Skin irritation testing in rabbits complicated by dermal mucormycosis

Two insecticide formulations were evaluated for skin irritation using albino rabbits (Stauffland-White strain). While the active ingredient alone produced only mild skin irritation, corn grit formulation produced severe skin irritation. Corn grit from three sources (A, B, and C) was similarly evaluated for skin irritation and at 24 hr, all samples produced erythema and edema of both the abraded and nonabraded test sites. Eschar was observed in 72 hr in about half of the rabbits and persisted through termination on the 7th day. Histologic examination of skin specimens revealed that all three corn grit samples produced epidermatitis. In addition, rabbits exposed to corn grit from two sources (A and B), developed moderate focal to severe diffuse suppurative necrotizing folliculitis and dermatitis. Large tubular branching nonseptate hyphae compatible with the Mucorales species were seen in hair follicle micropustules of rabbits treated with corn grit from sources A and B. Mycologic culture techniques applied to corn grit from each source revealed a potential pathogen in the genus Rhizopus isolated from samples from sources A and C but not B. The skin irritation test involved application of test material covered with gauze to both abraded and nonabraded skin. Rubber damming was placed over the gauze and secured with tape. After 24-hr exposure all bandaging and visible test material were removed. Skin irritation was evaluated immediately after removal and then periodically until termination at 7 days.