The effect of mitomycin C treatment of infected erythrocytes on infection with Babesia microti and Babesia rodhaini in mice

In vitro treatment of Babesia microti infected erythrocytes with mitomycin C before their injection into mice prolonged the prepatent period of infection, reduced the levels of the infection in the ‘breakthrough’ parasitaemia and induced protection against reinfection. Treatment of B. microti with mitomycin C at a concentration of 25 μg ml^?1 resulted in a mean peak parasitaemia of 6.2% in the infected mice compared with 46.5% in control mice injected with untreated B. microti parasites. In addition, mice survived a normally fatal B. rodhaini infection if injected with 6.2 × 10⁷ infected erythrocytes treated with 25 μg ml^?1 mitomycin C and four of five mice survived infection with 6.2 × 10⁵ similarly treated infected erythrocytes. However, the degree of protection against B. rodhaini was dependent on the concentration of mitomycin C used to treat the parasites and treatment of 5 × 10⁷ infected erythrocytes with 50 μg ml^?1 resulted in survival of only four of the five infected mice. In addition, when 100 μg ml^?1 of mitomycin C was used to treat B. rodhaini parasites, the course of infection, although delayed, was indistinguishable from that seen in the control mice and all the mice died. The latter results and the lack of efficacy of comparable numbers of heat killed parasites suggested the necessity for sufficient, non-replicating, mitomycin C treated parasites to metabolize and produce and/or present protective antigens to the host.