Laboratory Detection of Artemisinin-Resistant Plasmodium falciparum

• Published in: Antimicrobial agents and chemotherapy Vol. 58; no. 6; pp. 3157 - 3161
• Main Authors: CHOTIVANICH, Kesinee, TRIPURA, Rupam, DAS, Debashish, YI, Poravuth, DAY, Nicholas P. J, PUKRITTAYAKAMEE, Sasithon, CHAR MENG CHUOR, SOCHEAT, Duong, DONDORP, Arjen M, WHITE, Nicholas J
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.06.2014
• Subjects: Animals; Antibiotics. Antiinfectious agents. Antiparasitic agents; Antimalarials; Antimalarials - pharmacology; Artemisinins; Artemisinins - pharmacology; Artesunate; Biological and medical sciences; Drug Resistance; Half-Life; Malaria, Falciparum - blood; Malaria, Falciparum - parasitology; Medical sciences; Parasitic Sensitivity Tests; Pharmacology. Drug treatments; Phenotype; Plasmodium falciparum; Plasmodium falciparum - drug effects; Plasmodium falciparum - growth & development; Susceptibility; Resistance; Protozoa; Antimalarial; Plasmodium falciparum; Apicomplexa; Artemisinin; Parasiticide; Diagnosis; Laboratory; Detection
• ISSN: 0066-4804; 1098-6596
• DOI: 10.1128/AAC.01924-13

Conventional 48-h in vitro susceptibility tests have low sensitivity in identifying artemisinin-resistant Plasmodium falciparum, defined phenotypically by low in vivo parasite clearance rates. We hypothesized originally that this discrepancy was explained by a loss of ring-stage susceptibility and so developed a simple field-adapted 24-h trophozoite maturation inhibition (TMI) assay focusing on the ring stage and compared it to the standard 48-h schizont maturation inhibition (WHO) test. In Pailin, western Cambodia, where artemisinin-resistant P. falciparum is prevalent, the TMI test mean (95% confidence interval) 50% inhibitory concentration (IC50) for artesunate was 6.8 (5.2 to 8.3) ng/ml compared with 1.5 (1.2 to 1.8) ng/ml for the standard 48-h WHO test (P = 0.001). TMI IC50s correlated significantly with the in vivo responses to artesunate (parasite clearance time [r = 0.44, P = 0.001] and parasite clearance half-life [r = 0.46, P = 0.001]), whereas the standard 48-h test values did not. On continuous culture of two resistant isolates, the artemisinin-resistant phenotype was lost after 6 weeks (IC50s fell from 10 and 12 ng/ml to 2.7 and 3 ng/ml, respectively). Slow parasite clearance in falciparum malaria in western Cambodia results from reduced ring-stage susceptibility.