A cost comparison of faecal egg count-directed anthelmintic delivery versus interval programme treatments in horses

The frequent use of anthelmintics in horses has contributed to the development of widespread anthelmintic resistance in cyathostomins (Matthews 2008, 2011), a group of parasitic nematodes comprising around 50 species. Cyathostomins are highly prevalent in grazing equids globally and have great pathogenic potential due to their capacity to cause life-threatening colitis when present in high numbers (Love and others 1999). Most cyathostomin infections are well tolerated; however, mass emergence of encysted larvae from the large intestinal wall can result in larval cyathostominosis, characterised by diarrhoea, rapid weight loss and oedema, which can be fatal in up to 50 per cent of cases (Love and others 1999). Currently, three classes of broad spectrum anthelmintics are licensed for use against adult cyathostomin worms in the UK; fenbendazole (FBZ; a benzimidazole, BZ), pyrantel embonate (PYR; a tetrahydropyrimidine, THP) and the macrocyclic lactones (ML), ivermectin (IVM) and moxidectin (MOX). BZ resistance is ubiquitous, (Kaplan and others 2004, Osterman Lind and others 2007, Traversa and others 2012, Stratford and others 2013a) and reduced sensitivity of cyathostomins to PYR is common in certain geographic areas (Kaplan and others 2004, Comer and others 2006, Osterman Lind and others, 2007, Traversa and others 2009). Single cyathostomin populations have been identified that exhibit both FBZ and PYR resistance (Kaplan 2004, Traversa and others, 2009). A reduction in the standard strongyle egg reappearance period following ML administration has been reported, and is generally accepted as an early indicator of resistance …