Type-I hypersensitivity to Malassezia pachydermatis extracts in healthy dogs and dogs with Malassezia otitis externa

The purpose of the study reported here was to test the hypotheses that clinically healthy dogs will not manifest immediate hypersensitivity responses to intradermal injection of Malassezia pachydermatis extracts but that affected dogs with Malassezia otitis will manifest such hypersensitivity. We desired to identify approximate molecular mass of any allergenic components of the yeast by use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The protein profile of Malassezia pachydermatis extracts showed between 16 and 110 kDa. Especially, the intensity was strongest between 25 and 80 kDa. Mean wheal diameters in the affected groups of 20, 2, 0.2, and 0.02 μg/ml were 13.36 ± 0.67, 5.33 ± 0.67, 5.47 ± 0.82, and 5.07 ± 0.64, respectively. Mean wheal thickness in the affected groups of 20, 2, 0.2, and 0.02 μg/ml was 6.44 ± 0.40, 3.86 ± 0.35, 2.64 ± 0.36, and 2.60 ± 0.44, respectively. The difference of wheal diameters and thickness between healthy and affected groups was significant (p < 0.05). In conclusion, the observations confirm that Malassezia pachydermatis-derived antigens may induce an immediate wheal response when intradermal injected in dogs. It seems reasonable to suggest that hypersensitivity to yeast may contribute to the development of clinical signs in dogs with immediate skin test reactivity, especially in dogs with Malassezia otitis externa.