To diagnose the imported plasmodium malariae cases with nested-PCR amplification of 18SSUrRNA gene.

Plasmodium DNA was extracted from anticoagulant blood as template with the plasmodium gene-specific primers in the first round of amplification, then the products of the first round were amplified as the second round template.The results of different subgroups of plasmodium were acquired.The target fragment of PCR was used for species identification and sequencing, comparing with the control sample of P. vivax and P. falciarum.

By using the plasmodium gene-specific primers amplification, the fragments were amplified from the three samples with 1 200 bp.By using the interspecific primers amplification, specific fragments were amplified from the blood samples of P. vivax and P. falciarum with 120 bp and 205 bp respectively, and 144 bp from the suspicious patient with P. malariae specific primers.The suspicious patients did not have the specific fragment of P. ovale.The product of the suspicious patients was sequenced and compared with standard sequence registered in Genbank by blast.The comparison results showed that the fragment size and product sequence were in accordance with the reference.The results showed that nested PCR was more objective than the traditional microscopic examination.

The results indicate that nested PCR can be used to detect plasmodium with high specificity and identify plasmodium at the species level when microscopy is equivocal.The specific primers to amplify 18 SSUrRNA gene fragment can be used to diagnose plasmodium malariae infection.