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?

More accurate, convenient and affordable diagnostic tests are needed to support surveillance and to enable appropriate intervention at farm level.

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

• Tests are available but all have limitations. Especially important is to determine the time of first infection in autumn in order to drive timely intervention, and tests for anthelmintic resistance, which are currently limited by low sensitivity of faecal egg counts and limited availability of genetic markers. Specific detection of immature fluke infections is needed but currently not available.
• There are some candidate tests that showed promising results in individual laboratories, but these would have to be standardised for widespread use and clear interpretation.
• Requirement of penside/point of care tests for immediate estimate of infection (e.g. for quarantine treatments/choice of treatment of individual animals or groups of animals).

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

• Tracked longitudinal experimental and natural infections with candidate diagnostic indicators of early infection.
• Correlation of tests for level of infection with productivity to determine thresholds for intervention.
• Molecular genetic approaches to find markers of resistance.
• More sensitive and convenient ways of extracting and enumerating eggs in faeces to support quantification of infection and drug efficacy.
• Ring-tests to confirm consistency of results between laboratories as a precursor for widespread use and commercial adoption.

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

• Seeking tests for resistance depends on access to fluke populations of known drug susceptibility.
• Tests for early infection require known timing of infection, hence experimental animal studies.
• Tests intended for surveillance and on-farm decision support must be cheap and convenient enough for easy application.

Existing knowledge including successes and failures

• Promising advances include copro-antigen and copro-DNA tests for early fluke infection, bulk and individual milk immunodiagnostics for fluke-specific antibody levels, and pooled faecal egg count tests to estimate drug efficacy.
• Monitoring tegumental changes in juvenile flukes recovered from slaughtered animals and incubated in triclabendazole can be used to evaluate resistance but are a research tool only.
• As in nematodes, in vitro tests for resistance either by bioassay or using molecular indicators remain held back by limited knowledge of the mechanism and genetic basis of resistance to different drug classes.
• This impedes development of resistance tests that can be reliably used in the field, and be convenient and affordable enough to be taken up by farmers and advisors.