Nocardia asteroides recovery from a dog with steroid- and antibiotic-unresponsive idiopathic polyarthritis.

This report describes a fatal case of idiopathic polyarthritis in a dog that was partially responsive to vigorous immunosuppressive treatment. Synovial fluids were cultured for L-forms at the following stages of disease: (i) acute arthritic relapse, (ii) incomplete remission, and (iii) death. Nocardia asteroides UCD 1-581 was recovered from the L-form broth culture of the specimen taken during acute relapse, 5 weeks after inoculation, but not at any other stage of disease. Numerous conventional microbiological cultures were unproductive during all phases. Changes occurring in L-form plates included the formation of large irregular mineral deposits and many transferable bodies resembling pseudocolonies. Microscopic examination revealed the presence of many intracellular golden-brown granules and acid-fast bodies in macrophages of the lung and bronchial lymph node tissues. The granules are believed to be the variants embedded in calcium deposits similar to those which developed in the L-form cultures in vitro. Fluorescence of these acid-fast bodies with antibody specific for superoxide dismutase of N. asteroides GUH-2 and labeled anti-immunoglobulin G established their relationship to the isolate. The unrelenting course of disease and the persistence of N. asteroides as an L-form in this animal despite vigorous immunosuppression suggest that this organism plays a direct role in the etiology of this disease.