Worm control in sheep in the future

Endoparasitic infestations cost the livestock industry many millions of pounds each year through losses in productivity and the costs of control measures. Effective control of these endemic ubiquitous diseases is important, particularly given the expanding world population and the expectation of an increasing demand for ruminant products. Currently, these debilitating ruminant infestations can be controlled prophylactically by using chemotherapy, immunomanipulation and/or management of the grazing environment, but most farmers currently rely upon having effective anthelmintics. Unfortunately, studies on the incidence and prevalence of anthelmintic resistance throughout the world suggest that production systems that are wholly reliant upon intensive chemotherapy/prophylaxis are not sustainable. Current research is examining chemical strategies that will provide good worm control and will also enable the conservation of efficacy of our current and any novel anthelmintics. Maintaining an infra- and supra-population of worms in refugia (i.e., unexposed to anthelmintics) is accepted by most veterinary parasitologists as the best means of maintaining the genes for susceptibility within the parasite population. Maintained susceptibility within a parasite population can be achieved in a variety of ways, all of which utilise a targeted treatment approach to some extent. Whole flock targeted treatment can be optimised using faecal egg count monitoring and individuals can have targeted selective treatments administered on the basis of morbidity markers, such as anaemia, production efficiency assessed by liveweight gain or milk production. There is also a growing interest in bioactive forages, which can have both direct anthelmintic effects and/or indirect anthelmintic effects, where the benefit derives from nutritional effects which boost the host immune responses against nematodes. In the future, arguably the most exciting area is that of immunomanipulation, where current advances in genomics and proteomics offer scope for the development of vaccines and genetic or bio-markers associated with infection or effective immunity. We have been able to identify and select genetically resistant animals for many years by using phenotypic markers for endoparasitism, but it is only recently that the first genetic marker for host resistance has become available. Further research is also needed to identify better phenotypic and genotypic markers for resilience, since in some production systems this may be a more desirable trait than resistance. The implementation of an integrated approach to control to develop sustainable control strategies represents a formidable challenge for the sheep industry. This integrated approach will require well-informed veterinarians; advisors and researchers will need to find the tools to support the practitioners, as well as to find ways of delivering them in an affordable way. Although at present these demands may seem both unobtainable and unaffordable, the development of collaborative multidisciplinary research programmes coupled with advancing high throughput technologies offers the prospect of real progress in this area in future.