title: Resistance of gastrointestinal nematodes to the most commonly used anthelmintics in sheep, cattle and horses in Spain.
abstract: The objective of this study was to evaluate the status of anthelmintic resistance (AR) in ruminants and horses in Spain. The efficacy of commonly used macrocyclic lactones (MLs) - ivermectin (IVM) and moxidectin (MOX) - was measured in sheep, cattle and horses. In addition, albendazole (ABZ) and levamisole (LEV) were evaluated in sheep and oxibendazole (OXI) and pyrantel (PYR) in horses. Efficacy was evaluated based on the difference between the arithmetic mean pre- and post-treatment faecal egg count (in cattle and horses), or compared to an untreated control group (in sheep). AR was present when the percentage reduction in egg count was <95% and the lower 95% confidence interval (CI) was <90%; if only one of these two criteria was met, the finding was recorded as suspected AR (SAR). In horses, AR-PYR and OXI was considered when the percentage reduction in egg count was ≤ 90% and the lower 95% CI was ≤ 80%. For each animal species, at least 10 study sites were selected. AR to at least one of the drugs was detected in all 10 sheep flocks; the main parasite identified after treatment was Teladorsagia circumcincta. Moreover, in 5 flocks multidrug resistance was identified, on 4 farms to drugs from different families, on one farm to both MOX and IVM and on another farm to all drugs tested. In cattle, the efficacy of both MOX and IVM was 100% on 4 and 3 farms, respectively, and therefore 60% of these farms were considered to have AR or SAR to both MLs. The most frequent parasite identified after treatment was Trichostrongylus spp., although Ostertagia ostertagi was also identified after treatment on one farm. In contrast to ruminants, the 4 drugs evaluated in horses were highly efficacious against strongyles, with efficacies for the MLs and OXI between 95 and 100% and between 94 and 100% for PYR, although 3 herds were SAR against PYR. In conclusion, AR to at least one of the commonly used drugs was identified on all sheep flocks investigated in the northwest of Spain. The occurrence of AR to MLs in cattle was higher than expected but consistent with what was observed in sheep. In horses, all currently used drugs were confirmed as effective against strongyles.
authors.affiliation: Instituto de Ganadería de Montaña (CSIC-ULE), Finca de Marzanas, 24346 Grulleros, León, Spain. Electronic address: mmarva@unileon.es.
authors.forename: M
authors.initials: M
authors.lastname: Martínez-Valladares
authors.affiliation: Zoetis, Mercuriusstraat 20, 1930 Zaventem, Belgium.
authors.forename: T
authors.initials: T
authors.lastname: Geurden
authors.affiliation: Zoetis, Mercuriusstraat 20, 1930 Zaventem, Belgium.
authors.forename: D J
authors.initials: DJ
authors.lastname: Bartram
authors.affiliation: Departamento de Sanidad Animal, Facultad de Veterinaria, Universidad de León, Campus de Vegazana, 24071 León, Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: Martínez-Pérez
authors.affiliation: Departamento de Sanidad Animal, Facultad de Veterinaria, Universidad de León, Campus de Vegazana, 24071 León, Spain.
authors.forename: D
authors.initials: D
authors.lastname: Robles-Pérez
authors.affiliation: Departamento de Sanidad Animal, Facultad de Veterinaria, Universidad Complutense de Madrid, 28040 Madrid, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Bohórquez
authors.affiliation: Departamento de Sanidad Animal, Facultad de Veterinaria, Universidad Complutense de Madrid, 28040 Madrid, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Florez
authors.affiliation: Departamento de Sanidad Animal, Facultad de Veterinaria, Universidad Complutense de Madrid, 28040 Madrid, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Meana
authors.affiliation: Instituto de Ganadería de Montaña (CSIC-ULE), Finca de Marzanas, 24346 Grulleros, León, Spain; Departamento de Sanidad Animal, Facultad de Veterinaria, Universidad de León, Campus de Vegazana, 24071 León, Spain.
authors.forename: F A
authors.initials: FA
authors.lastname: Rojo-Vázquez
mesh_terms: D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology*; D002417:Cattle; D002418:Cattle Diseases / Q000469:parasitology*; D004351:Drug Resistance; D006734:Horse Diseases / Q000453:epidemiology / Q000469:parasitology*; D006736:Horses; D009348:Nematoda / Q000187:drug effects*; D009349:Nematode Infections / Q000453:epidemiology / Q000469:parasitology / Q000662:veterinary*; D012756:Sheep; D012757:Sheep Diseases / Q000453:epidemiology / Q000469:parasitology*; D013030:Spain / Q000453:epidemiology
chemical_list: D000871:Anthelmintics
keywords: Anthelmintic resistance; Cattle; Drugs; Horses; Nematodes; Sheep