In vitro infectivity of cryopreserved Plasmodium berghei sporozoites to cultured cells.

Plasmodium berghei sporozoites frozen in MEM (Eagle) medium supplemented with 10% hydroxyethyl starch and 50% normal mouse serum retained 0.5% infectivity to cultured hepatoma cells, compared to 6.8% before freezing. This demonstrates that frozen-thawed sporozoites can be used in in vitro investigations of the exoerythrocytic malarial parasite and means that when large numbers of sporozoites are available, they may be frozen and preserved for later use.