The diversity of human rhinoviruses makes them a very difficult target to hit. A drug or a vaccine
that attacks one protein on the surface of one strain may prove to be useless against others that have a
version of that protein with a different structure. If another strain of human rhinovirus is even a little
resistant to such treatments, natural selection can foster the spread of new mutations, leading to much
stronger resistance.
Despite the diversity of rhinoviruses, some scientists are optimistic that they can develop a cure for
the common cold. The fact that all strains of human rhinoviruses share a common core of genes
suggests that the core can’t withstand mutations. In other words, viruses with mutations in the core
die. If scientists can figure out ways to attack the rhinovirus core, they may be able to stop the
disease. One promising target is a stretch of genetic material in rhinoviruses that folds into a loop
shaped like a clover leaf. Every rhinovirus scientists have studied carries the same clover-leaf
structure, which appears to be essential for speeding up the rate at which a host cell copies rhinovirus
genes. If scientists can find a way to disable the clover leaf, they may be able to stop every cold virus
on Earth.
But should they? Human rhinoviruses certainly impose a burden on public health, not just by
causing colds but by opening the way for more harmful pathogens. But the human rhinovirus itself is
relatively mild. Most colds are over in a week, and 40 percent of people who test positive for
rhinoviruses suffer no symptoms at all. In fact, human rhinoviruses may offer some benefits to their
human hosts. Scientists have gathered a great deal of evidence that children who get sick with
relatively harmless viruses and bacteria may be protected from immune disorders when they get
older, such as allergies and Crohn disease. Human rhinoviruses may help train our immune systems
not to overreact to minor triggers, instead directing their assaults to real threats. Perhaps we should
not think of colds as ancient enemies but as wise old tutors.