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.
Highlights
Costa Rica is a tropical country located in southern Central America
The objective of the present study was to assess the level of gastrointestinal nematode (GIN) anthelmintic resistance in sheep from Costa Rica
Nematode anthelmintic resistance to albendazole and ivermectin was found in 86% (6/7) and 71% (5/7) of the seven sheep flocks, respectively (Tables 1 and 2)
Summary
Costa Rica is a tropical country located in southern Central America. The country is divided into seven provinces and has two defined periods of rainfall: dry (December–April) and rainy (May–November). The total population of sheep in Costa Rica is approximately 7000 head and is distributed mainly throughout Guanacaste, Puntarenas, and Alajuela provinces [2]. The number of sheep and flocks has risen because of an increase in the consumption of lamb meat. A 56% increase in the production of lamb meat in the local abattoir was reported in 2009 [2]. The presence of gastrointestinal parasite in sheep has been reported in Costa Rica, and Haemonchus contortus has been the most important species [2]. Because of an observed loss of efficacy of some products in parasite control, sheep farmers and veterinarians have suspected development of anthelmintic resistance (Montero, 2004; personal communication). The objective of the present study was to assess the level of gastrointestinal nematode (GIN) anthelmintic resistance in sheep from Costa Rica
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