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?

• Sustainable control of liver fluke minimising production losses while delaying the development of resistance to therapeutics.
• The major problem species is Fasciola hepatica. Other liver flukes, especially Fasciola gigantica and Dicrocoelium dendriticum cause problems in some regions. Trematodes in other organs, notably rumen fluke Calicophoron spp. and Paramphistomum spp., are also economically important. This summary focuses on F. hepatica.

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

• Parasites can be controlled with anthelmintics but their frequent use results in the development of resistance.
• The parasite modulates host responses preventing the development of protective immune responses.
• The cost of control methods must be economically viable.
• Infection and production loss persist on many farms in spite of control measures and more efficient use of supportive control approaches such as grazing management is needed but difficult to achieve in practice, especially as epidemiological patterns are altered by climate and management change.
• Fasciola hepatica is zoonotic and causes significant human disease in some localities.

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

• The validation of treatment regimens that minimise the development of anthelmintic resistance.
• The development of alternative control methods such as vaccination, pasture/grazing management.

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

• Cost benefit analysis of the various treatment options.
• Knowledge of stakeholder acceptability.
• Development of vaccines.
• Development of new therapeutics.
• Development of pasture management strategies that minimise disease, including appreciation of the impacts of climate and management change on disease risk.
• Knowledge of the basis and extent of variation in susceptibility between host species and breeds.

Existing knowledge including successes and failures

• Basic life cycle and epidemiology is worked out but important details missing, e.g. on intermediate host range and dynamics, immune responses, genetics of resistance, and alternative control methods.
• Native antigen vaccines have shown promising efficacy in trials but recombinant vaccines have not yet been shown to induce protective responses.