Elimination of an Infestation of Rat Fur Mites (Radfordia ensifera) from a Colony of Long Evans Rats, Using the Micro-dot Technique for Topical Administration of 1% Ivermectin

Micro-dot delivery of 1% ivermectin was used in an effort to eliminate an infestation of rat fur mites (Radfordia ensifera) from a conventionally housed colony of Long Evans rats. The colony was used for breeding as well as for behavioral testing. A micropipette was used to apply a 1% solution of ivermectin (2 mg/kg of body weight) to the skin on the dorsal aspect of the shoulder. Three treatments were applied at approximately 2-week intervals. All rats in the colony were treated. However, to avoid toxicity to neonates, nursing females and their pups (control group) received mineral oil in lieu of ivermectin until after weaning, at which time they also were treated with ivermectin. During the treatment phase, skin scrapings were used to detect mites. Control rats remained positive for fur mites when treated with mineral oil. After 3 applications of ivermectin, all rats were found to be free of mites. During the posttreatment phase, skin scrapings, dorsal tape tests, and a washing method were performed on euthanatized rats to detect mites. Rats tested up to 129 days (18 weeks) after ivermectin treatment were still free of mites. In a breeding colony composed of rats of various sizes and ages, micropipette delivery of ivermectin allowed for accurate dosing to eliminate fur mites, while preventing inadvertent toxicosis. We did not detect obvious adverse effects on the breeding program or on the behavioral studies in which these rats were subsequently used, nor did we detect morbidity or mortality associated with ivermectin administration.