Roadmap for nematode control strategies

Sustainable management of nematode parasites to minimise production loss and welfare implications. Problem is drug resistance so need to simultaneously reduce dependence on conventional anthelmintics and maintain efficacy of current and novel control methods.

Main industry challenge is failure of current drug-based control methods due to anthelmintic resistance (AR). Headline technical /scientific challenges are consequently:
Measurement of AR. Gap: reliable and affordable tests for field and laboratory use to monitor efficacy and allow early reaction.
Preservation of drug efficacy. Gaps: (a) understanding of how refugia can attenuate AR development and providing adequate evidence base and technical tools to implement refugia in practice in different production systems. (b) Lack of proven tools and/or methods to restore efficacy once lost.
Evaluation of alternative parasite management approaches. Gaps: standardised methods to quantify effects of alternative control methods; optimisation of their use to maximise production / economic impacts; integration of multiple methods in different environments.

Itemised list of priority challenges:
(a) Practical tests with high sensitivity and specificity for detection of AR, to enable routine efficacy monitoring.
(b) Robust and user-friendly means to quantify infection thresholds for intervention in groups and/or individual animals across ages, physiological stages and breeds, in different management conditions.
(c) Quantitative knowledge of the factors acting on nematode stages outside the definitive host in different ecosystems and vegetation types and how they contribute to refugia and can be managed to slow resistance and/or reduce overall nematode exposure.
(d) Mechanisms used by different host species and possibly breeds to avoid, control or expel their infection, including immune resistance, innate responses, repellence and resilience.
(e) Changes caused in micro-biota and host environment in case of infection and when consuming different types of vegetation, and how this could be associated with different levels of host susceptibility.
(f) Identify mechanisms of interaction between nematodes and other parasites and microbes, and how they influence integrated parasite control strategies.
(g) How to identify and produce susceptible nematodes to enhance the reversion of resistance of parasites at local and regional levels.
(h) Identify what level of nutrition can achieve sufficiently high resilience and resistance against nematodes to reduce dependence on anthelmintic treatments.
(i) Dose confirmations for ‘minor’ host species such as goats, deer, camelids, rabbits, turkeys, pheasants, etc.
(j) Thresholds of consumption of fresh or preserved nutraceutical/ bioactive plants for significant control of nematodes.
(k) Identify the role of wildlife in the epidemiology of nematodes in livestock.

(a) Validation of pen-side field diagnostic tools to measure levels of infection, drug resistance and individual animals needing treatment.
(b) Define thresholds (economic + parasitological) that support decisions for treatment regimens that minimise unnecessary use of drugs, and slow the development of AR.
(c) Identify the mechanisms of defence of different livestock species and breeds.
(d) Identify the genetic basis of host resistance to support targeted treatment and selective breeding.
(e) Design control strategies with a holistic perspective that involve the most relevant nematodes and co-infections for each region.
(f) Evaluate integrated use of bioactive plants in pasture management.
(g) Different global regions must preserve treatment-naïve parasites for future attempts to achieve reversion to susceptibility.
(h) Perform dose confirmation trials for treatment options in those host animal species considered of minor economic relevance.
(i) Implement worldwide production of Haemonchus contortus vaccine for all the areas where this parasite may cause problems.
(l) Implement clear harmonization guidelines for the evaluation of plant materials used either as nutraceuticals or in the form of medicinal remedies.

Cost benefit analysis of the various treatment options.
Knowledge of stakeholder acceptability.
Generate information on the survival of on-pasture nematode stages in different regions to confirm viability of grazing management strategies.
Develop new vaccines and means for their effective global dissemination.
Develop new therapeutics.
Animal management strategies that minimise disease including using less susceptible breeds of animals and co-grazing strategies.
Guidelines to evaluate nutraceutical materials.

(a) Most studies focus on single species infections but multiple parasite species are the norm.
(b) Nutrition is the source of parasites and also a cornerstone solution for integrated parasite control of livestock, but is rarely considered when evaluating control strategies.
(c) Interactions between plants, gut microbiota and parasites have been neglected.
(d) Missing information on feeding behaviour patterns affecting level of infection, and mechanisms affecting plant selection and appetite.
(d) Lack of harmonization guidelines to test the efficacy of plant medicinal remedies or nutraceuticals.
(f) Available tools to identify animals with high worm burdens, and drug efficacy, depend on time-consuming laboratory methods, or indirect methods with very poor sensitivity and specificity, leaving farmers without a practical on-farm diagnostic alternative.
(g) There is sufficient evidence of efficacy against Haemonchus contortus for copper oxide wire particles and the Barbervax© vaccine (in sheep) and lungworm vaccine (for cattle in endemic areas) to propose them as viable alternative approaches for the control of nematodes that may reduce the use of conventional drugs.
(h) Nematophagus fungi can also be considered a viable alternative control tool but needs more evidence under hot tropical farming conditions were larvae die naturally in short periods of time.