#18,964
While I try to focus primarily on open-access studies that allow me to read them in their entirety, and hopefully lift an excerpt or two, every once in awhile I'll find a paywalled or copyright restricted paper that seems worthy of referral.
Today we've a study, published behind a paywall in Science, which shows that that avian-origin PB1 segments make human-adapted influenza A viruses more tolerant of febrile temperatures (~40–41 °C) in vitro and in a mouse model with artificially elevated body temperature.We've often talked about the fact that birds run `hotter’ than mammals, with a normal body temperature that hovers at or above 40°C, which would be considered a `fever level' in humans.
These viruses replicate primarily in the avian gut - which is several degrees warmer than the human airway - and it means that an avian virus must adapt to replicate at a lower temperature in order to become a bigger human threat.
One of the mutations we look for is (PB2-E627K); the swapping out of the amino acid Glutamic acid (E) at position 627 for Lysine (K) - which allows an influenza virus to replicate at the lower temperatures (roughly 33°C) normally found in the upper human respiratory tract (see Eurosurveillance: Genetic Analysis Of Novel H7N9 Virus).
Today's study looks at the impact of a different Avian-origin gene segment (PB1) and focuses on `two amino acid substitutions' (which, disappointingly are not specified in the abstract) that allow avian viruses to tolerate (and even thrive) at higher temperatures.
The human immune system's most obvious response to any infection is to mount a fever, which often slows or inhibits the replication of the invading pathogen. This is why many doctors suggest allowing a mild or moderate fever to run its course.
But an influenza virus that is both tolerant of higher temperatures and replicates at the lower temperatures in the human airway would complicate matters considerably.
As the authors point out, the pandemic viruses of 1918, 1957, and 1968 all acquired an avian-origin PB1, which may help explain why they were more virulent than seasonal flu.
While I'm more than a little hobbled by my lack of access to the full paper, the Editor’s summary and graphical and text abstracts are interesting enough for me to recommend that you might want to take a deeper look.
Avian-origin influenza A viruses tolerate elevated pyrexic temperatures in mammals
Matthew L. Turnbull , Yingxue Wang, Simon Clare, Gauthier Lieber , Stephanie L. Williams , Marko Noerenberg , Akira J. T. Alexander , Sara Clohisey Hendry , Douglas G. Stewart, [...] , and Sam J. Wilson +22 authors Authors Info & Affiliations
Science 27 Nov 2025
Vol 390, Issue 6776
DOI: 10.1126/science.adq4691
