Roadmap for the development of control strategies for liver fluke

What are we trying to achieve and why? What is the problem we are trying to solve?

Can we develop mechanistic mathematical models to improve on current forecasting systems, which are only applicable to certain regions, and to evaluate novel control strategies?

What are the scientific and technological challenges (knowledge gaps needing to be addressed)?

• Current forecasting systems are empirical and as such cannot be fairly extrapolated to other regions or to future changes because they do not explicitly capture the dependence of the life cycle of F. hepatica on key environmental factors.
• Mechanistic models might be more robust under different and changing conditions, but require detailed knowledge of the life cycle and its dependencies.

What approaches could/should be taken to address the research question?

• Better insights into the effects of environmental conditions on the survival of eggs, metacercaricae and intermediate host snails on pasture in different geographical settings.
• Knowledge of the population dynamics of snail intermediate hosts (IH), and effects of climate and pasture conditions.
• Mathematical and computational model frameworks that are able to address key drivers of fluke epidemiology at a range of scales, for regional forecasting, and within-farm decision support.

What else needs to be done before we can solve this need?

• Field data on prevalence of infection under a wide range of conditions, with which to validate new modelling approaches.
• Tools to more accurately measure metacercariae density on herbage, to validate and refine models at farm level.

Existing knowledge including successes and failures

• Empirical forecasting tools, notably the Ollerenshaw or Mt model, have proven useful in identifying higher risk years and are disseminated to farmers, e.g. in the UK. Environmental correlates of high risk are also well described at regional, farm and individual field scale. There have been some attempts to build mechanistic transmission models but validation has been limited and focused on the same areas.
• Models of within-host processes have been produced, and these would be enhanced by greater understanding of host responses.