Etiologic relationship of skin tumors (Skin leukosis) of chickens to marek’s disease

Chicken kidney (CK) cell cultures, inoculated with homog­enates of grossly visible skin tumors of the chicken, developed a cytopathic effect (CPE) similar to the CPE of the Marek’s disease herpesvirus. Electron microscopic examination of the infected CK cultures revealed herpes virions.The CPE of this virus could be inhibited by 5-iododeoxyuridine, and the virus remained strictly cell associated. Disruption of infected cells by 3 cycles of quick freeze-thawing (in dry ice-alcohol and 37°C water bath) destroyed the infectivity. Suspensions of infected CK cells, negative for resistance-inducing factor, were inoculated into susceptible chickens. A disease picture typical of acute Marek’s disease (MD) was produced, and 3 of 10 inoculated chickens developed gross skin tumors. The virus could be isolated from the kidney and skin homogenates of experimentally infected chickens. It is suggested that the skin tumors of the chickens studied are a part of the MD syndrome and that the term "skin leukosis’’ designated to them is misleading.