Simulation in vitro of bovine host cycle of Theileria parva.

Abstract

Theileria parva is a tick-transmitted parasite causing East Coast fever in cattle. Research on T. parva has been impeded because of difficulties in completing the mammalian part of its life cycle in any non-bovine host. Several attempts to adapt the organism to small laboratory animals have failed1–5. Limited success was reported by Irvin et al.6,7 using whole-body irradiated nude athymic mice. Many attempts to cultivate the parasite in vitro also failed8–12 until Malmquist et al.13 were successful using suspension cultures of infected bovine lymphoid cells which eventually contained the macroschizont form in the cytoplasm—the relationship between bovine lymphoid cell and parasite makes the perpetuation of both possible in a suitable culture medium. This led to further research into the development of an artificial immunogen and studies of the macroschizont stage of the life cycle without recourse to the bovine host. So far, however, tissue culture methods have not produced all stages of the parasite subsequent to the macroschizont; namely microschizonts, micromerozoites and piroplasms. The final stage, which is intraerythrocytic, is believed to be of crucia ilmportance in initiating the separate cycle which occurs in the tick vector (Rhipicephalus appendiculatus).