Pulmonary lesions in Virginia opossums ( Didelphis virginiana ): Characterizing fungal pneumonia associated with Purpureocillium lilacinum

Several pulmonary lesions have been described in Virginia opossums (Didelphis virginiana), but fungal pneumonia in this species is largely unrecognized. We retrospectively analyzed gross and histologic pulmonary findings in 28 opossums from Louisiana. Lung sections were evaluated for fungal organisms, associated histologic changes, and other concurrent pulmonary lesions. Seventy-five percent of opossums (21/28) had pulmonary fungal organisms, and gross lesions were characteristic, consisting of patchy to generalized, indistinct, pinpoint, light-yellow parenchymal foci. These areas corresponded to alveoli filled with foamy macrophages and multinucleated giant cells that contained distinctive intracytoplasmic budding cells, which were 3 to 5 × 2 µm, ovoid to elongate, and argyrophilic, as well as rare pleomorphic fungal hyphae. Purpureocillium lilacinum was identified based on pulmonary fungal isolation and/or fungal internal transcribed spacer 2 (ITS-2) polymerase chain reaction (PCR) and sequencing in a subset of cases. Other findings included verminous pneumonia (13/28, 46%), pulmonary neoplasms (7/28, 25%), bacterial pneumonia (5/28, 18%), and endogenous lipid pneumonia (2/28, 7%). The histologic severity of fungal infections was significantly positively correlated with gross lesion severity and abundance of alveolar macrophages (P-values both < .0001). Identification of fungal pneumonia was as likely as verminous pneumonia, and fungal pneumonia was significantly more severe in opossums with concurrent verminous pneumonia (P = .0011). Despite the pulmonary changes, respiratory signs were rarely noted, even in severely affected cases. This is the first report associating P. lilacinum with fungal pneumonia in opossums from Louisiana. The characteristic gross and histologic lesions should prompt diagnosticians to closely evaluate for fungal organisms and consider P. lilacinum as a differential diagnosis.