A Plasmodium vivax Case Identified Solely via the Use of Next-Generation Sequencing

Accurate identification of Plasmodium species is essential for appropriate malaria management, particularly in cases of Plasmodium vivax (P. vivax), in which relapse prevention requires radical cure. A diagnostically challenging case of late-onset malaria in a Swedish woman presenting with tertian fever 5 months after travel to Indonesia is described. Although loop-mediated isothermal amplification repeatedly indicated Plasmodium infection, routine microscopy and multiple independent species-specific quantitative polymerase chain reaction (qPCR) assays failed to identify the infecting species. Conventional polymerase chain reaction and Sanger sequencing confirmed the presence of Plasmodium DNA but did not enable reliable species determination. Amplicon-based next-generation sequencing (NGS) targeting the small subunit ribosomal RNA (rRNA) gene generated more than 5,000 P. vivax reads. Sequence polymorphisms in primer/probe binding regions explained the failure of standard qPCR assays. After species identification and confirmation of normal G6PD activity, the patient received primaquine for hypnozoite eradication. This case highlights the diagnostic value of NGS in malaria and the limitations of relying solely on conserved 18S rDNA targets.