USE OF THE POLYMERASE CHAIN-REACTION TO DIRECTLY DETECT MALARIA PARASITES IN BLOOD-SAMPLES FROM THE VENEZUELAN AMAZON

We have examined the reproducibility, sensitivity, and specificity of detecting Plasmodium falciparum using the polymerase chain reaction (P CR) and the species-specific probe pPF14 under field conditions in the Venezuelan Amazon. Up to eight samples were field collected from each of 48 consenting Amerindians presenting with symptoms of malaria. Sam ple processing and analysis was performed at the Centro Amazonico para la Investigacion y Control de Enfermedades Tropicales Simon Bolivar. A total of 229 samples from 48 patients were analyzed by PCR methods u sing four different P. falciparum-specific probes. One P. vivax-specif ic probe and by conventional microscopy. Samples in which results from PCR and microscopy differed were reanalyzed at a higher sensitivity b y microscopy. Results suggest that microscopy-negative, PCR-positive s amples are true positives, and that microscopy-positive and PCR-negati ve samples are true negatives. The sensitivity of the DNA probe/PCR me thod was 78% and its specificity was 97%. The positive predictive valu e of the PCR method was 88%, and the negative predictive value was 95% . Through the analysis of multiple blood samples from each individual, the DNA probe/PCR methodology was found to have an inherent reproduci bility that was highly statistically significant.