Flu transmission before the appearance of symptoms

The transmission of flu virus can occur before the onset of symptoms, making the control of epidemics a more difficult task. This is what is suggested by the results obtained by professor Wendy Barclay and colleagues, from the Imperial College of London, and published on PLoS ONE. The researchers put ferrets infected with the 2009 swine flu virus in contact with uninfected ferrets for short periods, at different stages after infection; what they found is that the virus was passed before the appearance of the first symptom – fever – both when the ferrets were in the same or in adjacent cages.
The main consequence of such a discovery is that “the spread of flu is very difficult to control, even with self-diagnosis and measures such as temperature screens at airports”, said prof. Barclay, since persons “might pass on an infection when they don't know they're infected”.
However, as usual in these cases, is better no to jump to hasty conclusions: “"Ferrets are the best model available for studying flu transmission,” said Dr. Kim Roberts, first author of the paper, “but we have to be cautious about interpreting the results in humans.”