Sustainable Control Of Parasitic Worms In UK Livestock

Published on 23 July 2009 in Sustainability and Communities , Food, health and wellbeing

Parasitic gut worms cost the UK livestock industry several millions of pounds in lost production each year

Introduction

Endemic parasitic diseases such as those caused by roundworms and sheep scab cost the UK livestock industry many millions of pounds per annum due to both losses in productivity and the costs of control, and as such are a major disease component affecting sustainability. Currently, antiparasitic drugs (anthelmintics) form the cornerstone of our control strategies and, with the introduction of novel drugs, are expected to do so for the foreseeable future. However, the intensive use of anthelmintics is now known to be an unsustainable approach due to the development of anthelmintic resistance; these resistant worms now pose a global threat to ruminant livestock farming. It is clear that we require a better understanding of how resistance develops, its genetic basis and associated mechanisms in order to develop best practice advice that will provide effective sustainable roundworm control strategies for our farmers.

Key Points

Moredun Research Institute has unique facilities and the range of research expertise to enable it to tackle the issue of anthelmintic resistance at all levels covering the mechanisms of resistance, its diagnosis using either phenotypic and or genotypic tests and fundamental and applied studies on its development and management.
Researchers at Moredun have isolated, purified and maintained resistant isolates that have been used in its research programme. This research has demonstrated the widespread prevalence of resistance against our three current anthelmintic families and has highlighted the importance of drug transport and metabolism mechanisms in resistance against ivermectin; a member of arguably our most valuable drug family that is used to control both internal and external parasites (endectocide).
These studies have also confirmed the importance of maintaining the size of the worm population unexposed to anthelmintic (in refugia) in order to delay the rate of development of resistance. Reducing anthelmintic usage through effective targeting of treatments has been confirmed as one of the best ways to maintain the population in refugia and thus prolong drug efficacy.
This research is not only important for the conservation of our current drug families but is also vital for the new drug families that are expected to come on the market in the future since it provides best practice advice on the use of anthelmintics.

Research Undertaken

Applied research

Field studies at Moredun have examined the impact of different treatment strategies on the development of ivermectin resistance and in particular have studied the value of moving away from treating the whole flock to treating individuals (targeted selective treatments TST). These studies have used a decision support system developed at Moredun that uses liveweight gain to calculate efficiency of production with only those animals that are not performing efficiently being treated.

Using the TST approach reduced anthelmintic usage by approximately 50% with no deleterious effects on productivity in comparison to a group where all animals were treated monthly. In the 3 years to date, the TST approach has not only maintained anthelmintic efficacy but nearly all of the TST animals that required treatment had a positive response to treatment. In the group where lambs were treated every month resistance against ivermectin became evident with a decline in mean efficacy of 18%. These studies clearly demonstrate the benefits of optimising drug treatments using a TST approach.

Moredun has developed a decision support system using liveweight gain to calculate effciency of production

Fundamental research

Samples of parasite material from the isolates in culture and the field studies are being used in our studies on the mechanisms of resistance and its molecular/genetic basis. The main aim is to identifying novel markers of resistance for Teladorsagia that can be used both diagnostically and to develop effective resistance management strategies. Research on the underlying mechanisms has been aided by the development of two lines of resistant Haemonchus where it has been possible to introduce resistance genes into a susceptible isolate using a backcrossing approach. In vitro and in vivo studies on ivermectin resistance have confirmed the important role played by ABC transporter mechanisms such as the P-glycoproteins in ivermectin resistance and thus identified these as a potential target for novel therapeutics.

Policy Implications

Controlling parasite diseases is vital for the health, welfare and economic sustainability of the UK sheep industry

The increasing world population and expected rising demand for livestock products has focussed attention on the need for food security which can be affected by disease issues. Given the importance of agriculture to Scotland’s economy as a whole, and the need to maintain rural communities, effective control of endemic parasitic diseases is an important issue.

Although there is an expectation of new anthelmintics becoming available in the next few years, it is vital that these are not only used in a sustainable way but also with the aim of maintaining our existing anthelmintics. This is particularly the case for endectocidal chemicals in the macrocyclic lactone family such as ivermectin, doramectin and moxidectin, which are crucial in the fight against those parasitoses that threaten the health, welfare and economic sustainability of the UK sheep industry.

Author

Dr Frank Jackson frank.jackson@moredun.ac.uk

Topics

Sustainability and Communities , Food, health and wellbeing