Coronaviruses, a New Group of Animal RNA Viruses

In the last few years, strains have been isolated from various human common cold epidemics which resemble avian infectious bronchitis virus (IBV) so much, both morphologically and in other properties, that they have been called IBV-like viruses. It has also been found that the mouse hepatitis virus is morphologically identical with them. All these viruses seem to constitute a group of their own and are known to possess at least the following common properties: 1) size 80-160 m/; 2) characteristic surface structure; 3) sensitivity to lipid solvents; 4) ribonucleic acid content; 5) low density of infectious units (1.18-1.19 in sucrose gradient); 6) development in the cytoplasma by budding into cisternae or vesicles. The nucleocapsid structure of these viruses is still unknown. Because of the characteristic appearance, recalling the solar corona, the name coronaviruses has been suggested. Besides avian infectious bronchitis virus and mouse hepatitis virus, this virus group at present includes five IBV-like human strains: B814, 229E, OC43, LP, and EVS. Some comparisons in cross-neutralization tests have been made among the viruses of the group. The results showed that they all seem to belong to distinct serotypes. However, it was necessary to use several neutralization methods since no common method applicable to all the strains was available. Hence, conclusions based on those results must be treated with reserve. First, the adequate serological studies can disclose how closely related the viruses are and whether there is a speculative possibility that the IBV strains which are ubiquitous in almost all poultry populations can serve as reservoirs for human common cold infections, e.g. through mutation of IBV or hybridization of animal and human coronaviruses.