Abstract
Fleas not satisfactorily eliminated by repeated administration of an imidacloprid product to a dog were examined. Flea specimens collected from the dog were identified as the cat flea Ctenocephalides felis. Sensitivity of the flea isolate to imidacloprid and fipronil was evaluated by in vitro knock-down tests in comparison with 3 isolates obtained from other dogs naturally infested by cat fleas. The isolate from the refractory case was found to show low sensitivity to imidacloprid, but was sensitive to fipronil. The fleas on the 4 dogs were then completely eliminated with a spot-on formulation containing fipronil as an active ingredient.
