Encephalitis in Two Porcupines Due to Baylisascaris Larval Migration

Abstract

Encephalitis is associated with the migration of Baylisascaris sp. larvae in a number of animal species, including mice, squirrels, woodchucks, rabbits, foxes, various birds, and humans. The species of Baylisascaris most often incriminated has been B. procyonis from raccoons. In a recent report of Baylisascaris sp. infection in American porcupines (Erethizon dorsatum) with concurrent Toxoplasma infection, the relative contribution of the 2 agents to the clinical problem could not be determined. In the current report, we describe the clinical signs, microscopic lesions, and epidemiologic investigation of Baylisascaris sp. infection causing progressive central nervous system (CNS) disease in 2 captive American porcupines. One porcupine also had bronchointerstitial pneumonia due to a virus that had not been previously reported in this species. An immature male porcupine developed ataxia, somnolence, rear limb paresis, and head tilt. Antibiotic therapy was initiated, but the animal died several weeks later, following a protracted course of progressive neurologic dysfunction. No gross lesions were observed at necropsy. Formalin-fixed tissues were submitted to the Animal Disease Diagnostic Laboratory, Purdue University, for microscopic evaluation. All sections of CNS tissue examined, including the cerebrum, cerebellum and brainstem, had multifocal malacia and encephalitis. The inflammatory infiltrate consisted predominantly of gemistocytic astrocytes, with scattered neutrophils, eosinophils, and rare multinucleated giant cells. The infiltrate was predominantly perivascular, including meningeal and submeningeal vessels of the cerebellum. The lung had a diffuse bronchointerstitial pneumonia characterized by large numbers of neutrophils filling bronchi, bronchioles, and alveolar spaces. Additionally, proteinaceous fluid filled many alveolar spaces, and dissolution of the alveolar walls was commonly observed (Fig. 1). Many alveolar epithelial cells contained large basophilic intranuclear inclusions (Fig. 2). Electron microscopic examination of lung tissue revealed numerous viral particles within the cytoplasm and nucleus of degenerate alveolar epithelial cells (Fig. 3). These viral particles were icosahedral and were approximately 30 nm in diameter. Based upon the morphology and size, these virus particles were presumed to be either a parvovirus or a picornavirus. Fresh lung tissues were not available for virus isolation. There has been 1 report of suspected parvovirus in porcupines; however, this was associated with necrotizing enteritis, and virions were not identified within inclusions. The liver was the only other organ examined that had morphologic lesions. Centrilobular hepatocytes had vacuolar