RegularPlasmodium falciparumimportation onto Bioko Island, Equatorial Guinea, hampers malaria elimination from the island
Authors: Stabler Thomas C. , Dwivedi Ankit , Guo Bing , Shrestha Biraj , Joshi Sudhaunshu , Rivas Matilde Riloha , Donfack Olivier Tresor , Guerra Carlos A. , García Guillermo A. , Daubenberger Claudia , Silva Joana C. 
Published: December 2024

The Bioko Island Malaria Elimination Project (BIMEP) has made significant progress in reducing the prevalence ofPlasmodium falciparumon Bioko Island, Equatorial Guinea. However, like other malaria endemic islands like São Tomé and Principe and Zanzibar, Tanzania, elimination efforts are hampered by imported infections. In an effort to understand the local transmission dynamics and the influence of importation on Bioko Island’sP. falciparumpopulation, whole-genome sequences were generated from field samples collected during the BIMEP’s 2019 Malaria Indicator Survey (MIS). Within the sub-Saharan African context, we observed Bioko Island parasites did not significantly differentiate from nearby continental neighbors. Among Bioko infections, within-host diversity and the quantity of polyclonal infections appear similar to an area of moderate malaria transmission. However, we observed higher than expected genetic diversity among Bioko parasites, similar to high transmission areas, suggesting imported strains are contributing to transmission on the island. Among Bioko’s closest geographical neighbors, the flow of parasites with Bioko appeared more pronounced with the Gabonese parasite population, implying more importation may be coming from this region than others. Overall, despite significant investment in malaria control, results illustrate the challenges of eliminating malaria without both interrupting local transmission and accounting for importation from higher transmission areas, likely due to human migration. For there to be sustained progress towards elimination, the BIMEP needs, if feasible, to conduct targeted interventions of outgoing/incoming travelers, and ideally expand malaria control interventions to the continental region of Equatorial Guinea.

Importance

Plasmodium falciparumaccounts for the majority of malaria deaths globally, with over 500,000 estimated deaths in 2023, predominantly in sub-Saharan Africa, despite strong investment in control and elimination interventions. Incorporating sequencing technologies into malaria surveillance is viewed as a powerful tool to improve control strategies, including identifying parasite transmission pathways. Here, we provide the first genomic characterization ofP. falciparumon Bioko Island and Equatorial Guinea since malaria control began in 2004, and use these data to better understand the contribution of neighboring regions to Bioko’sP. falciparumpopulation. Results highlight the need to account for offisland contributors to transmission and to understand how unmitigated transmission in neighboring regions can hamper progress. This study furthers our understanding of how the flow of parasites between regions impacts infectious disease control and provides foundational genomic data in a previously undescribed region that can be used to inform malaria elimination efforts.