A simple in vitro differentiation between turkey herpesvirus and Marek's disease virus

The growth and plaque formation by turkey herpesvirus (HVT) amd Marek's disease herpesvirus (MDHV) were examined in QT35 cells, a continuous fibroblast cell line derived from chemically induced tumors of Japanese quail. HVT grew and formed plaques consistently in QT35 cells when inoculated with cell-culture-propagated virus or peripheral mononuclear leukocytes (PML) from chickens that had been inoculated with HVT. Both oncogenic and nononcogenic strains of MDHV, however, failed to grow and induced neither plaques nor cytopathic effects in QT35 cells, whether inoculated with cell-culture-grown virus or heavily infected PML. When PML from chickens infected with both HVT and MDHV were assayed, only HVT plaques had developed, despite the presence in the inocula of high levels of MDHV with less HVT. The QT35 cell line provides a simple in vitro system for differentiating between HVT and MDHV and for selective isolation and identification of HVT from chickens infected with both HVT and MDHV.