Authors

A Juhasz³; LJ Cunningham³; C Graves³; J Rukondo⁵; T Mukungu²; D Oguttu¹; S Mpooya⁶; A Rugigana¹; F Besigye¹; EJ Lacourse⁴; JR Stothard⁴; JR Stothard⁴;  ¹ Vector Control Division, Ministry of Health, Uganda;  ² Vector Borne and Neglected Tropical Diseases Control Division, Ministry of Health, Uganda;  ³ Institute of Medical Microbiology, Semmelweis University,, Hungary;  ⁴ Tropical Disease Biology, Liverpool School of Tropical Medicine, Liverpool, UK, UK;  ⁵ Ngamba Island Chimpanzee Sanctuary / Chimpanzee Trust, Entebbe, Uganda;  ⁶ Republic of Uganda Ministry of Health, Kampala, Central Region, Uganda

Discussion

In 2010, intestinal schistosomiasis caused by Schistosoma mansoni was first confirmed in a semi-captive chimpanzee (Pan troglodytes) population on Ngamba Island, Lake Victoria, revealing sustained natural exposure of great apes to a hyper-endemic transmission setting. Despite repeated praziquantel (PZQ) treatment administered as part of routine veterinary care, evidence of ongoing infection has persisted within the population. Using a multi-modal diagnostic framework combining coprological, antigen-based and invasive parasitological assays alongside standardized hepatic ultrasonography, we assessed 49 chimpanzees. Results indicate a broadly stable infection prevalence as assessed by antigen detection, accompanied by a marked progression in schistosomiasis-associated hepatic morbidity. Ultrasonographic assessment revealed progression from mild periportal thickening to advanced pipe-stem fibrosis in several long-term residents over the 12-year interval. Molecular analysis showed the presence of only S. mansoni amongst with further analysis showing the persistence of three historic haplotypes plus an additional two, previously undescribed, haplotypes. These findings underscore the limitations of chemotherapy-only control strategies in great apes and emphasize the role of continuous environmental re-exposure in sustaining transmission within lacustrine One Health settings.