In Vitro Experiments on the Viability and Excystment of Paragonimus Cyst

Abstract

Cysts were obtained from infected crabs (Potamon denticulatus Milne-Edwards) collected from Lan Ting, where the first 2 human cases of paragonimiasis in China were reported by Ying. Experiments were carried out in hollow glass slides in which actively motile encysted cercariae were placed in the medium to be tested. Freed cysts which had been kept in ice chest for 7 days could live in wine made from millet (Sorghum vulgare L.) in (a) 10% alcohol, for 43 hours at 22°C., and 20 hours at 37°C., (b) 25% alcohol, for 1 hour at 22C., and (c) 50% alcohol for a few seconds at the same temperature. In yellow rice wine with 14% alcoholic content, death took place in 18 hours at 22°C., and in 15 hours at 37°C. They could be kept alive in 10% formalin for 23 days and in 0.9% saline for a like period in the ice chest (10°C.). The metacercariae caused to excyst by the methods described in the next series of experiments were actively motile in trypsin 1% plus sodium carbonate 0.2% for at least 3 hours at 37°C. if bacterial growth was not checked and could remain dormant for 43 hours in the ice chest in the same medium. When they were placed alternately at 22°C. and at 16°C. they could live 84 hours. In 12% bile and in artificial intestinal juice plus bile (5%), their viability was 42 hours in the ice chest. These experiments demonstrate that in a diluted millet wine containing 10% alcohol and in rice wine (14% alcohol), the encysted metacercariae were viable up to 43 and 18 hours at room temperature (22°C), respectively, and that they could be kept alive in the ice chest (10°C.) in 10% commercial formalin or in 0.9% saline for over 3 weeks.