AN ORAL IVERMECTIN REGIMEN THAT ERADICATES PINWORMS (SYPHACIA SPP) INLABORATORY RATS AND MICE

Pinworm infection, a common problem in laboratory rodent colonies, is difficult to control because anthelmintics like ivermectin eliminate a dult worms but have no effect on ova, which can survive ex vivo for pr olonged periods, On the premise that repeated treatments with ivermect in would keep rodents parasite-free until all ova matured into ivermec tin-susceptible worms in vivo or died in vivo or ex vivo, 80 rats and 25 mice heavily infected with pinworms (Syphacia obvelata and S. muris ) were randomized to receive two to five courses of ivermectin 3 days apart or no treatment, During each treatment, ivermectin was given for 4 days in the drinking water; based on water consumption, the mean iv ermectin dose was 2.9 and 4.0 mg/kg of body weight per day in rats and mice respectively, Ova production was monitored by weekly cellophane tape tests; 29 to 32 weeks after treatment ended, all rodents were eut hanized, and their evacuated large intestinal contents were examined f or adult pinworms and ova, Despite intermittently negative cellophane tape test results in untreated rodents (10 rats and 5 mice), all were infected with parasites at the end of the follow-up period, These find ings underscore the limitations of the tape test for diagnosis of pinw orm infection, After two courses of ivermectin, 1 of 10 rats and four of five mice were infected, whereas after three courses only 1 of 40 r ats and one of five mice had parasites, In contrast, none of the 20 ra ts or 10 mice given either four or five courses of ivermectin had para sites at 30 to 32 weeks of follow up evaluation, This simple and well- tolerated ivermectin regimen may help to treat and control pinworm inf ection in laboratory rodent colonies.