Cerebral Hirano-like bodies in an alpaca (Vicugna pacos): histologic and ultrastructural characterization

A 14-year-old female alpaca (Vicugna pacos) was presented with a 1-week history of lethargy and anorexia and a 2-day history of recumbency, trembling, and hypothermia. There were no significant gross findings on postmortem examination. Hematoxylin and eosin-stained sections of brain demonstrated the presence of intracytoplasmic crystalline eosinophilic rod-shaped inclusions, mainly in the hippocampal pyramidal cells. Immunohistochemical staining for synuclein, tau protein, ubiquitin, and smooth muscle actin was negative. All inclusions were positive with phosphotungstic acid hematoxylin. Ultrastructurally, the inclusions were multilamellar and filamentous with longitudinal herringbone pattern and cross-sectional latticelike structure. The combination of hematoxylin and eosin appearance, special stains, immunostaining, and ultrastructural findings was consistent with Hirano-like bodies. The Hirano-like bodies were highly unlikely to be the cause of the neurologic signs experienced by this alpaca. To the authors' knowledge, this is the first report of spontaneous cerebral Hirano-like bodies in an alpaca.