Immunopathology of Naturally Occurring Otodectic Otoacariasis in the Domestic Cat

Abstract

SUMMARY The consequences of naturally occurring feline otoacariasis due to Otodectes cynotis were evaluated, using morphologic, clinical laboratory, histopathologic, and immunologic criteria. The chief histopathologic findings in the external auditory canal of affected cats consisted of hypertrophy of squamous epithelium, acanthosis, hyperplasia of sebum-producing glands, hyperemia, edema, and infiltration of the dermis with chronic inflammatory cells. The latter included mast cells, lymphocytes, and plasma cells as the principal elements. These findings were related to an understanding of subsequently demonstrated immunologic reactions. Using aqueous whole-mite extracts as antigen for intradermal injections in cats with otoacariasis, evidence of immediate and Arthus-type hypersensitivity, but not delayed hypersensitivity, was obtained. The occurrence of Arthus-type hypersensitivity was found to be associated with the presence of precipitins, as detected by agar-gel immunodiffusion. In clinically normal cats, evidence of immediate (and to a lesser degree Arthus-type) hypersensitivity was frequently obtained, indicating prior experience with O cynotis . Barrier-reared pathogen-free cats were nonreactive to intradermal injections of the antigen and did not have precipitin antibodies.