Characteristics of the Marek’s Disease Agent in Cell Cultures

An experiment was conducted to study the morphologic and biologic characteristics of the Marek’s disease agent (JM strain) in cell cultures. Very consistent cytopathic changes were noticed in CK cell cultures inoculated with JM blood and in CK monolayers derived from experimentally infected M.D. chickens. The changes which followed a definite sequence of events were characterised by the appearance of clusters of highly refractile starry cells, looking homogeneous and dark in stained preparations. Multinucleated giant cells and intranuclear inclusions were often associated with the focal lesions. Subsequently, the morphologically altered cells in the micro-lesions tended to fall off forming microplaques. A perfect correlation between the induction of cytopathic effect (CPE) and viral infectivity in JM cultures was noticed on experimental transmission in Cornell S-line chickens and subsequent reproduction of CPE in kidney cell cultures from the inoculated birds. The infectivity of cultures was maintained through successive passages in vitro. The chicken and duck embryo cell cultures inoculated with JM blood yielded inconsistent CPE. The negative staining technique of electron microscopy failed to demonstrate the virus in JM cultures that showed characteristic cytopathic changes and biologic activity of M.D. This was attributed to low level of infection or to yet unexplained intracellular properties of M.D. virus in cell cultures. The results showed that the M.D. virus-CK cell culture system was a useful tool for the development of in vitro bioassay procedure.