Cryopreservation of Babesia bovis for in vitro cultivation.

The most efficient procedure for cryopreserving viable Babesia bovis organisms for in vitro cultivation consists of freezing extracellular parasites in a solution of 10% (w/v) polyvinylpyrrolidone (PVP) using a cooling rate of 20 degrees C/min. Although cultures can be established from thawed infected erythrocytes, the plating efficiency is relatively low. Freezing extracellular parasites resulted in plating efficiency up to 25%, when thawed and placed in culture. Glycerin or dimethyl sulphoxide (Me2SO) can be used successfully in the cryopreservation of B. bovis but apparent toxic effects greatly decrease their efficiency. B. bovis parasites have been kept to -196 degrees C for 60 days with no appreciable reduction in plating efficiency.