Propagation and behavior in chicken kidney cultures of the agent associated with classical marek's disease

A classical isolate (WSU-GF) of Marek's disease herpesvirus (MDHV), isolated from the kidneys of a chicken with clinical symptoms of the disease, was successfully propagated in chicken kidney (CK) cultures. The cytopathic effect (CPE) was similar to that produced by the herpesviruses of group B and could be inhibited by 5-iododeoxyuridine. With continued serial passage of MDHV in CK cultures, the character of CPE was changed in that the polykaryocytes became much larger and the type-A inclusions more frequent. Based on the specific CPE, a tissue culture assay system for MDHV was standardized. It was found that a cell was the unit of infection. A pH of 7.5 and an incubation temperature of 37°C in CO₂ atmosphere were optimal for the expression of CPE by MDHV. A minimum contact of 12 hours was necessary between the infected and the normal CK cells to obtain a maximum number of foci of infection. It appeared that the cells of infected cultures became infectious before attaining a rounded, refractile state.