Practical and effective eradication of pinworms (Syphacia muris) in rats by use of fenbendazole

Oxyurid parasites are common contaminants of laboratory rodents, and despite many described treatments, no method has assumed preeminence. Limitations in drug efficacy and the general inability to control for exposure to infective eggs are the primary contributors to treatment failure. In addition, some effective drugs must be eliminated from consideration because of narrow safety margins, other toxic aspects, or concerns related to particular uses of the experimental animals. As an alternative to currently described treatments or surgical derivation, we conducted an efficacy study against Syphacia muris in rats with a new fenbendazole-based protocol. Fenbendazole is a highly efficacious broad-spectrum anthelmintic with adulticidal, larvicidal, and ovicidal actions. Its pharmacokinetic behavior, ovicidal activity, and exceptionally wide safety margin in rats and mice make it an attractive choice for pinworm treatment. We used a 150-ppm medicated feed formulation to reach a targeted dose of 8.0 to 12.0 mg/kg/day in three separate studies designed to assess drug intake and efficacy under different housing conditions and in breeding and nonbreeding populations of ACI rats. In all cases, drug was given on alternating weeks, and nonbreeding populations were medicated for a cumulative period of 14 days. The same schedule was used for breeding populations, but the treatment was repeated after a 2-week rest period to ensure sufficient exposure for newly weaned animals. The results of our study indicate that our described treatment, in combination with environmental control measures against pinworm eggs, is capable of eliminating S. muris.