Loss of resistance to reinfection with Schistosoma japonicum in mice after treatment with praziquantel

Abstract

Seven-week-old adult Schistosoma japonicum worms were eliminated from mice within one week of treatment with praziquantel and oviposition ceased within 2 days. The excretion of faecal eggs ceased within 2 weeks of treatment. The numbers of eggs retained in the intestine and those in the liver remained constant for up to 20 weeks after cure. Untreated, infected mice were on average 80% resistant to reinfection and mice challenged one week after treatment were equally resistant. However, reductions in the ability of mice to resist a challenge were evident as early as 2 weeks after cure (average resistance 40%) and by 5 weeks the resistance had dropped significantly (average resistance 30%) in all experiments. Mice were no longer significantly resistant to challenge 13 weeks after treatment, in 2 out of 3 experiments. It is suggested that the reduced ability of cured mice to resist reinfection is related to the resolution of the granuloma response and associated pathology rather than the loss of tissue eggs.