Abstract: Objective To confirm the diagnosis of a human case with atypical vivax-malaria from Yunnan Province by molecular technique. Methods DNA was extracted from blood films of unidentified sample， and of four known Plasmodium species （P. vivax， P. falciparum， P. knowlesi， and P. cynomolgi）. A DNA-based diagnosis with the poly-merase chain reaction （PCR） method targeting the small subunit ribosomal RNA （SSU rRNA） genes of genus- and species-specific （two human malaria species and P. knowlesi） was introduced. Results The PCR amplification with primer pair specific for P. knowlesi produced a single fragment of 150 bp. Sequence analysis showed that the amplified fragment was identical to the sequence of P. knowlesi. Conclusion The patient was naturally infected with P. knowlesi.

Key words: Plasmodium knowlesi, Natural infection, Human, SSU rRNA