Cryopreservation of Babesia divergens from jirds as a live vaccine for cattle.

A Babesia divergens live vaccine can be produced in jirds (Meriones unguiculatus). The major drawback of this live vaccine is the short shelf-life. We evaluated different methods for the cryopreservation of this vaccine. Blood from jirds infected with B. divergens was frozen to -196 degrees C using cooling rates of 1, 10, 30, 100, 196 and 250 degrees C min-1, and a two-step cooling rate. The cryoprotectants dimethyl sulfoxide (DMSO), polyvinylpyrrolidone 40 and glycerol were used at different concentrations. Aliquots were stored in liquid nitrogen for 10-20 days and rapidly thawed in a water bath at 40 degrees C. Infectivity of blood before and after cryopreservation was tested in jirds by i.p. inoculation. The prepatent periods recorded were used to calculate the infectivity of the inocula. The highest infectivity of 46% was recorded from blood cryopreserved with 3 M DMSO and cooled at 10 degrees C min-1. Infectivity of the frozen vaccine was tested in 4 heifers by inoculation of 2.5 x 10(7) parasites. All animals showed Ab titres 12 days after inoculation.