Recently discovered human coronaviruses.

In marked contrast to their historical classification as relatively harmless, common cold-causing, respiratory pathogens, human coronaviruses (HCoVs) are associated with more severe clinical complications, as emphasized by the discovery of severe acute respiratory syndrome-associated CoV (SARS-CoV) in 2003. Still, their precise pathogenic potential is largely unknown, particularly regarding the most recently identified strains HCoV-NL63 and HCoV-HKU1, and definite proof for their etiology remains a major challenge. This article focuses on the characteristics of the five HCoVs that are known, and summarizes current knowledge of their pathogenic potential in people, with an emphasis on the interactions between these viruses and their cognate receptors on susceptible target cells.