title: Survey for drug-resistant gastrointestinal nematodes in 13 commercial sheep flocks.
abstract: The prevalence of drug-resistant ovine parasites in the United States has not been widely reported. Thirteen flocks, typical of commercial sheep production units, were selected for survey. Four anthelmintics (fenbendazole, ivermectin, pyrantel pamoate, and levamisole) were tested for their ability to reduce herd mean pretreatment fecal egg count. If a properly dosed and administered drug failed to reduce herd mean pretreatment fecal egg count by 80%, it was considered ineffective in that flock, and the presence of parasites resistant to that drug was inferred. Fenbendazole administration changed pretreatment fecal egg counts by +9% to -100%. On the basis of the aforementioned definition, drug resistance existed in 6 of 13 flocks. Posttreatment larval culture indicated that Haemonchus contortus survived administration of fenbendazole. Levamisole, pyrantel pamoate, and ivermectin reduced pretreatment fecal egg count by -83% to -100%; resistance to these products was not evident in the flocks surveyed.
authors.affiliation: Department of Food Animal and Equine Medicine, College of Veterinary Medicine, North Carolina State University, Raleigh 27606.
authors.forename: C
authors.initials: C
authors.lastname: Uhlinger
authors.forename: S
authors.initials: S
authors.lastname: Fleming
authors.forename: D
authors.initials: D
authors.lastname: Moncol
mesh_terms: D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology* / Q000627:therapeutic use; D004351:Drug Resistance; D005243:Feces / Q000469:parasitology; D005260:Female; D005273:Fenbendazole / Q000494:pharmacology / Q000627:therapeutic use; D007411:Intestinal Diseases, Parasitic / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary*; D007559:Ivermectin / Q000494:pharmacology / Q000627:therapeutic use; D007978:Levamisole / Q000494:pharmacology / Q000627:therapeutic use; D009348:Nematoda / Q000187:drug effects*; D009349:Nematode Infections / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary*; D010270:Parasite Egg Count / Q000662:veterinary; D011716:Pyrantel Pamoate / Q000494:pharmacology / Q000627:therapeutic use; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy / Q000469:parasitology*
chemical_list: D000871:Anthelmintics; D007978:Levamisole; D005273:Fenbendazole; D007559:Ivermectin; D011716:Pyrantel Pamoate