Entamoebiasis in zoological non-human primates in the United Kingdom.

Entamoebiasis is a significant disease in non-human primates (NHPs), causing a spectrum of clinical presentations ranging from asymptomatic carriage to severe, necrotizing colitis and life-threatening extraintestinal dissemination. This study examined entamoebiasis in captive NHPs across nine zoological collections from 2004 to 2020. A total of 28 cases, spanning nine Old World (OW) and four New World (NW) primate species, were confirmed via histopathology and Entamoeba histolytica immunohistochemistry. Entamoebiasis caused intra- and extraintestinal disease, including necrotizing colitis and hepatitis, with characteristic gross and histological lesions including well-demarcated transmural 'flask-like' mucosal ulceration and necrotizing hepatitis with intralesional amoebic trophozoites. Rare cases presented with pneumonia, peritonitis and orchitis. OW primates, particularly Colobinae species, were more frequently affected. This study expands the known host range of entamoebiasis providing the first reports in emperor tamarin (Saguinus imperator), king colobus (Colobus polykamos), grizzled leaf (Presbytis comata), black howler (Alouatta caraya), brown spider (Ateles hybridus) and white-faced saki (Pithecia pithecia) monkeys. No seasonal trends were observed, and cases involved both sexes and all age groups, predominantly adults. Species-specific differences were noted, with OW primates having more frequent transmural colitis. These findings emphasize the importance of entamoebiasis in differential diagnoses for NHPs with gastrointestinal signs, and include recommendations for routine collection of fresh, frozen and formalin-fixed tissues during necropsy, prioritizing gastrointestinal and hepatic samples. Regular health assessments and surveillance for Entamoeba species in NHPs are crucial for detecting subclinical carriers, enabling early, targeted interventions and minimizing negative impacts on NHP populations and conservation efforts.