Cytopathology caused by the AC-1 isolate of Marek's disease virus in the feather follicle epidermis

The AC-1 strain of Marek's disease herpesvirus (MDV), recently isolated from an outbreak of Marek's disease in vaccinated chickens, was used for intraperitoneal inoculation of one-day-old Single Comb White Leghorns. Chicks were necropsied 12 to 32 days post inoculation and skin was collected for electron microscopic studies. This paper focuses on early stages of MDHV development in feather follicle epithelial cells and on cytoplasmic changes that occur in formation and release of virus particles. In some nuclei we observed helical threads of DNA which were partially encircled by capsid membranes. This was interpreted to be an early stage of nucleocapsid development. In the infected epidermal cells, the smooth endoplasmic reticulum vesiculated and appeared to be hyperplastic. Immature virus particles released into cytoplasm acquired their outer envelope while budding into cytoplasmic vesicles. Vesicles containing mature viruses were referred to as cytoplasmic vesicular inclusions. It appeared that the degenerative process in cells facilitated the release of virions from the feather follicle epithelium.