The sting of Theileria annulata

Abstract

Tropical theileriosis is caused by the protozoan parasite Theileria annulata and affects cattle from the Mediterranean to China. The parasite, which is transmitted by ticks, infects leukocytes to form macro- and microschizonts – microschizonts produce merozoites that can infect red blood cells. To control the disease, live attenuated vaccines consisting of leukocyte-resident macroschizont stages of the parasite are being used with variable success. The process of attenuation is not clearly understood and the safety and efficacy of such lines can only be determined by vaccination–challenge experiments. Researchers have now found a correlation between the effects of T. annulata on the host-cell cytokine-expression pattern and the safety of attenuated parasite lines [Graham, S.P. et al. (2001) Vaccine 19, 2932–2944]. Cloned parasite-infected cell lines that express relatively low amounts of proinflammatory cytokines are as effective as those expressing high amounts of these cytokines in inducing protective immunity in cattle. More importantly, when used to vaccinate cows, the parasite-infected cell lines expressing low levels of cytokines were significantly safer than their counterparts expressing high cytokine levels. TS