Encephalic Toxoplasm in a White-Eared Possum (Didelphis albiventris)

Background: Toxoplasmosis is caused by Toxoplasma gondii, an obligate intracellular protozoan that belongs to the Aplicomplexa phylum, coccidian subclass, and affects all warm-blooded animals. The role of opossums in the epidemiology of toxoplasmosis in Brazil is not fully understood, and there are very few descriptions of toxoplasmosis lesions in these animals. This report describes the anatomopathological, molecular and immunohistochemical findings of a case of encephalic toxoplasmosis in free-living white-eared possum (Didelphis albiventris).Case: A young male opossum (D. albiventris), was treated at the Veterinary Hospital of Wild Animals of the University of Brasília, Federal District. The animal was apathetic, uncoordinated, reluctant to move, and had an exposed proximal fracture in the left radius and ulna with laceration of muscles and adjacent tendinous structures. Amputation on the left thoracic limb was performed followed by analgesia and antibiotic therapy. The environment is frequented by other wild animals, and stray cats have access to the patio of the building. Twenty-five days after arriving at the hospital, the animal was found dead in its cage. After death, a necropsy was performed. Organ fragments from the abdominal cavity, thoracic and central nervous system were collected, processed routinely for histology and stained with hematoxylin and eosin. Macroscopic lesions in the central nervous system were not observed. On microscopy, the brain showed moderate random glial nodules throughout the neuropil associated with the presence of spherical to elongated parasitic cysts of about 20 µm, with a thin wall and with its interior full of bradyzoites, consistent with Toxoplasma gondii. There was also moderate fibrinoid necrosis and moderate multifocal lymphoplasmacytic infiltrate surrounding the blood vessels (perivascular cuffs) To investigate the etiology of the brain injury, brain sections were subjected to immunohistochemistry (IHC) and real-time polymerase chain reaction (qPCR) technique for detection of T. gondii and Neospora caninum. Immunostaining for T. gondii in the cyst wall and in bradyzoites and negative immunostaining for N. caninum. qPCR was positive for T. gondii and negative for N. caninum.Discussion: Diagnosis of encephalic toxoplasmosis in a Didelphis albiventris was possible based on histopathological, immunohistochemical and molecular findings. The morphological classification of the brain lesion was important for the diagn