Chapter 12 Coronaviridae.

Coronaviruses are spherical, lipid-containing, enveloped particles with tear-dropshaped surface projections or peplomers. The genome is one molecule of ssRNA and the virions characteristically contain three major structural protein classes. The antigenic relationships of coronaviruses present a complex pattern. The geographic distribution of many coronaviruses is worldwide. Biological vectors of coronaviruses have not been reported, and the natural hosts form the major reservoirs for further infection. Coronavirus particles contain three major protein classes, within which the polypeptides vary in number and molecular weight between species. The apparent size and shapes of coronaviruses can vary considerably. Coronavirus particles are spherical, although negatively stained air-dried particles are often pleomorphic. The morphology of coronavirus surface projections can vary considerably between different strains. The conventional structure on negative staining consists of tear-drop-shaped projections, although cone-shaped projections are also observed. In all these cases, the projections have the same length of about 20 nm. Other coronaviruses have short as well as 20-nm projections. Projections with blebs on thin stalks have been reported for other coronaviruses.