A Planet of Viruses - Carl Zimmer [4]
Kruse’s experiments made it clear that some tiny pathogen was responsible for the cold. At first, many experts believed it was some kind of bacteria, but Alphonse Dochez ruled that out in 1927. He filtered the mucus from people with colds, the same way Beijerinck had filtered tobacco plant sap thirty years before, and discovered that the bacteria-free fluid could make people sick. Only a virus could have slipped through Dochez’s filters.
It took another three decades before scientists figured out exactly which viruses had slipped through. Known as human rhinoviruses (rhino means nose), they are remarkably simple, with only ten genes apiece. (We have twenty thousand.) And yet that haiku of genetic information is enough to let the human rhinovirus invade our bodies, outwit our immune system, and give us colds.
The human rhinovirus spreads by making noses run. People with colds wipe their noses, get the virus on their hands, and then spread the virus onto door knobs and other surfaces they touch. The virus hitches onto the skin of other people who touch those surfaces and then slips into their body, usually though their nose. Rhinoviruses can invade the cells that line the interior of the nose, throat, or lungs. They trigger the cells to open up a trapdoor through which they slip. Over the next few hours, a rhinovirus will use its host cells to make copies of its genetic material and protein shells to hold them. The host cell then rips apart, and the new virus escapes.
Rhinoviruses infect relatively few cells, causing little real harm. So why can they cause such miserable experiences? We have only ourselves to blame. Infected cells release special signaling molecules, called cytokines, which attract nearby immune cells. Those immune cells then make us feel awful. They create inflammation that triggers a scratchy feeling in the throat and leads to the production of a lot of mucus around the site of the infection. In order to recover from a cold, we have to wait not only for the immune system to wipe out the virus but also to calm itself down.
The Egyptian author of the Ebers papyrus wrote that the cure for resh was to dab a mixture of honey, herbs, and incense around the nose. In seventeenth-century England, cures included a blend of gunpowder and eggs and of fried cow dung and suet. Leonard Hill, the physiologist who believed a change of temperature caused colds, recommended that children start their day with a cold shower. Today, doctors don’t have much more to offer people who get colds. There is no vaccine. There is no drug that has consistently shown signs of killing the virus. Some studies have suggested that taking zinc can slow the growth of human rhinoviruses, but later studies failed to replicate their results.
In fact, some treatments for the cold may be worse than the disease itself. Parents often give their children cough syrup for colds, despite the fact that studies show it doesn’t make people get better faster. But cough syrup also poses a wide variety of rare yet serious side effects, such as convulsions, rapid heart rate, and even death. In 2008, the Food and Drug Administration warned that children under the age of two—the people who get colds the most—should not take cough syrup.
Another popular treatment for the cold is antibiotics, despite the fact that they only work on bacteria and are useless again viruses. In some cases, doctors prescribe antibiotics because they’re not sure whether a patient has a cold or a bacterial infection. In other cases, they may be responding to pressure from worried parents to do something. But unnecessary prescriptions of antibiotics are a danger to us all, because they foster the evolution of increasingly drug-resistant bacteria in our bodies and in the environment. Failing to treat their patients, doctors are actually raising the risk of other diseases for everyone.
One reason the cold remains incurable may be that we’ve underestimated the rhinovirus. It exists in many forms, and scientists are only starting to get