A Silent Viral Threat Emerging
While most global attention remains fixed on the deadly H5N1 bird flu, scientists now warn that another strain — H9N2 — could pose an even subtler but serious threat.
Researchers from the University of Hong Kong report that H9N2, long seen as a “minor” avian influenza virus, has evolved genetic traits that make it better suited to infect humans. The findings were presented at the Pandemic Research Alliance Symposium in Melbourne, Australia.
“H9N2 is receiving less attention than it deserves,” said Dr. Kelvin To, microbiologist at the University of Hong Kong. “It’s already the second most common bird flu strain infecting humans.”
From Birds to Humans: A Hidden Transition
Since 1998, 173 human infections with H9N2 have been officially reported — mostly in China. But many experts believe the real number is higher because mild infections often go undetected.
According to Michelle Wille of the Peter Doherty Institute, people infected with mild H9N2 cases often aren’t hospitalized or tested, allowing the virus to circulate quietly.
“H9N2 may be one of the non-human influenza viruses most likely to cross the species barrier,” said Prof. Gian Carlo Icardi of the University of Genoa.
Genetic Changes Point to Human Adaptation
Although human-to-human transmission has not been confirmed, scientists are increasingly concerned about the virus’s evolution.
Studies show that since 2015, H9N2 has developed mutations that make it more capable of infecting human respiratory cells. In laboratory tests, a 2024 sample infected far more human cells than an older 1999 version.
These mutations involve the virus’s hemagglutinin (HA) and neuraminidase (NA) proteins — the same components that define all influenza strains. The new structure allows H9N2 to bind more easily to receptors found in the human respiratory tract, suggesting early adaptation to people.
“H9N2 has developed features that make it increasingly compatible with human cells,” explained Icardi. “That’s a sign we can’t ignore.”
Surveillance Gaps Leave the World Exposed
Unlike highly pathogenic strains like H5N1, countries are not required to report H9N2 infections because it’s considered a “low-pathogenic” virus. This lack of mandatory reporting allows it to spread silently among wild birds, poultry, and mammals that live in close contact with humans.
Experts warn that this oversight could delay the detection of a dangerous mutation.
“Enhanced monitoring among mammals exposed to wild or domestic birds could reveal whether the virus is adapting to new hosts,” Wille said.
The Risk of Viral Reassortment
Another major concern is viral reassortment — when two influenza viruses infect the same host and exchange genetic material, potentially creating a new hybrid virus capable of efficient human transmission.
Genetic traces of H9N2 have already been found in other avian flu strains that infected humans in past outbreaks.
“Influenza viruses are master shape-shifters,” said Icardi. “Understanding their evolution helps us prepare before they adapt fully to humans.”
Why Global Surveillance Matters
For now, the H9N2 strain does not appear capable of causing sustained human outbreaks. But experts say its evolution is a warning sign that pandemic preparedness must remain a global priority.
“H9N2 may seem minor today, but it’s evolving in ways that demand vigilance,” said Dr. To. “Preparedness means tracking these changes — not waiting for the first major outbreak.”
Scientists urge stronger avian influenza monitoring programs, cross-border data sharing, and collaboration between animal and human health agencies to catch early warning signs.
🧭 Key Takeaways
- H9N2 is evolving to infect humans more efficiently.
- Researchers from the University of Hong Kong warn of growing pandemic potential.
- Genetic mutations since 2015 show human cell adaptation.
- Lack of surveillance could allow silent spread.
- Stronger global influenza monitoring is needed to prevent another pandemic.
Original text: repubblica.it
About The Author
