Anthelmintic resistance in nematodes of horses

Abstract

-Suppressive anthelmintic treatment strategies originally designed to control Strongylus vulgaris in horses were extremely successful in reducing morbidity and mortality from parasitic disease. Unfortunately, this strategy has inadvertently resulted in the selection of drug-resistant cyathostomes (Cyathostominea), which are now considered the principal parasitic pathogens of horses. Resistance in the cyathostomes to benzimidazole drugs is highly prevalent throughout the world, and resistance to pyrantel appears to be increasingly common. However, there are still no reports of ivermectin resistance in nematode parasites of horses despite 20 years of use. It is unknown why resistance to ivermectin has not yet emerged, but considering that ivermectin is the single most commonly used anthelmintic in horses most parasitologists agree that resistance is inevitable. The fecal egg count reduction test is considered the gold standard for clinical diagnosis of anthelmintic resistance in horses, but diagnosis is complicated by lack of an accepted standard for the performance of this test or for the analysis and interpretation of data. Presently there is very little data available on the molecular mechanisms of anthelmintic resistance in cyathostomes; β-tubulin gene is the only anthelmintic-resistance associated gene that has been cloned. The increasingly high prevalence of anthelmintic-resistant cyathostomes must be taken into account when designing worm control programs for horses. Strategies to decelerate further selection for drug resistance thereby extending the lifetime of currently effective anthelmintics should be implemented whenever possible. Considering the nature of the equine industry in which horses often graze shared pastures with horses from diverse locations, transmission and widespread dispersal of resistant parasites is virtually assured. A proactive approach to this problem centered on understanding the molecular basis of anthelmintic resistance in cyathostomes is required if we are to expect chemical control of nematodes in horses to remain a viable element of parasite control in the future.cyathostome / anthelmintic / resistance / nematode / horse Résumé -La résistance aux anthelmintiques chez les nématodes des chevaux. Les stratégies des traitements anthelmintiques mises en place à l'origine pour contrôler Strongylus vulgaris chez les chevaux ont été extrêmement efficaces pour réduire la morbidité et la mortalité dues aux maladies 491

Recent developments in research into the Cyathostominae and Anoplocephala perfoliata

“…Resistance to the widely used BZ class of drugs is the most prevalent and has been documented in numerous countries throughout the world [33]. The issue of cyathostomin anthelmintic resistance has been discussed extensively by Kaplan [23] and will not be addressed in detail here, however we will highlight the current situation with respect to the molecular analysis of cyathostomin anthelmintic resistance.…”

“…Currently, these parasites demonstrate resistance to two of the three classes of anthelmintic, the benzimidazoles (BZ, fenbendazole, oxfendazole) and the tetrahydropyrimidines (pyrantel) [23]. Resistance to the widely used BZ class of drugs is the most prevalent and has been documented in numerous countries throughout the world [33].…”

Immunoprotection in goats against Haemonchus contortus after immunization with cysteine protease enriched protein fractions

“…The control of H. contortus is largely based on pasture management and the use of anthelmintics. Clean pastures are not, however, readily available under intensive grazing conditions and there is an increasing occurrence of parasites resistant to anthelmintics [4,11,15,28,30,31]. Therefore, increasing attention has been given to the development of alternative control methods such as the use of vaccines.…”

Poor efficacy of the most commonly used anthelmintics in sport horse nematodes in Morocco in relation to resistance

“…order to control infection; it resulted in an increase of small strongyles which were considered as much less pathogenic than large strongyles (Kaplan, 2002). The first reports of thiabendazole resistance in the cyathostomes (= small strongyles) were recorded by Drudge & Lyons, 1965; later, it has been extensively reported in many countries (Lyons et al, 1999).…”

“…The first reports of thiabendazole resistance in the cyathostomes (= small strongyles) were recorded by Drudge & Lyons, 1965; later, it has been extensively reported in many countries (Lyons et al, 1999). Resistance to pyrantel was reported only in recent years although it has been used since the 1970's, and mostly in places were daily feeding with pyrantel is practised (Kaplan, 2002). Resistance to organophosphate is not documented in horse nematodes.…”