The interaction of Babesia caballi kinetes with tick cells

Babesia caballi caused pathological changes in the vector tick, Anocentor nitents. These included the loss of hemocytes, reddish-brown discoloration of the hemolymph, retardation in clotting, and reduction in egg production. Primary cultures were initiated from A. nitens embryos transovarially infected with B. caballi. Cell lines that were isolated were morphologically similar and composed of stellate, fusiform, and hemocyte-like cells, but none was visibly infected with B. caballi. Primary cultures from heavily infected ticks were not viable and did not develop into lines. Kinetes from hemolymph and organs of A. nitens were cocultivated with cell lines isolated from embryos of A. nitens, Rhipicephalus appendiculatus, and Rhipicephalus sanguineus. They attached to and actively penetrated the cells. Cells that were penetrated by or infected with B. caballi showed rounding off, degeneration, and lysis. In Giemsa-stained spreads prepared after 1 or 2 days in vitro, more kinetes were associated with R. appendiculatus cells when the medium contained A. nitens egg extract (TEE). Ninety percent of the B. caballi kinetes were always found within or in close contact with cells from A. nitens, cultured with or without TEE. The parasites were club shaped, amoeboid, or round. Intracellular Babesia were frequently lying adjacent to the host cell nucleus. In the cultures the parasites were detected by light microscopy for 3 to 5 days; they did not transform into other tick-associated stages and were not seen after 1 week. This is the first report of the cultivation of tick stages of B. caballi in tick cell cultures.