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Influenza is transmitted even before there are obvious symptoms
Last reviewed: 01.07.2025
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Researchers at Imperial College London have studied the transmission of the flu virus in ferrets, suggesting that the disease may be transmitted before symptoms appear.
If the doctors' hypothesis is confirmed, it means that a person who is already infected will not be able to know about it. That is why it is so difficult to contain the waves of epidemics of this disease.
The scientists' work was carried out with the assistance of the National Institute for Health Research and the Imperial Biomedical Research Centre. The results of the research were published in the journal PLoS ONE.
For the experiments, scientists chose ferrets because these animals are susceptible to the same strains of flu as humans.
Healthy ferrets were exposed to influenza-infected ferrets by briefly placing them in a cage with infected ferrets.
As it turned out, the sick ferrets managed to "share" the virus with healthy ones even before the first symptoms of the disease appeared in the latter. Scientists also noted that it actually doesn't matter whether the animals are in the same or neighboring cages.
The findings are particularly important for planning how to combat influenza epidemics, said lead study author Wendy Barclay.
"Despite personal diagnosis of their condition, a person may not suspect that they are already sick. This is the greatest danger, because already infected people do not isolate themselves, but continue to contact healthy people," explains the author of the study.
During studies on ferrets, experts found that the first signs of the disease appeared 24 hours after infection, and the animals began to sneeze after 48 hours.
This confirms the results of earlier studies, which prove that a person does not necessarily have to sneeze to transmit the flu virus - germs are already released into the air during normal breathing.
In addition, experts concluded that at later stages, 5-6 days after infection, the infection is transmitted less frequently and does not “stick” as much. People can return to their normal daily activities.
"Ferrets are the best option for studying the transmission of influenza, but the results need to be interpreted with caution in relation to humans, as the symptoms and course of the disease depend on the specific strain of influenza," said Kim Roberts of Trinity College Dublin.