Diagnosis of Plasmodium falciparum infection by spot hybridization assay: specificity, sensitivity, and field applicability.

The spot hybridization assay for the detection of Plasmodium falciparum reported here uses as probe a repetitive DNA sequence from this species and exhibits a high degree of species specificity. Isolates from African, Asian, and South American patients were positive in the assay and gametocytes could be detected at the same level of parasitaemia as asexual parasites. An RNA probe containing the same repetitive sequence as the DNA probe has a detection limit of 1 parasite per 10(6) red blood cells. Comparison of the results of the assay with those obtained by microscopic examination of blood films indicated that the assay was more sensitive than microscopy if the blood films were examined for only 10 minutes; however, 40 minutes' examination by microscopy was slightly more sensitive than the assay.