A One Health Approach to Water as an Ecological Enabler for Leptospirosis: A System Dynamics Model

Leptospirosis is a neglected zoonotic disease of global importance and remains a persistent public health challenge in Fiji, where outbreaks frequently occur following extreme weather events. This study developed a One Health System Dynamics model to simulate interacting human, rodent, and environmental subsystems over a 24-month outbreak-relevant period, parameterised using published epidemiological and ecological data. Model validity and robustness were assessed through the reproduction of known epidemiological patterns, including seasonal trends. Results indicate that leptospirosis incidence is primarily driven by the interaction between rodent population dynamics and water systems, with standing water acting as a critical ecological enabler for both Leptospira persistence and rodent habitat suitability. Extreme scenario testing indicated that eliminating water contamination drove cases to near zero within 14 months, whereas soil contamination had minimal effect. Sensitivity analyses identified rodent birth and death rates as the most influential parameters governing system behaviour. While an integrated One Health intervention produced the greatest cumulative reduction in cases (21.07%), intervention effects were additive rather than synergistic, reflecting the dominance of underlying ecological feedback structures. This study offers a novel system-based framework for understanding leptospirosis burden in Fiji. It advances beyond static risk models by capturing endogenous dynamics, feedback loops, and non-linear interactions. The findings highlight the need for genuine cross-sectoral coordination and ecologically based rodent management near water bodies to sustainably reduce Fiji’s disease burden.