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Validation of Current SCOPS Recommendations and Supporting Tools: Effective Worm Control and Delaying the Development of Anthelmintic Resistance - OD0550

Nematode infections are a major cause of ill-thrift, loss of production and death in cattle and sheep, and remain major welfare issues. The epidemiology of nematode species causing disease is directly influenced by climate, anthelmintic usage and patterns of dosing, management and husbandry systems, and these in turn influence the development of natural immunity and the selection pressures that increase the potential for anthelmintic resistance to develop.

There are three main anthelmintic groups: the benzimidazoles (BZ), the levamisoles (LEV) and the macrocyclic lactones (AVER), to which the majority of currently available anthelmintics belong. The routine use of highly effective anthelmintics, and where possible, grazing management, has controlled gastrointestinal worms very successfully in the majority of sheep flocks. Recently, however, the prevalence of anthelmintic resistance in the UK has risen sharply and one or more of the chemical groups are no longer effective against some worm species in an increasing number of flocks.

A number of strategies have been suggested to both control gastrointestinal worms in sheep and limit the development of resistance. The strategies currently employed in most flocks are based on a ‘blue-print’ approach and have the advantage of being relatively cheap and historically effective, for example a key recommendation is the alternation between anthelmintic groups with different modes of action on an annual basis. Whilst this should theoretically reduce the frequency of resistant genes in a population, there have been few studies to monitor the effectiveness of such strategies in the field. Also much of the research on which existing strategies are based is 20-30 years old. In that time there have been significant changes in the size and structure of the sheep industry, the epidemiology of the parasites and the products available. While it is possible that many of the recommendations for worm control are still relevant, they may require modification to take account the current understanding of parasite epidemiology and the development of anthelmintic resistance. A recent initiative in the UK has been a rol out programme of new or revised worm control recommendations produced under the auspices of a steering committee made up of a panel of experts for the Sustainable Control of Parasites in Sheep(SCOPS).

Developing a cost effective, reliable and sustainable strategy, in terms of anthelmintic resistance management for worm control is becoming increasingly complex. On-going consultations between farmers, their veterinarians and advisors will be needed to combine an expert knowledge of worm parasites with a practical and detailed understanding of the individual farm and its sheep flock. The objective of management practices is to minimise the reliance on and use of anthelmintics, by avoiding exposure to parasite burdens that would lead to clinical disease and loss of production. At the same time, management needs to allow the sheep to build up immunity to the parasites if it is to remain on the farm beyond the first grazing season. To achieve these objectives, it is necessary to understand the basic principles of risk assessment for pastures, sheep and systems and be able to relate these to the management and monitoring tools available to the farmer.

Several computer models have been developed to predict both the rate of development of anthelmintic resistance, and the effectiveness of specific control strategies for species of sheep nematodes. Most rely on computer simulations using specific datasets of certain key variables. A computer model that describes population dynamics and the epidemiology of parasitic nematodes of sheep has recently been developed based on expert knowledge and extensive literature review. The model is able to simulate flock dynamics relevant to UK farms and link them to parasite lifecycle models. A user interface has been constructed which facilitates user interaction with the model allowing farm management systems to be defined using a variety of specific input options. As development rates for the parasites are dependant on UK regional climatic data that is included in the model and the region of interest is defined using a map key of the British Isles. A further sector has been built into the model to describe the dynamics of anthelmintic treatments for the main broad-spectrum anthelmintic groups. The model allows the user to carry out simulations and plot the likely dynamics of infection over time using a range of different output options and also to simulate the effect of different treatment strategies and the possible effects such treatments would have on the development of resistance.

Preliminary validation of this model has been completed using 'live' data from a small number of UK farms. To ensure that the model is suitably robust and applicable across a diverse range of UK sheep farms it is necessary to generate further data for model validation. Built into the model validation process will be a roll-out programme for the new SCOPS initiatives linked to a training programme for veterinarians and advisors both in parasite control and use of the model as a tool for evaluating recommended control strategies.
The project aims:

1. To evaluate the practicality and effectiveness of the new guidelines for worm control strategies in sheep, published by SCOPS in 2003.

2. Use the data generated by the samples taken on participating farms to validate the computer model developed under project OD0542 and evaluate it’s use to vets and advisers as a decision support tool for applying SCOPS principles in the field.

3. To use the cohort of commercial farms and data collected for widespread knowledge transfer to farmers and vets to demonstrate the SCOPS recommendations and their application.

4. To update the SCOPS recommendations firstly on the basis of knowledge gained since 2003 and secondly by incorporating the findings of this project.
Project Documents
• FRP - Final Report : OD0550 Final report   (901k)
Time-Scale and Cost
From: 2007

To: 2009

Cost: £603,485
Contractor / Funded Organisations
Central Science Laboratory
Animal Diseases              
Animal Health              
Plants and Animals              
Fields of Study
Animal Health