SNF Opisthorchis Modelling - Mathematical modeling of transmission dynamics of Opisthorchis viverrini
Project Abstract
Background
The trematode liver fluke, Opisthorchis viverrini causes the chronic and debilitating hepatobiliary disease, opisthorchiasis, which can lead to the fatal bile-duct cancer, cholangiocarcinoma. About 8 million people are infected with O. viverrini, mostly in Thailand, Laos and Cambodia with a further 80 million at risk. O. viverrini exhibits a complex life cycle involving humans and reservoir mammalian hosts (such as dogs and cats), free-swimming aquatic stages, and intermediate host stages in faucet snails and cyprinoid fish. Humans get infected through the consumption of raw or undercooked infectious fish. The role of reservoir hosts in transmission dynamics is poorly understood but believed to be important. Control is currently based on treatment, health education on food consumption, and improved sanitation. However despite more than 20 years of control activities, prevalence remains high in foci of northeastern Thailand. In the absence of long-term control, prevalence is even higher in Laos, exceeding 60% in high endemic provinces. Large-scale control has recently started in Laos, so there is a pressing need to understand the effectiveness and cost-effectiveness of various control strategies in reducing parasite transmission and disease burden. Mathematical modeling is uniquely placed to point to provide a better understanding of this multi-host disease system, identify weak points in the transmission cycle and determine the effectiveness of combinations of interventions to provide rational advice for the planning of control activities.
Goal and specific objectives
We will develop and use mathematical models, calibrated with data from currently ongoing field studies and control efforts, to assess the determinants and key indicators of the transmission dynamicsof O. viverrini and estimate the effectiveness of control interventions, with the following objectives:
- Estimate the contributions of secondary mammalian hosts to the overall transmission of O. viverrini to humans.
- Determine the impact on transmission of varying fishing practices.
- Determine the effectiveness of control interventions in reducing transmission and parasite burden.
Methods
The study will involve:
- Developing deterministic population-based and stochastic individual-based models of the life cycle of O. viverrini including intermediate hosts, humans and reservoir mammalian hosts; and of the effects of control interventions on this system.
- Calibrating these models from available field data, literature reviews and expert opinion.
- Mathematical analyses and numerical simulations, including bifurcation and sensitivity analysis.
- Continuous dialogue with country control programs to ensure model relevance and provide useful feedback from model results.
Expected results and significance
The study will provide for the first time deterministic population-based and stochastic individual-based models of O. viverrini transmission. These will create a basis for comparing likely effects of different control strategies in reducing parasite transmission and burden, assessing the relative contribution ofreservoir hosts, and the impacts of varying fishing practices. This will elucidate the transmission dynamics of O. viverrini, including the role of fish in infecting humans and pets, identify data gaps to inform the design of future experiments and field studies, and will provide a basis for rational planning of control, especially in the context of a new control program in Laos. The project will lay the foundation for modeling the epidemiology and control of related food-borne trematodiasis and consequently of the morbidity associated with these parasitic infections.
