ABSTRACT
In vitro drug susceptibility profiles were assessed in 75 Plasmodium falciparum isolates from 4 sites in Myanmar. Except at Mawlamyine, the site closest to the Thai border, prevalence and degree of resistance to mefloquine were lower among the Myanmar isolates as compared with those from Thailand. Geometric mean concentration that inhibits 50% (IC50) and 90% (IC90) of Mawlamyine isolates were 51 nM (95% confidence interval [CI], 40-65) and 124 nM (95% CI, 104-149), respectively. At the nearest Thai site, Maesod, known for high-level multidrug resistance, the corresponding values for mefloquine IC50 and IC90 were 92 nM (95% CI, 71-121) and 172 nM (95% CI, 140-211). Mefloquine susceptibility of P. falciparum in Myanmar, except for Mawlamyine, was consistent with clinical-parasitological efficacy in semi-immune people. High sensitivity to artemisinin compounds was observed in this geographical region. The data suggest that highly mefloquine-resistant P. falciparum is concentrated in a part of the Thai-Myanmar border region.
Subject(s)
Antimalarials/pharmacology , Artemisinins , Plasmodium falciparum/drug effects , Animals , Chloroquine/pharmacology , Drug Resistance , Mefloquine/pharmacology , Parasitic Sensitivity Tests , Sesquiterpenes/pharmacologyABSTRACT
We performed a field evaluation of polymerase chain reaction (PCR)-based enzyme-linked immuno-sorbent 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 > or = 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 < or = 7000/microl 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.
Subject(s)
Enzyme-Linked Immunosorbent Assay/methods , Malaria, Falciparum/diagnosis , Malaria, Vivax/diagnosis , Polymerase Chain Reaction/methods , Adolescent , Adult , Aged , Child , Child, Preschool , Colorimetry , Female , Humans , Male , Middle Aged , Sensitivity and Specificity , ThailandABSTRACT
We assessed a rapid, Plasmodium falciparum histidine rich protein 2 (PfHRP2)-based immunochromatographic test (ICT Malaria Pf Test), for detection of asexual P. falciparum parasitemia in 551 subjects in three groups: (1) symptomatic patients self-referring for diagnosis, (2) villagers in a screening survey, and (3) patients recently treated for P. falciparum malaria. Expert light microscopy was the reference standard. ICT test performance was similar for diagnostic and screening modes. Four findings emerged: (1) test sensitivity correlated directly with parasite density, (2) test band intensity correlated directly with parasite density, (3) persistent test positivity after parasite clearance precludes its use for monitoring early therapeutic responses, and (4) a false negative test at 18,000 parasites/microl is unexplained. We conclude that a strong positive ICT test is highly predictive of falciparum asexual parasitemia for the diagnosis of new cases of falciparum malaria in Thailand, but a negative test result is inadequate to exclude parasitemia < 300/microl, and in some instances, even a higher parasitemia.
Subject(s)
Chromatography/methods , Immunoassay/methods , Malaria, Falciparum/diagnosis , Parasitemia/diagnosis , Plasmodium falciparum/isolation & purification , Adult , Animals , Evaluation Studies as Topic , Female , Humans , Malaria, Falciparum/parasitology , Male , Microscopy , Parasitemia/parasitology , Plasmodium falciparum/growth & development , Proteins/analysis , Proteins/immunology , Protozoan Proteins/analysis , Protozoan Proteins/immunology , Reagent Kits, Diagnostic , ThailandABSTRACT
Reported are the in vitro susceptibilities of Plasmodium falciparum to artesunate, mefloquine, quinine and chloroquine of 86 isolates and to dihydroartemisinin of 45 isolates collected from areas of high resistance to mefloquine within Thailand near the borders with Myanmar and Cambodia, and from southern Thailand where P. falciparum is generally still sensitive to mefloquine. All the isolates were highly sensitive to artesunate, but the geometric mean IC50S were higher in isolates from the Thai-Myanmar and Thai-Cambodian borders than in those from southern Thailand. The IC50S for mefloquine and artesunate were strongly correlated (Pearson r = 0.605; n = 86; P < 0.00001). As expected, the in vitro sensitivities to dihydroartemisinin and artesunate were similar and strongly correlated (at IC50, Pearson r = 0.695; n = 45; P < 0.00002). The correlation between the activity of mefloquine and artesunate requires further investigation in order to determine the potential for development of cross-resistance in nature. Our results suggest that combination with mefloquine is not the ideal way of protecting the usefulness of artemisinin and its derivatives. A search for more suitable partner drugs to these compounds and careful regulation of their use are necessary in the interest of ensuring their long therapeutic life span.
