CENTRAL-NERVOUS-SYSTEM LESIONS INDUCED EXPERIMENTALLY BY A VERY VIRULENT-STRAIN OF MAREKS-DISEASE VIRUS IN MAREKS-DISEASE-RESISTANT CHICKENS

The histological lesions of central nervous system (CNS) in Marek's di sease-resistant chickens inoculated with a very virulent Marek's disea se virus strain (vvMDV), Md/5, were examined. This vvMDV induced high incidences of CNS lesions as well as visceral and peripheral nerve les ions. The principal histopathological changes of CNS consisted of non- suppurative meningoencephalomyelitis and lymphomatous lesion, which we re categorized into two types, non-necrotizing and necrotizing. The ma in changes in the former type were perivascular cuffing of lymphoid ce lls of variable thickness, Although diffuse lymphomatous lesions were sometimes observed, gliosis, neuronal and axonal degeneration, and sat ellitosis as well as demyelination in the myelinated fibre paths. were infrequent. The most significant change of the latter type was necrot izing lymphomatous and, sometimes, non-suppurative inflammatory lesion s (malacia), In the malacic foci, all the cells, including infiltratin g lymphoid cells, neurons and glial cells, were necrotic or degenerate d. The malacic lesions were frequently accompanied by fibrinoid necros is of blood vessels. The present results indicate that necrotizing vas culitis associated with vvMDV may lead to ischaemic damage which in tu rn induces necrotizing lymphomatous and sometimes, meningoencephalomye litis lesions. In addition, it is considered that vvMDV can induce a h igh incidence not only of CNS lesions, but also of visceral and nerve lesions in Marek's disease-resistant chickens.