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Bird flu viruses are a particular threat to humans because they can replicate at temperatures higher than a typical fever, one of the body's ways of stopping viruses in their tracks, according to new research led by the universities of Cambridge and Glasgow.
In a study published today in Science, the team identified a gene that plays an important role in setting the temperature sensitivity of a virus. In the deadly pandemics of 1957 and 1968, this gene transferred into human flu viruses, and the resulting virus thrived.
How flu viruses thrive in the body
Human flu viruses cause millions of infections every year. The most common types of these viruses, which cause seasonal flu, are known as influenza A viruses. They tend to thrive in the upper respiratory tract, where the temperature is around 33°C, rather than deep in the lungs in the lower respiratory tract, where the temperature is around 37°C.
Unchecked, a virus will replicate and spread throughout the body, where it can cause illness, occasionally severe. One of the body's self-defense mechanisms is fever, which can cause our body temperature to reach as high as 41°C, though until now it has not been clear how fever stops viruses—and why some viruses can survive.
Unlike human flu viruses, avian influenza viruses tend to thrive in the lower respiratory tract. In fact, in their natural hosts, which include ducks and seagulls, the virus often infects the gut, where temperatures can be as high as 40°C–42°C.
Research methods and findings
In previous studies using cultured cells, scientists have shown that avian influenza viruses appear more resistant to temperatures typically seen in fever in humans. Today's study uses in vivo models—mice infected with influenza viruses—to help explain how fever protects us and why it may not be enough to protect us against avian influenza.
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