"These findings offer useful insight into the potential of flu viruses to cause severe infection in humans" - 

PB1 gene helps infection to persist under high temperatures.

New research has shown that bird flu viruses can replicate at temperatures higher than a typical human fever, making them potentially more dangerous to people.

The study, led by the universities of Cambridge and Glasgow with involvement from the Roslin Institute, found that a gene of the virus, known as PB1, plays a crucial role in determining viral sensitivity to temperature.

Until now, researchers have not fully understood how fever prevents viruses, or why some viruses can survive high temperatures.

Professor Paul Digard of the Roslin Institute said: “These findings offer useful insight into the potential of flu viruses to cause severe infection in humans, and an understanding of the science underlying this threat.

“This aids our understanding of the relative risks of various flu types, and how we might best manage the fever response associated with viral infections.”

The study, published in Science, builds on evidence that some flu viruses can thrive in relatively high temperatures. For example, the lower respiratory tract and the guts of some birds can reach 40-42C.

Using mice, the team showed that fever protected flu viruses of human origin, with a two degrees celcius increase in body temperature. However, avian flu viruses resisted the fever and still caused severe illness.

Researchers also discovered that viruses carrying an avian-like PB1 gene could withstand fever temperatures, and caused severe disease. This is significant because human and bird flu viruses can swap genes when both viruses infect their host.

Dr Matt Turnbull University of Glasgow explained: “The ability of viruses to swap genes is a continued source of threat for emerging flu viruses. We’ve seen it happen before during previous pandemics, such as in 1957 and 1968, where a human virus swapped its PB1 gene with that from an avian strain. This may help explain why these pandemics caused serious illness in people.

“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.”

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