Suspicion of epizootic Lawsonia intracellularis disease in a group of pileated gibbons ( Hylobates pileatus )

Within a month, all five individuals of a pileated gibbon ( Hylobates pileatus ) family presented the same symptoms: diarrhoea, vomiting and severe apathy. During this first outbreak, three of them died acutely and a fourth died during another outbreak 7 months later. Extensive virology, bacteriology and parasitology undertaken on faeces did not reveal any pathogen. Haematology and extensive biochemistry did not demonstrate any obvious medical disorder. Necropsy revealed a severe proliferative enteropathy, and rare argyrophilic bacteria were noted within the lumen of hyperplastic colonic glands on histology with silver staining. Specific faecal PCR was positive for Lawsonia intracellularis infection. These combined elements led to a strong suspicion of L intracellularis epizooty, despite the absence of large numbers of argyrophilic bacteria, as usually expected in this disease process. L intracellularis has mostly been described in pigs even if reported in a broad range of mammalian species including primates. L intracellularis may be underdiagnosed in zoos as it requires a faecal PCR for identification and silver staining for histological visualisation.