Schistosomiasis Models

As part of the NTD Modelling Consortium two world-leading institutions funded by Children's Investment Fund Foundation (CIFF) started to work along each other developing two separate models for each species of schistosoma. The teams are looking at what combination of interventions are needed to effect local elimination for Schistosoma heamatobium and Schistosoma mansoni in different contexts.

The schistosomiasis modelling groups are the internationally leading groups in modelling this disease, led by Professor Roy Anderson, Imperial College London and Prof Charles King, Case Western Reserve University in collaboration with Prof Alison Galvani, Yale University.

The London group has developped age group-based and fully age structured models of mean host worm burden dynamics, accounting for parasite aggregation, sexual reproduction, density-dependent fecundity and immunity to model the effect chemotherapeutic and WASH-based interventions. Additionally, an individual-based stochastic model with age and spatial structure provides a detailed simulation of host heterogeneity and variability, and facilitate the study of systematic non-compliance. Inclusion of immature worm stages allows the effectiveness of double treatment to be investigated. Bayesian inference is used to extract baseline worm burden distributions and key parameter values from shared data sources. Associated uncertainties in baseline burdens and parameters give realistic confidence intervals to be applied to predicted outcomes for 2020 and allow meaningful comparison with results from the CWRU-Yale group.

The CWRU-Yale team implement their extended distribution-free Stratified Worm Burden model calibrated against field data for S. mansoni, S .haematobium and S.japonicum using similar Bayesian techniques, to project treatment, control and potential elimination outcomes for regular or syncopated MDA, as well as integrated programs utilizing optimized seasonal snail control and WASH-E interventions.

As first outcome of this three-year project the two modelling groups have published their first results in October 2015 in a special collection of Parasites and Vectors.