People have debated fever’s purpose for centuries. Hippocrates imagined fever “cooking” illness out of the body, while by the 1700s many physicians treated fever itself as a dangerous disease. Today, fever is widely understood as part of the immune response shared by many animals, but exactly how a higher body temperature helps control infection remains unclear.
Sam Wilson, a microbiologist at the University of Cambridge, outlines two main possibilities: the heat of fever could directly damage or slow pathogens, or it could improve immune function, or fever might simply be a byproduct of immune activity. To test whether temperature alone can limit viruses, Wilson and colleagues designed an experiment that isolated temperature from other immune effects.
They used influenza as a model. Bird species have higher normal body temperatures than humans, and strains of influenza A that circulate in birds are adapted to replicate at those warmer temperatures. The researchers identified a genomic segment called PB1 that helps bird flu tolerate higher heat and inserted it into a human-adapted influenza virus. This produced two nearly identical viruses: a standard human strain and a heat-tolerant version.
Mice were chosen for the experiment because, unlike humans, they do not mount a fever in response to influenza, allowing investigators to manipulate ambient temperature without confounding fever-driven immune changes. Some mice were kept at standard lab temperature and others at a slightly elevated temperature that mimicked a fever. Animals were then exposed to either the normal human virus or the heat-tolerant hybrid.
At normal housing temperatures both groups of mice became ill regardless of the viral strain. At the elevated temperature, however, mice infected with the human-adapted virus were largely spared, while those infected with the heat-tolerant virus still fell ill. That finding supports the idea that higher temperatures by themselves can impede certain viruses.
Independent experts say the study strengthens the view that temperature is an important antiviral factor, though it does not rule out fever’s additional effects on the immune system—especially for viruses less sensitive to heat than influenza. Caution is also urged about directly extrapolating mouse housing experiments to human fevers.
The work adds to evidence that fever may have evolved as a useful response to infection and prompts practical questions about routine use of antipyretics like acetaminophen or ibuprofen. While treating very high fevers is often necessary to prevent tissue damage, whether lowering ordinary fevers routinely might slow viral clearance remains an open question.