Genomic investigation of a non-travel Plasmodium falciparum case linked to imported malaria in China’s post-elimination era

Abstract

Background: Although China has achieved malaria elimination, the risk of reintroduction persists due to imported Plasmodium falciparum cases. Occasional infections without a clear travel history present challenge to routine epidemiological investigation and underscore the need for advanced tracing tools. Methods: Whole-genome sequencing (WGS), principal component analysis (PCA), and identity-by-descent (IBD) analysis were applied to investigate a P. falciparum case reported in Chongqing, China, in 2019. The patient had no overseas travel history but was treated at the same hospital with a confirmed imported case from the Democratic Republic of the Congo (DRC). Results: Genomic analysis placed the unidentified case within the West and Central African parasite cluster. IBD analysis showed a high degree of relatedness (IBD = 0.9) between this case and the DRC-imported case, suggesting a potential transmission link. These findings indicate the likely Central African origin of the infection and raise concerns about local transmission risk even in a post-elimination setting. Discussion: This case highlights the limitations of traditional epidemiology in detecting cryptic transmission routes. Genomic epidemiology enables finer-scale resolution of parasite origin and relatedness, providing critical evidence in elimination-phase malaria control. Conclusions: Genomic tools such as WGS, PCA, and IBD analysis can enhance national malaria surveillance systems by identifying infection sources and clarifying transmission routes. Their integration supports elimination-stage strategies and helps prevent malaria reintroduction in formerly endemic regions.