INITIAL LESIONS IN CHICKENS INFECTED WITH JM STRAIN OF MAREK'S DISEASE VIRUS

Severe lymphoid degeneration and hyperplasia of the reticular and epithelial components were present in the lymphoid tissues on the 6〜8th day after inoculation of JM strain of Marek's disease virus (MDV). At the same time, intranuclear and cytoplasmic inclusions with many virus particles were frequently found in these components of the lymphoid tissues (the bursa of Fabricius and thymus). Inaclusions were also observed in the epithelial cells of the pancreas, adrenal glands, kidneys and feather follicles. Two types of enveloped virus particles were found in adrenal cells and the feather follicle epithelium (FFE). Inoculated chickens were free from precipitating antibodies to MDV through a 48 day observation period. Immunofluorescent (IF) antigen was first detected in the thymus and lungs (8th day). MDV was demonstrated to exist by kidney cell cultures from the 8th day postinoculation. Microscopic lesions characteristic for MD were seen on and after the 12th day postinoculation. In contact-exposed chickens, there were no remarkable changes in the lymphoid tissues at the early stage of the disease. Thereafter inclusions could not be found in any tissues, except the skin and lungs. Precipitating antibodies to MDV were detected from the 60th day postexposure. IF antigen was detected in the thymus and FFE (23rd day). MDV was demonstrated to exist and microscopic lesions were seen on and after the 32nd day postexposure