The epidemiology of Schistosoma mansoni: Analysing the influence of current water contact, safe water supplies, and human mobility in rural Uganda

Thesis

BACKGROUND: Schistosomiasis is a waterborne parasitic disease that affects 250 million people globally, more than 90% of whom live in sub-Saharan Africa. Human behaviour is a key influencing factor of local transmission dynamics yet remains poorly understood, with existing research being reliant on aggregate mobility data and self-reported water contact without validated measurement tools to study exposure behaviour. This thesis uses detailed individual-level survey, GPS logger, and direct observation data to characterise the influence of current human water contact behaviour, mobility, and access to safe water supplies on the epidemiology of Schistosoma mansoni with a focus on rural Uganda. Here, current water contact is defined as engaging in any water contact within the past year or more frequently.

METHODS: Chapter 2 presents a systematic review and meta-analysis of 101 studies covering 192,691 participants, which examines the relationship between current water contact and schistosome infection likelihood. Chapter 3 presents an analysis of water contact patterns in the SchistoTrack cohort (n = 2867) in Uganda, employing Bayesian variable selection and multivariable logistic regression. Chapter 4 utilises GPS loggers from 452 SchistoTrack participants to build spatial decay models for predicting water site usage patterns, with a focus on the influence of human mobility and safe water supplies.

RESULTS: Chapter 2 found that individuals with current water contact had 3.14 times higher odds of schistosome infection compared to those without contact, and that associations varied based on climate. Chapter 3 identified older age, fishing occupations, proximity to multiple water sites, and village- level infection prevalence as key determinants of water contact. There was a strong age and gender dependence in water contact with minimal correlation between current water contact and infection. Chapter 4 developed spatial decay models that predict water site and tap usage with high accuracy and suggested that the presence of safe water infrastructure (taps/boreholes) could reduce water site usage by up to 10% and the duration of open water contact by up to 31%.

SIGNIFICANCE: This thesis offers insights into the role of human behaviour for schistosomiasis; it challenges the assumption that current water contact is necessarily a strong proxy indicator for infection status. It highlights the strong spatial concentration of water contact among individuals living near water bodies and exponential distance decays in water contact. Generalisable models are provided that predict water site usage to aid future intervention targeting and evaluation for the provision of safe water supplies. These findings are anticipated to inform the improved integration of behavioural factors into transmission models and guide future exposure measurement in control programmes.

Authors: Reitzug, F

• DOI: 10.5287/ora-brvb1ezyq
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Schistosomiasis; Uganda; water contact behaviour; Lake Albert; GPS loggers; human mobility; and hygiene (WASH); Lake Victoria; Schistosoma mansoni; spatial decay models; safe water access; sanitation; water
• Subjects: Parasitic diseases; Public health; Diseases--Epidemiology