In vitro responses of praziquantel-resistant and -susceptible Schistosoma mansoni to praziquantel

The resistance status of five praziquantel-susceptible and five praziquante l-resistant isolates was confirmed by chemotherapy in CD1 mice with 3 X 200 mg/kg micronised praziquantel. Micronised praziquantel had higher efficacy than two other praziquantel formulations (prepared without milling). The f ive resistant isolates were less responsive to praziquantel than the five s usceptible isolates (59-74% reduction in worm burden in resistant isolates compared with 92-100% in susceptible isolates). Observations were made on t he in vitro responses of different stages of 10 isolates to praziquantel. T here were different in vitro responses to praziquantel at the egg, miracidi al, cercarial and adult stages of Schistosoma mansoni between praziquantel- resistant and praziquantel-susceptible isolates. There were differences in the response of resistant and susceptible isolates following exposure of fr eshly hatched miracidia to 10(-6) M praziquantel for 1 min and observing th e percent change in shape. Using this test it should be possible to determi ne whether failed therapy in patients infected with S. mansoni is due to th e presence of praziquantel-resistant worms. Similarly, by exposing freshly shed cercariae to 4 X 10(-7) M praziquantel and observing the percent of ta il shedding over 80 min it should be possible to monitor for the presence o f praziquantel-resistant worms in snails collected in the field. (C) 2001 A ustralian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.