New Research Shows Bird Flu Can Withstand Fever — Raising Fears of Human Threat

By Staff, Agencies

New research from the universities of Cambridge and Glasgow warns that certain bird flu viruses may pose an elevated threat to humans because they can continue replicating even at the high temperatures generated during fever—one of the body’s primary antiviral responses.

The study, published in Science, identifies a key gene that helps determine how well a virus can tolerate heat, shedding light on why some avian influenza strains cause unusually severe disease in humans.

Influenza A viruses, which drive seasonal flu outbreaks, typically thrive in the cooler environment of the upper respiratory tract, around 33°C. By contrast, avian influenza viruses prefer regions of the body that are much warmer.

In their natural hosts—such as ducks and seabirds—the viruses often infect the gut, where temperatures reach 40–42°C. When these avian strains infect humans, they frequently target the lower respiratory tract, where temperatures are closer to 37°C.

Scientists have long known that fever, which can push human body temperature to 41°C, is an important defence mechanism that limits viral replication. But until now, the exact reasons why fever restrains some influenza viruses and not others have remained unclear.

Using mouse models, the research team simulated fever conditions and found that elevated body temperature effectively blocked replication of human-origin flu viruses. Even a two-degree increase was enough to turn what would normally be a lethal infection into a mild illness.

However, the same protective effect did not apply to avian influenza strains. Viruses that carried an avian-like version of the PB1 gene—a component essential for copying viral genetic material—remained stable and fully capable of causing severe disease despite fever-level temperatures.

This finding is particularly significant because human and avian flu viruses can exchange genes when they infect the same host, such as pigs, potentially creating hybrid strains with increased heat tolerance.

Professor Sam Wilson of the Cambridge Institute of Therapeutic Immunology and Infectious Disease said the results underscore the need for vigilant pandemic preparedness efforts. Although human infections from bird flu are rare, mortality rates have historically been high, as seen in H5N1 outbreaks that recorded fatality rates above 40%. Understanding which viral traits enable severe illness in humans, he said, is crucial for global surveillance.

The study also raises questions about the widespread use of fever-reducing medications such as ibuprofen and aspirin during flu infections. While the researchers caution that more work is needed, prior clinical evidence suggests that suppressing fever may sometimes worsen outcomes or even increase viral transmission.

The project received major funding from the UK Medical Research Council, along with support from the Wellcome Trust, BBSRC, the European Research Council, Horizon 2020, the UK Department for Environment, Food & Rural Affairs and the US Department of Agriculture.