Fatal human herpesvirus type 1 infection in a white-handed gibbon (Hylobates lar)

This report documents a case of spontaneous, fatal, and likely recrudescent human herpesvirus type 1 (HHV-1) infection in a captive white-handed gibbon (Hylobates lar) confirmed by polymerase chain reaction (PCR). An approximately 44-year-old, captive, female, white-handed gibbon with a history of recurrent conjunctivitis and occasional seizures became acutely weak, disoriented, and ataxic. A postictal state was suspected by caretakers and veterinary staff, and euthanasia was ultimately elected because of lack of clinical improvement with supportive care. No significant abnormalities were detected at necropsy. Histologically, sections of cerebrum and midbrain contained minimal to mild, multifocal lymphoplasmacytic meningoencephalitis with numerous intranuclear viral inclusions within astrocytes and some neurons. The presumptive diagnosis of HHV-1-induced encephalitis was strengthened by nested PCR amplification of a segment of the herpesvirus DNA polymerase gene. Sequences from this region have been found to be unique to each herpesvirus species, thus identifying HHV-1 as the likely etiologic agent in this case. Positive HHV-1 serology from several years before the terminal episode suggested that the disease was most likely due to recrudescence of latent HHV-1 infection.