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Veterinary Medicine International
Volume 2011, Article ID 145312, 4 pages
http://dx.doi.org/10.4061/2011/145312
Research Article

First Report of Anthelmintic Resistance in Gastrointestinal Nematodes of Sheep from Costa Rica

1Laboratorio de Parasitología, Escuela de Medicina Veterinaria, Universidad Nacional, Costa Rica, P.O. Box 304-3000, Heredia, Costa Rica
2Programa de Medicina Poblacional, Escuela de Medicina Veterinaria, Universidad Nacional, Costa Rica, P.O. Box 304-3000, Heredia, Costa Rica
3Servicio Nacional de Salud Animal, Ministerio de Agricultura y Ganadería,, P.O. Box 11965-1000 San José, Costa Rica

Received 19 January 2011; Accepted 24 March 2011

Academic Editor: David W. Horohov

Copyright © 2011 R. Maroto et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

As the prevalence and severity of anthelmintic resistance continue to rise, nematode infections in sheep correspondingly reduce the profitability of the sheep industry. In Costa Rica, sheep production systems are increasing in both number and importance. A field trial study was carried out to detect the level of anthelmintic resistance to albendazole and ivermectin in gastrointestinal nematodes (GIN) of sheep from seven farms in Costa Rica. Resistance was determined using the fecal egg count reduction test (FECRT). Three treatment groups were assessed on each farm: control, albendazole, and ivermectin. Haemonchus spp. (71%), Strongyloides sp. (57%), and Trichostrongylus spp. (43%) presented resistance levels to albendazole, whereas Strongyloides sp. (43%), Haemonchus spp. (29%), and Trichostrongylus spp. (29%) were resistant to ivermectin. Haemonchus spp., Strongyloides sp., and Trichostrongylus spp. were the most resistant GIN to both products. This study suggests that frequency of treatment, exclusive chemical control, and visual estimation of animal weight to calculate dosage may contribute to the high levels of anthelmintic resistance that were observed on the farms analyzed herein.