A study authored by researchers at from Imperial College London and the University of North Carolina has revealed that avian influenza viruses do not thrive in humans because the temperature inside their noses is very low.
The researchers say that the new finding may help explain why bird flu viruses do not cause pandemics in humans easily.
In their study report, the scientists point out that there are 16 subtypes of avian influenza, some of which can mutate into forms that can infect humans by swapping proteins on their surface with proteins from human influenza viruses.
They say that normal avian influenza viruses do not spread extensively in cells at 32 degrees Celsius, the temperature inside the human nose, which is probably because the viruses usually infect the guts of birds, which are warmer, at 40 degrees Celsius.
Based on this observation, according to them, it may be said that avian flu viruses that have not mutated are less likely to infect people, as the first site of infection in humans is usually the nose.
When the researchers created a mutated human influenza virus by adding a protein from the surface of an avian influenza virus, they found it to struggle to thrive at 32 degrees Celsius. This indicates that any mutated virus would have to undergo further changes to adapt to the conditions in the human body.
The study also revealed that far fewer cells died as a result of infection with avian influenza compared with human influenza at 32 degrees Celsius, supporting the idea that the avian virus could not thrive at that temperature.
Professor Wendy Barclay, one of the authors of the study from the Division of Investigative Science at Imperial College London, said: "Bird viruses are out there all the time but they can only cause pandemics when they undergo certain changes. Our study gives vital clues about what kinds of changes would be needed in order for them to mutate and infect humans, potentially helping us to identify which viruses could lead to a pandemic."
Professor Barclay added: "It would be impossible to develop vaccines against all 16 subtypes of avian flu, so we need to prioritise.
By studying a range of different viruses in systems like this one we can look for warnings that they are already beginning to make the kinds of genetic changes in nature that mean they could be poised to jump into humans; animal viruses that spread well at low temperatures in these cultures could be more likely to cause the next pandemic than those which are restricted."
The study has been published in the journal PLoS Pathogens.