Demonstration of 7-nm projections on human and avian coronaviruses

Direct electron microscopy (EM) of human coronavirus (HCV) strain OC43 and avian infectious bronchitis virus (IBV) strain F revealed particles with small granular projections about 7 nm in size in addition to the characteristic coronavirus particles with projections of 20 nm. Relationship of the short fringed form to the conventional coronavirus particle is established by ordinary immune electron microscopy (IEM) and immunosorbent electron microscopy (ISEM).