25 June 2026
A new study demonstrates that a bovine H5N1 influenza virus replicates as efficiently in differentiated human nasal epithelial cells as the 2009 pandemic H1N1 strain.
While human spillover cases have occurred via close animal contact, sustained human-to-human transmission has not been observed. A critical bottleneck preventing avian influenza from spreading efficiently among humans is its typical inability to replicate robustly in the cooler environment (25-330C) of the human upper respiratory tract. To investigate this barrier, researchers utilized a advanced three-dimensional model of primary human nasal epithelial (HNE) cultures. They compared a bovine-derived isolate (H5N1 Tex/24) against the 2009 pandemic (H1N1 HH4/09) strain and older avian influenza variants.
The findings revealed surprising adaptions:
- At both 370C and 330C, the bovine H5N1 virus replicated just as efficiently as the pandemic H1N1 control, achieving peak titers of 10^8\TCID50\ml.
- Unlike classic mammalian adaptation markers such as the PB2-E627K mutation, the bovine virus utilizes alternative mutations PB2 M631L and PA K497R. Recombinant testing proved that these specific mutations are vital for driving efficient viral replication at the cooler 330C threshold.
- Infection with H5N1 caused a rapid and severe loss of respiratory cilia, dropping cellular coverage from over 82% down to 41% within 24 hours. This outpaced the damage caused by the pandemic H1N1 virus and threatens to severely compromise respiratory clearance mechanisms.
- The bovine virus actively suppressed early epithelial interferon (IFN-β and IFN-λ) responses at airway temperatures (330C), allowing it to multiply undetected during early infection stages. While the bovine virus can successfully block the production of new interferons in the upper airway cells, it cannot handle the body's wider, pre-existing immune defenses. Once the virus tries to spread further into the human respiratory tract or meets standard internal restriction factors (like MxA), the human immune defenses easily shut it down. It simply lacks the genetic toolkit required to resist human immune pressures well enough to jump easily from person to person.
Moreira, É. A., Constant, S., Constant, C., Butticaz, L., Wyler, M., David, T., Grin, P. M., Benarafa, C., Thiel, V., Alves, P. M., & Zimmer, G. (2026). A bovine H5N1 virus efficiently replicates in differentiated human nasal epithelial cells. npj Viruses.
