Granulomatous pneumonia in the opossum (Didelphis virginiana) associated with an intracellular fungal agent

Background and Purpose: Two of nine female opossums (Didelphis virginiana) in a closed breeding colony were submitted for necropsy due to a history of poor reproductive performance in the absence of overt clinical disease. On histologic examination, marked granulomatous to pyogranulomatous pneumonia was identified in these animals. Methods: Lung sections were stained with periodic acid-Schiff and Gomori's methenamine silver nitrate. Results: Pulmonary lesions were characterized by large numbers of foamy mac rophages within the alveoli and interstitium, prominent subpleural and peri bronchiolar aggregates of histiocytes, and a few scattered lymphoid nodules . Numerous fungal organisms were evident within the cytoplasm of macrophage s on impregnation of histologic sections with the aforementioned stains. Ot her inciting agents were not identified. A third opossum lacked pulmonary l esions, but had similar organisms within one auricular sebaceous gland/hair follicle without apparent reaction to the organisms. Conclusion: A fungal agent was associated with granulomatous pneumonia in t he opossum, and comparison was made with endogenous lipid pneumonia previou sly described in opossums. These findings stress the importance of use of s pecial stains and additional diagnostic techniques when prominent alveolar macrophage accumulation is present on histologic examination of the opossum lung.