Long-term storage of Clonorchis sinensis metacercariae in vitro

Clonorchis sinensis metacercariae must often be stored for several months to meet laboratory requirements. In the present study, the authors evaluated morphological changes and infectivities of metacercariae kept in different storage solutions for 1, 3, and 6 months, i.e., PBS (phosphate buffered saline), PBS + antibiotics, PBS + iodoacetic acid (IAA), and PBS + antibiotics + IAA. Metacercariae stored in PBS containing antibiotics showed significantly higher survival rates and infectivities than those stored in PBS alone after 3 or 6 months. The metacercariae that had been stored for 6 months in solutions that were refreshed monthly had also significantly higher survival and infection rates than those stored in nonrefreshed solutions. Moreover, the addition of IAA, an inhibitor of cysteine proteinase, to these storage solutions reduced the survival and infectivity. The results of the present study confirm that the viabilities of C. sinensis metacercariae are best maintained in storage solutions containing antibiotics that are regularly refreshed.