In ovo assay for Marek's disease virus and turkey herpesvirus.

Marek's disease virus (MDV) and the turkey herpesvirus (HVT) may be assayed on the chorioallantoic membrane (CAM) of the chicken embryo after intravenous inoculation of chicken embryo fibroblasts (CEF) or chicken blood leukocytes infected with these viruses. Free HVT, MDV associated with Marek's tumor cells, and lymphoblastoid cell lines derived from Marek's tumors, may be assayed in the same way. The intravenous assay is quicker than the yolk sac assay and somewhat more sensitive than in vitro or conventional CAM assay after direct inoculation of the CAM. The optimal time for inoculation was day 10 of embryo incubation; therafter the log-10 CAM lesions decreased as a negative linear function of embryo age at the time of inoculation. The log-10 CAM lesions increased as a positive linear function of the time since inoculation. The optimal time for counts was day 5 after inoculation. The log-10 CAM lesions was a linear function of the log-10 cells in the inoculum; the slope was 1.0. Venous in ovo inoculation caused as increase in the weight of the spleen proportional to the number of CAM lesions. Repression of the splenomegaly, by prior X irradiation of the embryo, did not reduce the number of CAM lesions. Embryols from lines inbred for susceptibility to Marek's disease produced more CAM lesions than embryos from resistant lines. This difference did not depend on prior exposure of the mothers to MDV or HVT.