A quantitative long-term cryobiological study of malarial parasites.

A study spanning 10 years indicates that the erythrocytic stages of malarial parasites can be stored indefinitely in the vapour phase of liquid nitrogen without significant loss of infectivity. The results also suggest that loss due to the recovery procedures exceeds any loss that may have occurred during freezing and thawing. When feasible, large pools of material should be divided into smaller aliquots before storing the organisms at a low temperature, since freezing a second time produces significant losses of infectivity. Sporozoites and exoerythrocytic stages may be treated similarly, but the optimum conditions for freezing these forms have yet to be determined.