PCR-based ELISA technique for malaria diagnosis of specimens from Thailand.

We performed a field evaluation of polymerase chain reaction (PCR)-based enzyme-linked immunosorbent assays (ELISA) for the diagnosis of malaria. A commercially available PCR-ELISA microplate hybridization (MPH) assay was used. Blood specimens were collected from 300 volunteers seeking care at malaria clinics in Thailand. Examination of 200 high power fields by Giemsa-stained thick and thin smear (GTTS) revealed 51 P. falciparum (Pf), 45 P. vivax (Pv), seven mixed Pf-Pv infections. These plus a random sample of 48 GTTS-negative specimens were selected for this study. All 151 specimens were processed for parasite DNA extraction and assayed by PCR-MPH. The target DNA sequence of the 18S small subunit ribosomal RNA (SSUrRNA) gene was amplified by PCR and hybridized with species-specific probes for Pf, Pv, P. malariae (Pm) and P. ovale (Po) immobilized in the wells of the microtiter plate and detected by colorimetric assay. Colour development was assessed at an optical density (OD) of 405 nm. An absorbance reading of greater than or equal to 0.1 was used as a positive cut-off. In comparison with GTTS results, PCR-MPH sensitivity was 91.4% (53/58, 95% CI 84.2-98.6) for Pf, 94.2% (49/52, 87.9-100) for Pv and specificity was 95.8% (46/48, 95% CI 90.2-100). There was statistically significant positive correlation between parasite densities less than or equal to 7000/mul blood and absorbance reading, suggestive of PCR-MPH being semiquantitative. PCR-MPH also detected additional Pf and Pv cases as well as Pm and Po.