Modelling nuanced interventions for neglected tropical diseases

The majority of the World Health Organization (WHO) guidelines for control or elimination of neglected tropical diseases (NTDs) involve broad recommendations. There is some variation in these guidelines according to factors such as the co-endemicity of other diseases or failure to hit targets, but largely the same methods are used across a diverse range of cultures and climates. As the majority of NTDs have life-cycles that involve free-living stages or intermediary hosts, environmental conditions and external factors have the potential to either benefit or undermine the efforts of interventions. Through models we can explore the effect the varying biological parameters and simulate the outcomes of different types of interventions. This thesis aims to investigate a few of the current knowledge gaps by developing novel models of these processes for two specific diseases: Ascaris lumbricoides, a soil-transmitted helminth infection, and lymphatic filariasis (LF), a long-lived worm transmitted by mosquitoes. Extending established models from the literature, the work presented attempts to better describe some of the biological processes influencing transmission and the impact this could have on control and elimination strategies. A seasonal model of Ascaris infection is used to quantify the impact of fluctuations in external larval stage development on mass drug administration success, finding that the impact of seasonal variance is highly dependent on local weather profiles. Models of LF, considering both stochastic elimination and the vector dynamics, demonstrate the importance of solid experimental evidence for parameterising models and highlight why adult-acting vector control measures are potentially more effective than larval-based methods. Additionally, the vector model for LF is then used to recommend a novel method for deriving human prevalence estimates through vector sampling, including confidence interval and sample size calculations. This work has demonstrated new methods for modelling helminth infections in humans and drawn some important conclusions that could impact future studies and public health strategies for NTDs. By challenging modelling assumptions and realising what we don’t know, this thesis has lead to a deeper understanding of the processes involved and highlighted where further research is required.