Detection and species determination of malaria parasites by PCR: Comparison with microscopy and with ParaSight-F and ICT malaria Pf tests in a clinical environment

A rapid procedure for the diagnosis of malaria infections directly from dri ed blood spots by PCR amplification was evaluated with samples from 52 pati ents. Plasmodium infections were identified,with a genus-specific primer se t, and species differentiation between Plasmodium falciparum and Plasmodium vivax was analyzed by multiplex PCR. The PCR test with any of the three pr imer sets was able to detect as few as four parasites per microliter by gel electrophoresis or by nonisotopic paper hybridization chromatography. The diagnoses obtained by PCR correlated closely with those obtained by Giemsa staining except for two samples observed to have mixed P. falciparum-P. viv ax infections. These were initially missed by microscopic analysis. In comp arison with antigen-capture assays for P. falciparum, the PCR assays were a ble to detect three infections that were missed by the ParaSight-F test. Th e PCR test was negative for nine ParaSight-F-positive samples and one ICT M alaria Pf-positive sample, and these were confirmed to be false-positive re sults. The PCR thus gave no false-negative or false-positive results. Patie nts undergoing antimalarial therapy were also monitored by the PCR assay. F our of seven patients who were PCR positive for P. I vivax at the time of d ischarge were later readmitted to the hospital with a recurrence of P. viva x infection. We would like to propose that PCR is a sensitive and easy meth od that can serve as a useful addition to microscopy for the diagnosis and the clinical monitoring of treatment of malaria.