Interest in the coronaviruses has never been greater. Their economic impact is considerable as they infect humans, livestock, poultry and companion animals. Murine hepatitis virus (MHV) infection of the mouse and rat central nervous systems are the subject of intense study; these investigations are providing insights into the potential role of viruses in human neurological diseases and, more generally, into mechanisms causing neurological damage. The single-stranded, positive-sense RNA genomes of two species of these enveloped viruses (IBV and MHV) have been cloned completely and one of them...