DEVELOPMENT OF TICK GUT FORMS OF BABESIA-BIGEMINA IN-VITRO

Development of a laboratory cultured tick-transmissible strain of Babe sia bigemina was followed in vitro after addition of gut material from engorged female Boophilus microplus ticks and incubation at 37 degree s C. Sequential development of stages, from intraerythrocytic strahlen korper through multiplication to the fusion of what is assumed to be t wo gametes, is described. A change in physical environment (temperatur e, gas composition) experienced during passage of Babesia stages into the in vitro culture tubes possibly mimics the changes experienced in passage from host blood to the midgut of the tick vector. The effect i n vitro was to induce the erythrocytic Parasites to remain inactive at a trophozoite-like stage. Addition of factor(s) within midgut initiat ed further development of strahlenkorper. Two populations of strahlenk orper were recognized; an elongated form which did not appear to devel op further, and a polymorphic population which underwent further multi plication initiated while the parasites were still within the erythroc yte, and continuing after they had emerged. These strahlenkorper incre ased in size as multiple division of nuclei occurred, with cell divisi on being completed more slowly. Large aggregations of multinucleated s trahlenkorper formed, but once division was complete, single-nucleated strahlenkorper emerged from the aggregates. Two individuals of post-a ggregation strahlenkorper, assumed to be gametes, fused together. The morphology and ultrastructure of all stages of development are describ ed and compared with forms already described from the tick midgut.