mammals.

Nature Exclusive: Scientists Discover Resurgence of Avian Influenza Virus Strain - Evolution Proves Extremely Lethal

To study changes in the virus’s behavior, the authors analyzed data reported to the United Nations Food and Agriculture Organization and the World Animal Health Organization from 2005 to 2022, and examined more than 10,000 virus genomes.

Their research revealed that in the mid-2020s, a new strain of H5N1 virus evolved from the earlier H5N8 strain, which first appeared in poultry in Egypt in 2016-2017 and caused global outbreaks of avian influenza in 2020 and 2021. The new H5N1 virus variant emerged through interactions with a non-lethal avian influenza virus that had been prevalent in European wild birds since 2019.

In 2021 and 2022, it developed into two subtypes, with one spreading in northern central Europe and eventually carried to North America by migratory birds, while the other subtype spread around the Mediterranean and entered Africa.

The study found that many avian influenza outbreaks originated in poultry but spread to wild birds, causing the disease to spread to larger regions, posing a difficult-to-manage global challenge.
One of the study’s co-authors, Vijaykrishna Dhanasekaran, an evolutionary biologist and virologist at the University of Hong Kong, said, “Once the virus adapts to wild birds, we have no mechanism to control the virus. I think this is the most significant change happening now.”

Louis Moncla, an evolutionary virologist at the University of Pennsylvania in Philadelphia, agreed with this view. “No matter how many epidemic control measures you implement in poultry, if it keeps entering from wild birds repeatedly, it’s really hard to manage. At this point, most countries around the world share responsibility.”

Viral Genetic Reassortment

Low-pathogenic avian influenza viruses frequently circulate freely among poultry and wild birds. It is believed that previous exposure to these non-lethal strains promotes herd immunity in wild birds. Ramey explained, “You can think of it as an imperfect vaccine. It doesn’t prevent infection but helps mitigate the impact of the disease.”

However, he added, “This may be a double-edged sword.” Highly pathogenic avian influenza viruses can evolve through interactions with low-pathogenic avian influenza viruses. Both types of viruses have their genomes divided into eight segments that can mix and match. When both viruses infect the same cell, they can exchange genes during viral packaging.

As a result, low-pathogenic avian influenza viruses, especially a strain called H9N2, play a crucial role in the evolution of H5N1 virus. However, these viruses have not been well-monitored. Strategies to eradicate or eliminate these low-pathogenic viruses will be a significant step in controlling avian influenza itself.

Nature Exclusive: Scientists Discover Resurgence of Avian Influenza Virus Strain - Evolution Proves Extremely Lethal

Unsustainable Culling of Birds

The ongoing H5N1 highly pathogenic avian influenza outbreaks repeatedly spill over from poultry, increasing the risk of zoonotic diseases and pandemics. Culling is a common method to contain the spread of highly pathogenic avian influenza in poultry and has led to the culling of millions of poultry.

However, due to the increasing resilience of H5 highly pathogenic avian influenza in wild birds, continuous culling is unsustainable. The large-scale deaths of wildlife have raised concerns about biodiversity loss and disruption of ecosystem balance. Therefore, Europe and North America are increasingly considering the use of subsidies for poultry vaccination to prevent outbreaks.

Some countries in Asia and Africa use vaccination, but the effectiveness varies. In some regions of Hong Kong, mainland China, and Southeast Asia, vaccination is combined with other control methods. The diverse and incomplete vaccination strategies in regions near northern Africa, the Middle East, and Eastern Europe are also a cause for concern.

In summary, addressing these issues requires strengthening global surveillance and improving comprehensive strategies for epidemic prevention and control.

A better understanding of the ecological characteristics that promote and sustain the spread of wild birds and the consequences of varying poultry vaccination rates is crucial in mitigating future highly pathogenic avian influenza outbreaks.