Abstract
The relevant published literature concerning the nature of herpes simplex virus and its growth in fertile hens' eggs was reviewed. Laboratory strains and fresh isolates of types 1 and 2 were grown on the chorioallantoic membrane of fertile hens' eggs and examined by biological, histological and ultra-structural techniques. The type 1 strains induced small discreet pocks, gave no haemorrhage of the chorioallantoic membrane, or embryo, embryos did not die and virus was recovered only from the inoculated membrane. Similar inoculation with the type 2 strains induced large necrotic pocks and haemorrhage of the chorioallantoic membrane as well as haemorrhage and death of the embryo; virus was recovered from the inoculation site, allantoic fluid, amniotic fluid and various selected organs of the embryo. Inoculation of either virus type into the allantoic cavity did not result in spread to the embryo. The effects of adaptation to growth in eggs were examined. Temperature marker tests in eggs showed that fresh isolates of type 1 grew less readily on the chorioallantoic membrane at elevated temperatures than those of type 2. There was no difference in the capacity of laboratory strains of either type to grow in eggs at these temperatures. Primary chick embryo fibroblasts and other egg-derived cell cultures were used to examine the growth characteristics of a strain of each virus type; the results obtained in vitro could not be entirely predicted from those in ovo. The structure of the chorioallantoic membrane and the lesions produced by each virus type following inoculation were examined by optical and electron microscopy. The type 1 induced lesion was basically proliferative and confined primarily to the chorion with some inflammatory cell infiltration into the mesoderm, particularly following prolonged incubation. With the type 2 lesion, reaction occurred throughout the entire thickness of the membrane and haemorrhages, necroses, ulceration and cellular infiltration of the mesoderm were the most prominent features. The fine structure of the herpesvirus lesions and of viral morphogenesis was examined. Inoculation with type 2 virus resulted in many more infected chorion cells compared with type 1, whilst the cells of the mesoderm and the blood vessels also became infected with type 2 virus but not type 1. Features specific to type 2 virus infected cells were the presence of two types of intra-nuclear granules and lattice structures in both nuclei and cytoplasm. Cores with various structured forms were also found in type 2 capsids but not in those of type 1. The results of this study were discussed in relation to other published work.