Resistance of population-B equine strongyles to thiabendazole, oxfendazole, and phenothiazine (1981 to 1987).
Critical tests were completed on foals (n = 15) naturally infected with benzimidazole (BZ)-resistant population-B strongyles during the period between 1981 and 1987. Thiabendazole at a dosage of 44 mg/kg was tested in 8 foals, oxfendazole at 10 mg/kg was tested in 4 foals, and phenothiazine at 55 mg/kg, cambendazole at 20 mg/kg, and fenbendazole at 5 mg/kg were tested in 1 foal each. Efficacies of thiabendazole, cambendazole, and fenbendazole against the 5 species of BZ-resistant small strongyles (Cyathostomum catinatum, Cyathostomum coronatum, Cylicocylus nassatus, Cylicostephanus goldi, and Cylicostephanus longibursatus) were partial. Removals in the aggregate averaged 48%, 52%, and 68%, respectively, indicating continued resistance of the 5 species of small strongyles to thiabendazole, cambendazole, and fenbendazole. In contrast, oxfendazole was efficacious, removing an aggregate average of 95% of the 5 BZ-resistant species of small strongyles in the 4 foals. This apparent reversion to susceptibility to oxfendazole may be attributable to paucity of reference data (1 test foal) done in 1976. All 5 species of the BZ-resistant small strongyles had cross resistance to phenothiazine (38% aggregate removal), whereas 9 of the BZ-susceptible species were effectively (99%) removed. This suggests a similar mode of action between phenothiaznie and the BZ compounds.
Department of Veterinary Science, Gluck Equine Research Center, University of Kentucky, Lexington 40546-0099.
J H
JH
Drudge
E T
ET
Lyons
S C
SC
Tolliver
D000818:Animals; D000969:Antinematodal Agents / Q000494:pharmacology / Q000627:therapeutic use; D001562:Benzimidazoles / Q000494:pharmacology / Q000627:therapeutic use*; D002159:Cambendazole / Q000494:pharmacology / Q000627:therapeutic use; D004351:Drug Resistance; D005243:Feces / Q000469:parasitology; D005260:Female; D006736:Horses; D007814:Larva / Q000187:drug effects / Q000302:isolation & purification; D008297:Male; D010270:Parasite Egg Count / Q000662:veterinary; D010640:Phenothiazines / Q000494:pharmacology / Q000627:therapeutic use; D013319:Strongyle Infections, Equine / Q000188:drug therapy* / Q000469:parasitology; D013320:Strongyloidea / Q000187:drug effects* / Q000302:isolation & purification; D013827:Thiabendazole / Q000494:pharmacology / Q000627:therapeutic use
D000969:Antinematodal Agents; D001562:Benzimidazoles; D010640:Phenothiazines; D002159:Cambendazole; C031637:phenothiazine; D013827:Thiabendazole; C011030:oxfendazole