Effects of passive antibody on early pathogenesis of Marek's disease.

The effects of passive Marek's disease virus (MDV) antibody were characterized in three experiments in which 1- or 2-day-old PDRC chickens were inoculated with cell-associated MDV. Antibody acquired naturally from the dam, or injected prior to, or at the time of, virus inoculation, failed to prevent infection, but the incidence and severity of the acute necrotizing disease were reduced. Also, the number of tissues with viral antigen (fluorescent antibody test) and the amount of antigen in positive tissues was lowered, and fewer infected cells in spleen (in vitro assay) were detected in antibody-positive chicks. Serum containing MDV antibody was efficacious when injected prior to infection and had some protective effect when first given at day 4 but not at day 7 after virus inoculation. Normal antibody-free serum was ineffective, and chickens with naturally acquired (maternal) antibody against turkey herpesvirus (a virus antigenically related to MDV) were not protected against MDV infection.