CHRONOLOGICAL STUDY OF ULTRASTRUCTURAL-CHANGES IN THE PERIPHERAL-NERVES IN MAREKS-DISEASE

Chronological study of ultrastructural changes in the peripheral nerves in Marek's disease A chronological study was made of the ultrastructural changes in peripheral nerves following inoculation of 1‐day‐old chicks with a neurogenic strain of Marek Disease virus. No virus particles were found in nerves. Cellular infiltration of nerves was detected as early as 5 days after inoculation and by 3 weeks some nerves contained proliferative lesions which possessed many of the ultrastructural features characteristic of normal, reactive lymphoid tissue. About 4 weeks after inoculation, coinciding with the onset of neurological signs, areas of widespread demyelination appeared within these lesions; lymphocytes and macrophages penetrated and destroyed the myelin sheath, but spared Schwann cells and most axons. Later oedematous, sparsely infiltrated B type lesions were observed, some of which contained demyelin‐ated nerve fibres undergoing repair; these were therefore a stage in the regression of the proliferative lesions. Our observations do not favour the hypothesis that cellular infiltration of nerves in Marek's disease is the direct result of auto‐sensiti‐zation to normal myelin. They are consistent with the hypothesis that demyelination is a secondary feature and that the primary lesions are preferential sites for immune demyelination. Copyright © 1979, Wiley Blackwell. All rights reserved