Dermal trypanosomes in suspected and confirmed cases of gambiense Human African Trypanosomiasis

Background The diagnosis of Human African Trypanosomiasis (HAT) typically involves two steps: a serological screen, followed by the detection of living trypanosome parasites in the blood or lymph node aspirate. Live parasites can, however, remain undetected in some seropositive individuals, who we hypothesize are infected with Trypanosoma brucei gambiense parasites in their extravascular dermis. Methods and findings To test this hypothesis, we conducted a prospective observational cohort study in the gambiense HAT (gHAT) focus of Forecariah, in the Republic of Guinea. 5,417 subjects in this disease foci underwent serological screening for gHAT. Of these individuals, 66 were enrolled into our study, of whom 40 were seronegative, 8 were seropositive but unconfirmed, and 18 confirmed gHAT cases. Enrolled individuals underwent a dermatological examination, and had blood samples and skin biopsies taken and examined for trypanosomes by molecular and immuno-histological methods. In confirmed cases, dermatological symptoms were significantly more frequent, relative to seronegative controls. T. b. gambiense parasites were present in the blood of all confirmed cases but not in unconfirmed seropositive individuals. However, trypanosomes were detected in the dermis of all unconfirmed seropositive individuals and confirmed cases. After 6 and 20 months of treatment, dermal trypanosome numbers in skin biopsies of confirmed cases progressively reduced. Conclusions Our results thus highlight the skin as a potential reservoir for trypanosomes, with implications for our understanding of this disease’s epidemiology in the context of its planned elimination and highlighting the skin as a novel target for gHAT diagnostics. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by the Wellcome Trust (209511/Z/17/Z), the Institut de Recherche pour le Développement, the Institut Pasteur, the French Government Investissement d’Avenir programme - Laboratoire d’Excellence “Integrative Biology of Emerging Infectious Diseases” (ANR-10-LABX-62-IBEID) and the French National Agency for Scientific Research (projects ANR-14-CE14-0019-01 EnTrypa and ANR-18-CE15-0012 TrypaDerm). None of these funding sources has a direct scientific or editorial role in the present study. ### Author Declarations All relevant ethical guidelines have been followed; any necessary IRB and/or ethics committee approvals have been obtained and details of the IRB/oversight body are included in the manuscript. Yes All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Upon request, the original protocol and associated forms, as well as an anonymised dataset, could be obtained from the corresponding author rotureau{at}pasteur.fr.