Cross-sectionele studie naar de soortensamenstelling van cyathostominae larven en de soort specifieke gevoeligheid voor ivermectine
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Cyathostomins are one of the most feared pathogenic helminths of horses. The prevalence is high and an increasing resistance of cyathostomins against anthelmintics is seen worldwide. In this study, the species composition of cyathostomins larvae and the species-specific sensitivity to ivermectin is being researched on four horse farms in The Netherlands. In this substudy fecal samples have been taken from three populations that vary in deworming intensity. The populations are horses from Castricum (CAS), that haven’t had anthelmintics for at least four years, Shetlanders from the Utrecht University (UU), that have been treated regularly and horses from the Oostvaardersplassen (OPV), that have never been in contact with anthelmintics in their lives. With larvae bred from the fecal samples a reiterative Larval Migration Inhibition Assay (rLMIA) has been performed. The larvae migrated at two concentrations ivermectin through two sieves. A therapeutic concentration of 0,24 µg/ml ivermectin and a maximum quantity of soluble ivermectin of 30µg/ml. In the rLMIA larvae with a reduced sensitivity to ivermectin were selected. Larvae that migrated through the sieve, showed reduced sensitivity to ivermectin. Subsequently Reverse Line Blot hybridization (RLB) was used to determine the species composition. The populations UU and OVP on both concentrations ivermectin showed an increase in migration percentage in the rLMIA. Within the CAS population an increase in migration percentage was seen only with the concentration of 0,24 µg/ml ivermectin. The CAS and UU population had their species composition determined. Also their sensitivity to ivermectin per species has been analyzed. The starting material of the CAS population predominantly held the species Cyathostomum catinatum (36%), Cylicostephanus goldi (34%) and Cylicostephanus longibursatus (25%). C. catinatum and C. longibursatus showed a decreased sensitivity to ivermectin. This intensitive can be acquired or innate. The migration percentage for C.catinatum increases with the second migration. The migration percentage for C. longibursatis increases less and no increase is seen with C. goldi. So it can be stated that the species C. catinatum is more heterogenic and this is probably an acquired intensitivity. In the population UU, C. nassatus is the most common species (71%) and it showed a clear sensitivity to ivermectin. The study has shown, using rLMIA, the possibility to select ivermectin intensitive cyathostomins larvae within one species.