Until the late 1960s, the coronaviruses were not recognized as pathogens responsible for human diseases (common cold). However, in 2003 human coronaviruses (HCoVs) came to worldwide attention with the emergence of the Severe and Acute Respiratory Syndrome (SARS), produced by a coronavirus (SARS-CoV) that infected more than 8000 people, killing about ten percent of them in 32 countries. The increase in research on coronaviruses soon led to the discovery of another human coronavirus (HCoV-NL63) which is prevalent in 7 per cent of hospital patients and has been associated with bronchiolitis and, possibly, conjunctivitis.