Babesia bovis: increased percentage parasitized erythrocytes in cultures and assessment of growth by incorporation of [3H]hypoxanthine.

Babesia bovis was established in continuous in vitro erythrocyte cultures using a modification of techniques developed previously. Using optimal conditions for maintaining continuous exponential growth, a threshold number of infected erythrocytes was obtained after which exponential growth ceased. However, at this level, individual parasite development continued resulting in a higher proportion of mature merozoite infected erythrocytes. Additionally, the percentage parasitized erythrocytes could be increased by reducing the concentration of total erythrocytes. Growth was assessed by determining the percentage parasitized erythrocytes and level of incorporation of [3H]hypoxanthine. Uninfected erythrocytes did not incorporate the radiolabeled purine while infected cultures incorporated it in direct proportion to the increase in percentage parasitized erythrocytes. Pulse labeling experiments indicated that the trophozoite form (the developmental stage prior to division that results in paired merozoites) incorporated the majority of this purine into nucleic acids.