Abstract
The morphogenesis of the vaccinia subgroup of poxviruses has been extensively examined using cell cultures and embryonated eggs (Joklik, 1966). However, Burnet (1955) pointed out that, at least for the formation of inclusion bodies, there is a marked difference between infected epithelial cells in vivo and cells infected in the laboratory. To clarify the structure and significance of poxvirus inclusions in vivo we have examined conventional and thin sections of pigeonpox lesions taken from a naturally infected bird. Sections of chorioallantoic membrane inoculated with the virus were examined for comparison.
Examination of the lesions in the pigeon by conventional microscopy showed that the epidermis was markedly thickened due to proliferation of stratified squamous cells. Single eosinophilic intracytoplasmic inclusions (Fig. 1) about the size of a cell nucleus or bigger were present in the majority of these cells. In contrast to the squamous cells, inoculated chorioallantoic membranes, although covered with pocks, had very few cells with recognizable inclusions; however, the few inclusions which were detected were similar to but much smaller than those seen in the original lesions.