Re-assessing thermal response of schistosomiasis transmission risk: evidence for a higher thermal optimum than previously predicted

The geographical range of schistosomiasis is affected by the ecology of schistosome parasites and their obligate host snails, including their response to temperature. Previous models predicted schistosomiasis' thermal optimum at 21.7 degree, which is not compatible with the temperature in sub-Saharan regions where schistosomiasis is hyperendemic. We performed an extensive literature search for empirical data on the effect of temperature on physiological and epidemiological parameters regulating the free-living stages of S. mansoni and S. haematobium and of their obligate host snails, i.e., Biomphalaria spp. and Bulinus spp., respectively. We derived nonlinear thermal responses fitted on these data to parameterize a mechanistic, process-based model of schistosomiasis. We then re-cast the basic reproduction number, and prevalence of schistosome infection as functions of temperature. We found that the thermal optima for transmission of S. mansoni and S. haematobium range between 23.1-27.3 degrees and 23.6-27.9 degrees respectively. We also found that the thermal optimum shifts toward higher temperatures as the human water contact rate increases with temperatures. Our findings line up with an extensive dataset of schistosomiasis prevalence data in sub-Sharan Africa. The refined nonlinear thermal-response model developed here suggests a more suitable current climate and a greater risk of increased transmission with future warming. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work is funded by the Stanford Center for Innovation in Global Health, Belmont Forum on 503 Climate Environment and Health, UKRI (UK), FAPESP (Brazil), PASRES (Cote d' Ivorie), and the USA National Science 504 Foundation (DEB-2024383; DEB-2011147; DEB 2011179, Belmont CEH/NSF ICER-2024383). EAM was funded by the 505 National Science Foundation (DEB-2011147 with Fogarty International Center), the National Institutes of Health 506 (R35GM133439, R01AI168097, R01AI102918), and the Stanford Center for Innovation in Global Health and Woods In 507 stitute for the Environment ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. 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, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The authors are also particularly grateful to Dr. Penelope Vounatsou (Swiss TPH), the 508 curator of the GNTD dataset.