A UK study has shown that bird flu viruses continue to multiply in mice at high temperatures that would normally stop infection, explaining why some flu viruses are more dangerous to humans. 

Researchers at the University of Cambridge and the University of Glasgow mimicked fever by raising the ambient temperature in mice infected with a human-origin seasonal influenza A-like virus, or with a virus similar to avian flu.  

By increasing the animals’ body temperature by around 2°C, researchers recreated a fever response, which mice do not naturally get when infected with flu viruses. 

The higher temperature stopped human-origin flu viruses from replicating, protecting mice from severe infection. However, avian flu viruses continued to multiply and caused severe disease. The researchers identified that the PB1 gene, previously known to be important in the replication of the virus inside infected cells, was also responsible for the greater resistance to fever.  

When bird and human flu viruses infect the same animal at the same time, they often swap genes like the PB1 gene which could lead to the rise of more harmful flu variants affecting both humans and livestock. 

“Understanding what makes bird flu viruses cause serious illness in humans is crucial for surveillance and pandemic preparedness efforts,” said Sam Wilson from the University of Cambridge and lead author of the study published in Science.