Bird flu viruses have been found to pose a particular risk to humans because they can replicate at higher temperatures, according to new research led by the University of Cambridge and the University of Glasgow. The study, published in Science, identifies a gene that plays an important role in determining how sensitive a virus is to temperature.
Researchers note that while human influenza A viruses typically thrive in the upper respiratory tract where temperatures are around 33°C, avian influenza viruses tend to replicate deeper in the lungs or even in the gut of their natural hosts, such as ducks and seagulls, where temperatures can reach 40-42°C.
The team used mice models to simulate fever conditions during influenza infection. Although mice do not naturally develop fever from influenza A viruses, researchers raised the ambient temperature to mimic fever’s effect on viral replication. They found that increasing body temperature was effective at stopping human-origin flu viruses from replicating but did not prevent avian flu viruses from spreading. Just a 2°C increase was enough to turn a lethal infection into mild disease for human-origin strains.
The study also highlighted the PB1 gene's role in making avian-like viruses resistant to high temperatures associated with fever. Viruses carrying this gene continued to cause severe illness despite elevated body temperatures. This is significant because when both bird and human flu viruses infect the same host—such as pigs—they can exchange genes.
Professor Sam Wilson from the Cambridge Institute of Therapeutic Immunology and Infectious Disease said: "Thankfully, humans don't tend to get infected by bird flu viruses very frequently, but we still see dozens of human cases a year. Bird flu fatality rates in humans have traditionally been worryingly high, such as in historic H5N1 infections that caused more than 40% mortality."
He added: "Understanding what makes bird flu viruses cause serious illness in humans is crucial for surveillance and pandemic preparedness efforts. This is especially important because of the pandemic threat posed by avian H5N1 viruses."
The findings may influence future treatment approaches for influenza infections. While fever is often managed with medications like ibuprofen or aspirin, there is clinical evidence suggesting that reducing fever may not always benefit patients and could potentially aid transmission of influenza A among humans.
Funding for this research came primarily from organizations including the Medical Research Council, Wellcome Trust, Biotechnology and Biological Sciences Research Council, European Research Council, European Union Horizon 2020 program, UK Department for Environment, Food & Rural Affairs, and US Department of Agriculture.
