Recovery of infective Schistosoma mansoni schistosomula from liquid nitrogen: A step towards storage of a live schistosomiasis vaccine

Abstract
Successful recovery of infective schistosomula of Schistosoma mansoni following storage at −196 °C is reported. The technique involves a two-step cooling procedure—slow cooling (0.65 °C min−1) to an intermediate temperature of −28 °C, followed by rapid cooling into liquid nitrogen (10,000 °C min−1). Rewarming (10,000 °C min−1) and rapid dilution to remove the cryoprotectant (17.5% methanol) yielded motile organisms some of which developed to adult worms in mice after intramuscular injection. The percentage of schistosomula developing to adult worms was small (044%), but is a significant step towards storage of trematode larvae and of a live attenuated vaccine for schistosomiasis.