Why colds are more common in the cold
It was dismissed by doctors for decades as a myth, but now scientists have proven that getting cold really can increase your chances of catching your death, or at least a rhinovirus!
Spread, quite literally, by coughs and sneezes, rhinoviruses are one of the most frequent causes of the "common cold". But while scientists had known that these viruses seem to grow better at cooler temperatures, they could never uncover the reason.
"There was no apparent difference in how the virus behaved when it was cultured at 33 degrees compared with 37 degree body temperature. It just grew much better, although we had no idea why," says Yale scientist Akiko Iwasaki, the author of a new study that has now proven why colds flourish better in the, er, cold.
"We thought, if it isn't the virus doing something different, perhaps it's our own cells working differently at the lower temperature..." Her insight proved to be right.
Iwasaki and her team found that the cells lining the airways are equipped with an inbuilt alarm system programmed to detect viral intruders by picking up the presence of viral genetic material inside cells.
"This sets off sensor molecules that cause the cell to sound the alarm by releasing signals called interferons that warn other cells nearby to turn on their anti-viral defences. This limits the spread of the infection," explains Iwasaki.
But it turns out that these sensors do not function properly at lower temperatures, like those encountered when cold air is inhaled through the nose in winter.
"When we tested cells from the airways in the culture dish we found that they produce fewer of these alarm signals and are less good at detecting an infecting virus at temperatures lower than body temperature," says Iwasaki.
The Yale team then went a step further and disabled the gene used by cells in the nose to make the sensor molecules. They genetically modified mice and infected them with the rodent equivalent of the common cold. In these animals, they found, the virus grew equally well at both higher and lower temperatures.
Regrettably, the study, published in PNAS this week, doesn't reveal a cure for the common cold yet, but it does highlight one reason why rhinovirus infections are more common in winter.
"The lower seasonal temperatures will keep our noses cooler, so the virus grows and spread better in the tissue," says Iwasaki.
The results also explain why rhinovirus infections remain restricted chiefly to the nasal passages rather than spreading to the lungs as other infections, like the 'flu, do...