Clinical forum - Drug resistance in cyathostomins

摘要

Helminths that affect the gastrointestinal tract of horses are an important cause of disease. Of the roundworms (nematodes) that infect horses, those belonging to the Cyathostominae group (also known as cyathostomins or small strongyles) are the mostimportant (Love et al., 1999). This group comprises around 50 different species and so infections can be complex. Usually though, 10-12 common species comprise >90% of the burden with the remainder composed of rarer species. Studies have shown that the same species are common throughout the world.Virtually all grazing horses are exposed to cyathostomins and often animals will be infected all of their lives. Control is compromised by that fact that cyathostomins can develop resistance to the commonly used anthelmintics. Resistance to all three available classes has now been recorded (Molento et al., 2008). As no new equine anthelmintic products appear to be on the horizon, it is important that the efficacy of currently effective drugs be maintained foras long as possible. Strategies to retain anthelmintic efficacy are now being promoted: these are based on the concept that the proportion of worms not exposed to a drug at each treatment is an important factor in the rate at which drug resistance develops. This 'non-exposed' population is termed as being in refugia and control strategies that retain this element in any given population should be utilised. This review provides background information for nematode control programmes that take into account the need to balance anthelmintic treatments to control nematode-associated disease with the requirement to preserve drug efficacy.