Isolation and propagation of coronaviruses in embryonated eggs.

The embryonated egg is a complex structure comprised of an embryo and its supporting membranes (chorioallantoic, amniotic, yolk). The developing embryo and its membranes provide the diversity of cell types that are needed for successful replication of a wide variety of different viruses. Within the family Coronaviridae the embryonated egg has been used as a host system primarily for two avian coronaviruses within the genus Gammacoronavirus, infectious bronchitis virus (IBV) and turkey coronavirus (TCoV). The embryonated egg also has been shown to be suitable for isolation and propagation of pheasant coronavirus, a proposed member of the Gammacoronavirus genus. IBV and pheasant coronavirus replicate well in the embryonated chicken egg, regardless of inoculation route; however, the allantoic route is favored as these viruses replicate well in epithelium lining the chorioallantoic membrane, with high virus titers found in these membranes and associated allantoic fluids. TCoV replicates only in epithelium lining the embryo intestines and bursa of Fabricius, thus amniotic inoculation is required for isolation and propagation of this virus. Embryonated eggs also provide a potential host system for detection and characterization of other, novel coronaviruses.