Comparison of cryoprotectants in the preservation of Theileria parva sporozoites using an in vitro infectivity assay

An in vitro infectivity assay was used to examine five cryoprotectants for their suitability for preserving Theileria parva sporozoites. All five were capable of preserving T. parva sporozoites through freezing, the optimal c oncentrations being 7.5% for glycerol, 5% for dimethyl sulphoxide (DMSO), p oly (vinylpyrrolidone) (PVP) and poly(ethylene glycol) (PEG), and 2.5% for hydroxyethyl starch (HES). When the five cryoprotectants were compared at t heir optimal concentrations, using a modification of the standard method of stabilate preparation, glycerol was significantly better than the others ( p <0.05). Measurement of the effects of each cryoprotectant on the osmolali ty of the media revealed that glycerol and DMSO elevated the osmolality sig nificantly (p <0.05). Resuscitation of glycerol-preserved sporozoites requi red the presence of glycerol in the diluent to maintain infectivity. Studie s on the effects of equilibration time in glycerol on the infectivity of sp orozoites showed that those frozen immediately after mixing (2 min) were as infective as those frozen after 60 min of equilibration.