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 macrophages within the alveoli and interstitium, prominent subpleural and peribronchiolar aggregates of histiocytes, and a few scattered lymphoid nodules. Numerous fungal organisms were evident within the cytoplasm of macrophages on impregnation of histologic sections with the aforementioned stains. Other inciting agents were not identified. A third opossum lacked pulmonary lesions, 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 the opossum, and comparison was made with endogenous lipid pneumonia previously described in opossums. These findings stress the importance of use of special stains and additional diagnostic techniques when prominent alveolar macrophage accumulation is present on histologic examination of the opossum lung.