An exploratory study to assess the influence of schistosomiasis on the occurrence of dengue virus in Madagascar.

BACKGROUND: Dengue virus (DENV) is the most prevalent mosquito-borne virus worldwide, with approximately half of the world's population at risk of infection. Although it has been shown that parasitic infections can influence viral co-infections the role of schistosomiasis has not yet been explored. The objective of this exploratory study was to investigate the influence of schistosome infection on DENV infection in Madagascar. METHODS: Between March 2020 and October 2022 we recruited participants in the regions of Boeny and Atsinanana to assess the seroprevalence of DENV in the country using highly specific tests for the detection of IgG antibodies and investigated the influence of schistosome infections on DENV infections through a plaque reduction neutralisation test (PRNT). For this, additional participants were recruited in Haute Matsiatra between July 2022 and March 2023, Poisson regression models were used to assess the association of the PRNT results with schistosome infections. RESULTS: For the first time, we report a low seroprevalence of DENV (up to 3.3%) in areas with a high prevalence (> 50%) of schistosome infection. Additionally, we could demonstrate that sera derived from schistosome-infected individuals exert a significant antiviral activity against DENV infection (up to 27.5%). A Poisson regression analysis revealed that, among the possible factors assessed, the schistosome infection status was the only factor associated with the inhibitory effects against DENV infection in the PRNT. Finally, we could observe that highest IgE level were found in participants showing the greatest reduction in viral infection in the PRNT. CONCLUSIONS: Our data suggest that schistosomiasis might play a protective role against DENV infections. These findings offer new perspectives regarding how chronic parasitic infections affect the dynamics of DENV infections in Africa.