© OCEAN/CORBISThe common cold is usually nothing more than a temporary nuisance. Except for people who are highly immunosuppressed or have other serious conditions, colds—most commonly caused by very small RNA viruses known as rhinoviruses—are usually restricted to the cells lining the upper respiratory tract and tend to be limited in duration and symptoms. Nevertheless, with a global population exceeding one billion trillion (1021), rhinoviruses are arguably the most successful rapidly infecting viruses on Earth today.
Despite their abundance, rhinoviruses have been relatively understudied by virologists and largely ignored by epidemiologists and virus modelers. Many mathematical methods for studying virus evolution and spread have provided key insights into the control of epidemics, but these efforts have concentrated on viruses such as HIV and influenza, and cannot be directly applied to the study of rhinoviruses. Unlike these more dangerous viruses, rhinoviruses did not jump recently from other animals to humans. They are human specialists that almost certainly evolved several times from the equally specialized enteroviruses that infect the gut. This means that rhinoviruses are highly adapted to humans, possibly explaining their low virulence—because they have had a chance to evolve efficient ways of spreading to many individuals without harming their hosts—and their ...
