Herpes simplex encephalitis in a captive black howler monkey (Alouatta caraya)

An 18-month-old captive black howler monkey (Alouatta caraya) died after a 3-day history of neurologic signs. Gross findings at autopsy were limited to bloody, yellow, and foul-smelling intestinal contents. Histologically, there was extensive necrotizing meningoencephalitis predominantly in both cerebral hemispheres, and lymphohistiocytic, neutrophilic infiltrate expanded the subarachnoid and Virchow-Robbin space. In the most severely affected regions, neurons contained eosinophilic intranuclear inclusion bodies surrounded by a clear halo and margination of the chromatin. Electron microscopy of the affected cells revealed numerous intranuclear viral particles characteristic of herpesvirus. Immunohistochemically, neurons and glial cells in the affected regions were labeled with a monoclonal antibody against Human herpesvirus 1, and was confirmed by polymerase chain reaction.