Persistent intestinal schistosomiasis and progressive liver fibrosis in semi-captive chimpanzees: a 12-year epidemiological follow-up in Ngamba Island Chimpanzee Sanctuary, Lake Victoria, Uganda

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Abstract In 2010, intestinal schistosomiasis, caused by Schistosoma mansoni infection, was first confirmed within semi-captive chimpanzees ( Pan troglodytes ) on Ngamba Island, Lake Victoria. Since then, and despite repeated praziquantel treatments, there is ongoing evidence of reinfection. Conducting a comprehensive contemporary appraisal, we implemented a multi-modal diagnostic approach combining coprological, urine antigen-based and semi-invasive parasitological assays, augmented by standardized hepatic ultrasonography. We reassessed 49 chimpanzees to reveal persistent infections (urine-antigen prevalence was 36.7% although fecal egg-patency was 4.1%), often with progressive schistosomiasis-associated hepatic morbidity, noting overt pipe-stem fibrosis in certain animals. Molecular DNA analyses of retrieved schistosome eggs and larvae confirmed the presence of S. mansoni alone. Sequence analysis of the mitochondrial cytochrome oxidase subunit 1 provided a snapshot of current schistosome genetic diversity. Three previously identified haplotypes were recovered alongside 2 additional haplotypes newly detected locally. These latter haplotypes, likely having a Kenyan ancestry, were suspected to have been introduced recently. We draw attention to the limitations of chemotherapy-only control and highlight future needs to gain better environmental control within this lakeshore sanctuary setting.

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