Helminth parasitism is globally considered the most important form of transmissible disease in sheep and goats. Mortalities, ill thrift and the cost of treatments impose a massive annual burden on livestock owners. Despite the availability of highly effective anthelmintic compounds initially resistance in nematodes compromises their effectiveness. The alternative approaches that potentially reduce the reliance on anthelmintics have found limited adoption. Sustainable worm control strategies based largely on ensuring that a source of worms not exposed to anthelmintics (in refugia) remains, so that resistant worms do not become a dominant part of the total population. This may require withholding treatments from a proportion of animals when the whole group would normally be treated. The “targeted selective treatment” approach involves using anthelmintics on an individual animal basis according to indications of parasitic effects, regardless of parasite burdens. For Haemonchus contortus, the FAMACHA system, based on the easily visualized index of anaemia, has proved effective provided that labour is available for frequent inspections. Continuing investigations are necessary to indicate the most appropriate indices for different situations, so that the refugia effect is maximized for the least risk of disease and production loss. Of prime importance, targeted selective treatment strategies must be practical to implement if they are to achieve widespread adoption.
Anthelmintic resistance, Refugia, Parasite, Small ruminant
