Folklore holds that you “catch cold” from the weather, but in this modern scientific age we all know that the “common cold” is a virus, right? Nevertheless, it turns out humanity's most common infectious disease is more accurately named than we might think, struggling to reproduce in cells at our core body temperature, but flourishing a few degrees below. New research reveals there are multiple reasons why cold viruses prefer it cold.
Winter and the months on either side are the times when we are most prone to the blocked sinuses, sore throat, and sneezing referred to as a cold. Naturally, people, particularly in cold climates, have long blamed the weather. Mid-twentieth-century science pinned the blame for most colds on rhinoviruses instead, but left a lot of questions open about why these viruses are so seasonal.
As early as 1960 it was demonstrated that rhinoviruses replicate more efficiently at 33 to 35ºC (91 to 95ºF) than at our core body temperature of 37ºC (99ºF). Now Dr Ellen Foxman of Yale University has demonstrated that this abhorrence of high temperatures is not simply because the body is better at fighting back in the warmth.
Foxman has previously shown that part of the reason rhinoviruses don't do so well in cells at core body temperature is that cells produce more virus-fighting interferon proteins when it is warmer. However, in Proceedings of the National Academy of Sciences, she has shown this is not the whole story.
When Foxman introduced rhinoviruses to a culture of cells that don't produce interferons to fight the viruses she found that the invaders still died much more quickly at core body temperatures. “Through mathematical modeling, we discovered that the increased rate of cell death could account largely, but not completely, for the temperature-dependent replication of [rhinoviruses],” Foxman and her colleagues write.
The cold preference is the reason rhinoviruses predominantly infect the nasal passages, which tend to be at temperatures several degrees cooler than the rest of the body, particularly in cold environments. Although there is still some uncertainty about how the disease is transmitted, rubbing the nose and eyes with unwashed hands, which may have picked up the virus from others, appears to be a crucial step in the process. Once exposed to vulnerable cells at attractive temperatures, the viruses multiply to the point where they are ready to tackle the warmer environment of the lungs.
Whether the work will prove practical in helping stave off illness remains to be seen – you might be better off if you could find some way to keep your nasal passages permanently warm, but how to do that presents a tricky problem.