Evaluation of inhibitory effect of redox-active antimalarial drug against Babesia microti in mice.

Babesiosis is an emerging, tick-transmitted disease caused by the intraerythrocytic parasite Babesia microti. In immunocompetent individuals, B. microti infection quickly resolves after antibabesial treatment. Immunocompromised patients and those of advanced age experience chronic and relapsing babesiosis, accompanied by severe complications and often, a fatal outcome. In these individuals, B. microti infection may persist despite multiple courses of treatment with antiprotozoal drugs. The increasing incidence of human babesiosis caused by B. microti, coupled with a growing number of immunosuppressed people who do not respond to standard antibabesial therapy, emphasises the need for new therapeutics for this protozoan infection with more effective mechanisms of action. Plasmodione, namely 3-[4-(trifluoromethyl)benzyl]-menadione, acts as a redox cycler and disrupts the redox homeostasis of Plasmodium-infected erythrocytes. The present study was designed to evaluate the potential inhibitory effect of this novel antimalarial compound against intraerythrocytic stages of B. microti in mice. Our results demonstrate that plasmodione did not reduce the level of parasitemia in B. microti-infected mice, indicating that interfering with the parasite redox balance is not an effective strategy to restrict the division of this protozoan. The mechanism of parasite resistance to plasmodione may be based on the differences in the oxidative metabolisms of Babesia and Plasmodium parasites inside infected erythrocytes. The significance of our results is discussed in relation to the development of novel antibabesial drugs based on redox-active benzylmenadiones.