Fever helps the body fight off viruses: But how does it work?

"There are two main ideas, he says. The heat of a fever itself could be harming the virus, akin to Hippocrates' hypotheses. Alternatively, the heat is a means to an end, either stoking our immune system to work better, or simply a regrettable, but unavoidable byproduct of fighting off an infection. "The fact that there weren't definitive answers to these questions piqued my interest," says Wilson."

"Reaching this conclusion was tricky, says Wilson, since it's very difficult to disentangle the effects of a fever itself from the immune response that usually comes with it. "The stars had to align," he says. To put this question to the test, Wilson and his colleagues first needed a pathogen. They settled on bird flu, because birds run hotter than humans. The influenza A viruses that infect birds target their guts, which are a few degrees warmer than the airways favored by human influenza viruses."

Humans and many animals mount fevers as part of immune responses. Historical views ranged from Hippocrates' idea that fever 'cooks out' illness to 18th-century physicians who treated fever as harmful. Two main hypotheses exist: fever heat directly damages pathogens, or fever supports immune functions and is a byproduct of fighting infection. New mouse experiments indicate elevated temperature alone can impair some viruses, demonstrating a direct antiviral effect separate from immune activation. Those experiments used avian-adapted influenza A because its natural replication occurs at higher gut temperatures in birds than human airway viruses. Disentangling fever heat from immune activity remains challenging.

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