METHODS: This study investigated blood samples from malaria centres in Southern Thailand. Genetic loci associated with drug resistance were amplified and sequenced. Drug resistance associated genes Pvmdr1, Pvcrt-o, Pvdhfr, and Pvdhps were characterized for 145 cases of P. vivax malaria, as well as the artemisinin resistance-associated Pfkelch13 gene from 91 cases of P. falciparum malaria.
RESULTS: Plasmodium vivax samples from Southern Thai provinces showed numerous chloroquine and antifolate resistance-associated mutations, including SNP and Pvcrt-o K10-insertion combinations suggestive of chloroquine resistant P. vivax phenotypes. A high proportion of the C580Y coding mutation (conferring artemisinin resistance) was detected in P. falciparum samples originating from Ranong and Yala (where the mutation was previously unreported).
CONCLUSIONS: The results demonstrate a risk of chloroquine and antifolate resistant P. vivax phenotypes in Southern Thailand, and artemisinin resistant P. falciparum observed as far south as the Thai-Malaysian border region. Ongoing surveillance of antimalarial drug resistance markers is called for in Southern Thailand to inform case management.
AIM OF THE STUDY: In this context, supported with previous preliminary data of its antiplasmodial activity, this study was undertaken to determine the in vitro antiplasmodial and cytotoxicity activities of G. lanceolatus crude extracts and its major compounds.
MATERIALS AND METHODS: The in vitro antiplasmodial activity was determined by parasite lactate dehydrogenase (pLDH) assay on chloroquine-sensitive (3D7) and chloroquine-resistant (K1) strains of Plasmodium falciparum. The cytotoxicity activity was evaluated using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay on hepatocellular carcinoma (HepG2) and normal liver (WRL-68) cell lines.
RESULTS: The root methanol extract possessed potent antiplasmodial activity against both P. falciparum 3D7 and K1 strains (IC50 = 2.7 μg/ml, SI = 140; IC50 = 1.7 μg/ml, SI = 236). Apart from the DCM extract of stem bark and root that were found to be inactive (IC50 > 50 μg/ml) against 3D7 strain, all other tested crude extracts exhibited promising (5< IC50 30 µg/ml, CC50 > 10 µM, respectively), except for the hexane and DCM extracts of root, which exerted mild cytotoxicity on HepG2 cell line (IC50 falciparum. Further studies are being carried out to assess their toxicity profile and antimalarial efficacy in animal model.
METHODS: Plasmodium falciparum DNA was collected from the Thailand-Myanmar, Thailand-Malaysia and Thailand-Cambodia borders during 2008-2016 (N = 233). Semi-nested PCR and nucleotide sequencing were used to assess mutations in Plasmodium falciparum dihydrofolate reductase (pfdhfr), P. falciparum dihydropteroate synthase (pfdhps). Gene amplification of Plasmodium falcipaurm GTP cyclohydrolase-1 (pfgch1) was assessed by quantitative real-time PCR. The association between pfdhfr/pfdhps mutations and pfgch1 copy numbers were evaluated.
RESULTS: Mutations in pfdhfr/pfdhsp and pfgch1 copy number fluctuated overtime through the study period. Altogether, 14 unique pfdhfr-pdfhps haplotypes collectively containing quadruple to octuple mutations were identified. High variation in pfdhfr-pfdhps haplotypes and a high proportion of pfgch1 multiple copy number (51% (73/146)) were observed on the Thailand-Myanmar border compared to other parts of Thailand. Overall, the prevalence of septuple mutations was observed for pfdhfr-pfdhps haplotypes. In particular, the prevalence of pfdhfr-pfdhps, septuple mutation was observed in the Thailand-Myanmar (50%, 73/146) and Thailand-Cambodia (65%, 26/40) border. In Thailand-Malaysia border, majority of the pfdhfr-pfdhps haplotypes transaction from quadruple (90%, 9/10) to quintuple (65%, 24/37) during 2008-2016. Within the pfdhfr-pfdhps haplotypes, during 2008-2013 the pfdhps A/S436F mutation was observed only in Thailand-Myanmar border (9%, 10/107), while it was not identified later. In general, significant correlation was observed between the prevalence of pfdhfr I164L (ϕ = 0.213, p-value = 0.001) or pfdhps K540E/N (ϕ = 0.399, p-value ≤ 0.001) mutations and pfgch1 gene amplification.
CONCLUSIONS: Despite withdrawal of SP as anti-malarial treatment for 17 years, the border regions of Thailand continue to display high prevalence of antifolate and anti-sulfonamide resistance markers in falciparum malaria. Significant association between pfgch1 amplification and pfdhfr (I164L) or pfdhps (K540E) resistance markers were observed, suggesting a compensatory mutation.
METHODS: We carried out a systematic search in 11 electronic databases to identify in vivo studies published between 2001 and 2017 that reported artemisinin resistance. This was then followed by A network meta-analysis to compare the efficacy of different ACTs. Quality assessment was performed using the Cochrane Risk of Bias (ROB) tool for randomized controlled trials and National Institute of Health (NIH) tool for cross-sectional studies. The study protocol was registered in PROSPERO under number CRD42018087574.
RESULTS: With 8400 studies initially identified, 82 were eligible for qualitative and quantitative analysis. Artemisinin resistance was only reported in South East Asia. K13 mutation C580Y was the most abundant mutation associated with resistance having an abundance of 63.1% among all K13 mutations reported. Although the overall network meta-analysis had shown good performance of dihydroartemisinin piperaquine in the early years, a subgroup analysis of the recent years revealed a poor performance of the drug in relation to recrudescence, clinical failure and parasitological failure especially in the artemisinin resistant regions.
CONCLUSION: With report of high resistance and treatment failure against the leading artemisinin combination therapy in South East Asia, it is imperative that a new drug or a formulation is developed before further spread of resistance.