Fatal amoebic meningoencephalitis caused by Balamuthia mandrillaris in Pongo pygmaeus and first case report in Pan troglodytes verus

<i>Balamuthia mandrillaris</i> is an amoeba that can cause granulomatous amoebic encephalitis (GAE) as well as lung and skin infections in both humans and animals. Studies on <i>B. mandrillaris</i>-related GAE cases have increased in recent years. This amoeba has been identified as a cause of encephalitis and death in several non-human primates. In this study, we report a case of a 4-year-old female Bornean orangutan (<i>Pongo pygmaeus</i>) in a zoological center that exhibited neurological symptoms for several days. After unsuccessful treatments and a worsening in her condition, euthanasia was deemed necessary. Additionally, we describe the case of a 4-year-old male chimpanzee (<i>Pan troglodytes verus</i>) who died suddenly in a different zoo. Postmortem analysis revealed brain lesions with multiple hemorrhages, oedema, and inflammation in various organs in both cases. Histology showed the presence of <i>B. mandrillaris</i> trophozoites in necrotic and inflamed brain tissues, consistent with granulomatous amoebic meningoencephalitis. The diagnosis was confirmed using a multiplex qPCR assay on brain tissue samples from both animals water and soil samples from the chimpanzee's and orangutan's enclosure tested positive for <i>B. mandrillaris</i> DNA by qPCR, confirming environmental exposure. An immunofluorescent antibody (IFA) assay detected <i>B. mandrillaris</i> in chimpanzee brain slices. According to the authors' knowledge, this report documents the first known cases of <i>Balamuthia</i> amoebic encephalitis in non-human primates in Spain and the first case in <i>Pan troglodytes verus</i>.