Malassezia spp Testing

Malassezia pachydermatis is part of the normal flora of canine skin but can be an opportunistic pathogen. Malassezia spp hypersensitivity is a complicating factor in canine atopic dermatitis. Both immediate-type and delayed-type hypersensitivity reactions have been documented.

Intradermal skin testing (IDT) and serum IgE testing attempt to identify potentially applicable immediate-type hypersensitivity reactions in clinically affected dogs and may be used to formulate allergen-specific immunotherapy. However, IDT is typically available only through dermatologists, and Malassezia spp-specific serum IgE tests may not be included on typical panels marketed to general practitioners.

In this study, IDT and serum anti-IgE enzyme-linked immunosorbent assay (ELISA) testing were compared in 84 atopic dogs. There was considerable agreement between IDT reactivity and anti-Malassezia spp IgE ELISA. ELISA sensitivity and specificity were 77% and 89%, respectively, relative to IDT results.

The study did not evaluate the correlation of the IDT or ELISA tests with clinical signs or cytology; these 3 elements of patient evaluation may be used in combination for thorough patient assessment and treatment planning. *Allergen specific IgE assays were performed gratis by Heska Corporation.

From a general practitioner’s standpoint, Malassezia spp availability on a serum allergen profile may be quite helpful, as IDT is typically not performed because of cost constraints. When an owner does not elect referral, serum allergen testing can still be appropriate for immunotherapy formulation.

It would be interesting to see whether or how frequently positive Malassezia spp-specific IgE is detected in serum of dogs with suspected Malassezia spp hypersensitivity, thereby validating clinical implications of this diagnostic. As with other atopic dermatitis triggers, though, it is important to remember that neither intradermal nor serum-based allergen testing should be used in diagnosing atopy. Appropriate use of these tests in practice (ie, after a clinical diagnosis has been made to support and help guide immunotherapy formulation) will allow for validating the use of measuring serum Malassezia spp-specific IgE in the clinically atopic patient.—Alison Diesel, DVM, DACVD, Texas A&M University