The Uncommon Cold

Rhinovirus

Around 3,500 years ago, an Egyptian scholar sat down and wrote the oldest known medical text.
Among the diseases he described in the so-called Ebers Papyrus was something called resh. Even
with that strange sounding name, its symptoms—a cough and a flowing of mucus from the nose—are
immediately familiar to us all. Resh is the common cold.

Some viruses are new to humanity. Other viruses are obscure and exotic. But human rhinoviruses—
the chief cause of the common cold, as well as asthma attacks— are old, cosmopolitan companions.
It’s been estimated that every human being will spend a year of his or her life lying in bed, sick with
colds. The human rhinovirus is, in other words, one of the most successful viruses of all.

Hippocrates, the ancient Greek physician, believed that colds were caused by an imbalance of the
humors. Two thousand years later, the physiologist Leonard Hill argued in the 1920s that they were
caused by walking outside in the morning, from warm to cold air. The first clue to the true cause of
colds came when Walter Kruse, a German microbiologist, had a snuffly assistant blow his nose and
mix the mucus into a salt solution. Kruse and his assistant purified the fluid through a filter and then
put a few drops into the noses of twelve of their colleagues. Four of them came down with colds.
Later, Kruse did the same thing to thirty-six students. Fifteen of them got sick. Kruse compared their
outcomes to thirty-five people who didn’t get the drops. Only one of the drop-free individuals came
down with a cold.

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