TYPE-1 HYPERSENSITIVITY REACTIONS TO MALASSEZIA-PACHYDERMATIS EXTRACTS IN ATOPIC DOGS

Objective-To investigate the potential allergenic role of the yeast Ma lassezia pachydermatis in dogs with clinical diagnosis of atopic derma titis. Animals-5 clinically normal nonatopic dogs, 10 atopic dogs with cytologic evidence of Malassezia dermatitis, and 12 atopic dogs witho ut cytologic evidence of Malassezia dermatitis. Procedure-A crude yeas t extract was produced by disrupting the cell wall of M pachydermatis. The crude extract and 8 of its fractions, which were generated by fra ctionation in a high-performance liquid chromatography column, were in jected along with 46 commercial allergens for intradermal allergy test ing of normal and atopic sample populations. Significant difference be tween atopic populations was evaluated, using a threshold concentratio n of crude yeast extract that failed to induce wheal-and-flare respons es in normal nonatopic dogs. Results-Atopic dogs with cytologic eviden ce of Malassezia dermatitis had significantly greater wheal-and-flare reactions to intradermal injection of crude extract of M pachydermatis than did atopic dogs without cytologic evidence of Malassezia dermati tis. Conclusions-It is concluded that M pachydermatis is capable of pr omoting type-1 hypersensitivity reactions in dogs with an atopic derma titis phenotype. Clinical Relevance-Currently, Malassezia dermatitis i s principally managed by use of antifungal chemotherapy. Because the y east appears to be a contributing allergen in dogs with atopic dermati tis, hyposensitization with M pachydermatis extracts may offer a futur e alternative to extended or repeated episodic administration of antif ungals for extended control of recurrent infections.