One of the body's most fundamental defences against infection – a fever – may be powerless against bird flu, according to alarming new research from the University of Cambridge. This discovery could have profound implications for how we treat and prepare for potential outbreaks of avian influenza in humans.
The Body's Thermal Shield and Its Failure
The human body instinctively raises its internal temperature during an infection to create a hostile environment for invading viruses. This fever makes it significantly harder for pathogens to replicate, buying the immune system precious time to mount a defence and clear the disease.
However, the new study, published in the journal Science, suggests this thermal defence mechanism has a critical weakness. Typical human flu viruses reside in the upper respiratory tract, where temperatures are around 33 degrees Celsius (91F). A fever can push this to nearly 41C (106F), effectively slowing the virus. In stark contrast, bird flu viruses thrive in the lower respiratory tract and gut of birds, where ambient temperatures are a scorching 40 to 42C (104 to 108F) – a range that often exceeds what a human fever can achieve.
Laboratory Findings in Mice
To test how this temperature difference affects disease severity, scientists conducted experiments on mice. They used a modified, lab-grown PR8 flu virus, altered to be non-dangerous to humans, and tweaked its genetic code for viral replication to mimic either human or bird flu strains.
The mice were then infected and kept at ambient temperature or at a heat mimicking a human fever of 41C (106F). The results were striking. The human-like virus struggled to replicate under feverish conditions. The bird flu-like version, however, continued to copy itself relentlessly, causing serious disease despite the elevated temperature.
Dr Sam Wilson, a molecular virologist at Cambridge University who led the research, stated: '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.'
Implications for Treatment and Pandemic Risk
The findings challenge conventional medical wisdom. The evidence suggests that routinely treating a fever in a patient infected with bird flu may not always be beneficial, as the fever itself offers little defence.
Dr Matt Turnbull, a virologist at the University of Glasgow and the study's first author, emphasised the importance of vigilance: 'It's crucial that we monitor bird flu strains to help us prepare for potential outbreaks. Testing potential spillover viruses for how resistant they are likely to be to fever may help us identify more virulent strains.'
This research arrives amid growing global concern. A recent case in the United States saw a patient die from a novel strain of bird flu, marking only the second such fatality in the country. Since January 2022, the US has recorded 71 human infections, predominantly with the H5N1 strain, linked to outbreaks in poultry and dairy cows. French authorities have also warned that a bird flu pandemic could be deadlier than Covid-19.
While the immediate risk to the public is considered low, the study underscores the urgent need for continued research into how these viruses interact with the human body, as their inherent resistance to our primary thermal defence could make any future outbreak exceptionally severe.
