Adaptation and possible attenuation of Theileria parva-infected cells grown in irradiated mice

Abstract Theileria parva -infected bovine lymphoid cells were taken from 8 cattle immediately after death from East Coast fever (ECF). Cells were inoculated into groups of irradiated Swiss and athymic nude mice. Cells became established in one group of Swiss mice and 2 groups of athymic mice. Development of cells in mice only occurred if cells concurrently established in culture; when establishment in culture was delayed, cells failed to develop in mice. Cells from one of the isolates in athymic mice were passaged 6 times through further mice. On inoculation of these mouse-passaged cells into cattle, the animals underwent mild reactions and subsequently resisted a lethal ECF challenge. The possibility of vaccinating cattle against ECF by means of mouse passaged cells merits further study.