Establishing a single-sex controlled human Schistosoma mansoni infection model for Uganda: protocol for safety and dose-finding trial

Abstract

Control of Schistosomiasis depends on a single drug, praziquantel, with variable cure rates, high reinfection rates and risk of drug resistance. A vaccine could transform schistosomiasis control. Preclinical data show that vaccine development is possible, but conventional vaccine efficacy trials require high incidence, long-term follow-up and a large sample size. Controlled human-infection studies (CHI) can provide early efficacy data, allowing selection of optimal candidates for further trials. A Schistosoma CHI has been established in the Netherlands, but responses to infection and vaccines differ in target populations in endemic countries. We aim to develop a CHI for Schistosoma mansoni in Uganda to test candidate vaccines in an endemic setting. This is an open-label, dose escalation trial in two populations: Minimal, or intense, prior Schistosoma exposure. In each population, participants will be enrolled in sequential dose-escalating groups. Initially, three volunteers will be exposed to 10 cercariae. If all show infection, seven more will be exposed to the same dose. If not, three volunteers in subsequent groups will be exposed to higher doses (20 or 30 cercariae) following the same algorithm, until all 10 volunteers receiving a particular dose become infected, at which point the study will be stopped for that population. Volunteers will be followed weekly after infection until CAA positivity or to 12 weeks. Once positive, they will be treated with praziquantel and followed to one year. Trial registry number is ISRCTN14033813 and all approvals have been obtained. The trial will be subjected to monitoring, inspection and/or audits.