Monitoring drug resistance in Plasmodium falciparum clinical isolates collected from Northern Thailand

Background

Drug resistance developed by P. falciparum is a real threat to malaria disease control and treatment. Recent reports from the Thai-Cambodia and Thai-Myanmar borders have described the artemisinin resistance developed by the parasite. Therefore, there is a need to monitor emergence of resistance parasites in order to limit their spread.

Materials and methods

Clinical isolates were collected from patients infected with P. falciparum. The parasites were adapted in in vitro culture and tested for 50% inhibitory concentration (IC₅₀) against pyrimethamine (Pyr), chloroquine (CQ), mefloquine (MQ) and dihydroartemisinin (DHA) using standard malaria SYBR Green I-based fluorescence (MSF) assay. Mutations of genes associated with drug resistance were also investigated.

Results and conclusions

All the tested clinical isolates were resistant to Pyr and CQ, even though Pyr was not used in the area for a long time, while CQ is still used to treat P. vivax infection. Only some of the isolates were resistant to MQ, while all of them were sensitive to DHA using standard drug sensitivity assay. Pyr- and CQ-resistant isolates contained mutations at dihydrofolate reductase (Pfdhfr) and chloroquine resistance transporter (Pfcrt) genes as expected. The results confirm the existence of drug resistance parasites and suggest the use of proper drugs for malaria treatment in the field.