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Host immunity to Plasmodium falciparum and the assessment of emerging artemisinin resistance in a multinational cohort.

ABSTRACT: Artemisinin-resistant falciparum malaria, defined by a slow-clearance phenotype and the presence of kelch13 mutants, has emerged in the Greater Mekong Subregion. Naturally acquired immunity to malaria clears parasites independent of antimalarial drugs. We hypothesized that between- and within-population variations in host immunity influence parasite clearance after artemisinin treatment and the interpretation of emerging artemisinin resistance. Antibodies specific to 12 Plasmodium falciparum sporozoite and blood-stage antigens were determined in 959 patients (from 11 sites in Southeast Asia) participating in a multinational cohort study assessing parasite clearance half-life (PCt_1/2) after artesunate treatment and kelch13 mutations. Linear mixed-effects modeling of pooled individual patient data assessed the association between antibody responses and PCt_1/2.P. falciparum antibodies were lowest in areas where the prevalence of kelch13 mutations and slow PCt_1/2 were highest [Spearman ? = -0.90 (95% confidence interval, -0.97, -0.65), and Spearman ? = -0.94 (95% confidence interval, -0.98, -0.77), respectively]. P. falciparum antibodies were associated with faster PCt_1/2 (mean difference in PCt_1/2 according to seropositivity, -0.16 to -0.65 h, depending on antigen); antibodies have a greater effect on the clearance of kelch13 mutant compared with wild-type parasites (mean difference in PCt_1/2 according to seropositivity, -0.22 to -0.61 h faster in kelch13 mutants compared with wild-type parasites). Naturally acquired immunity accelerates the clearance of artemisinin-resistant parasites in patients with falciparum malaria and may confound the current working definition of artemisinin resistance. Immunity may also play an important role in the emergence and transmission potential of artemisinin-resistant parasites.

SUBMITTER: Ataide R

PROVIDER: S-EPMC5380044 | biostudies-literature | 2017 Mar

REPOSITORIES: biostudies-literature

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Host immunity to Plasmodium falciparum and the assessment of emerging artemisinin resistance in a multinational cohort.

Ataide Ricardo R Ashley Elizabeth A EA Powell Rosanna R Chan Jo-Anne JA Malloy Michael J MJ O'Flaherty Katherine K Takashima Eizo E Langer Christine C Tsuboi Takafumi T Dondorp Arjen M AM Day Nicholas P NP Dhorda Mehul M Fairhurst Rick M RM Lim Pharath P Amaratunga Chanaki C Pukrittayakamee Sasithon S Hien Tran Tinh TT Htut Ye Y Mayxay Mayfong M Faiz M Abul MA Beeson James G JG Nosten Francois F Simpson Julie A JA White Nicholas J NJ Fowkes Freya J I FJ

Proceedings of the National Academy of Sciences of the United States of America 20170313 13

Artemisinin-resistant falciparum malaria, defined by a slow-clearance phenotype and the presence of kelch13 mutants, has emerged in the Greater Mekong Subregion. Naturally acquired immunity to malaria clears parasites independent of antimalarial drugs. We hypothesized that between- and within-population variations in host immunity influence parasite clearance after artemisinin treatment and the interpretation of emerging artemisinin resistance. Antibodies specific to 12 Plasmodium falc ...[more]

PMID: 28289193

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Project description:BackgroundArtemisinin-based combination therapies are the recommended first-line treatments of falciparum malaria in all countries with endemic disease. There are recent concerns that the efficacy of such therapies has declined on the Thai-Cambodian border, historically a site of emerging antimalarial-drug resistance.MethodsIn two open-label, randomized trials, we compared the efficacies of two treatments for uncomplicated falciparum malaria in Pailin, western Cambodia, and Wang Pha, northwestern Thailand: oral artesunate given at a dose of 2 mg per kilogram of body weight per day, for 7 days, and artesunate given at a dose of 4 mg per kilogram per day, for 3 days, followed by mefloquine at two doses totaling 25 mg per kilogram. We assessed in vitro and in vivo Plasmodium falciparum susceptibility, artesunate pharmacokinetics, and molecular markers of resistance.ResultsWe studied 40 patients in each of the two locations. The overall median parasite clearance times were 84 hours (interquartile range, 60 to 96) in Pailin and 48 hours (interquartile range, 36 to 66) in Wang Pha (P<0.001). Recrudescence confirmed by means of polymerase-chain-reaction assay occurred in 6 of 20 patients (30%) receiving artesunate monotherapy and 1 of 20 (5%) receiving artesunate-mefloquine therapy in Pailin, as compared with 2 of 20 (10%) and 1 of 20 (5%), respectively, in Wang Pha (P=0.31). These markedly different parasitologic responses were not explained by differences in age, artesunate or dihydroartemisinin pharmacokinetics, results of isotopic in vitro sensitivity tests, or putative molecular correlates of P. falciparum drug resistance (mutations or amplifications of the gene encoding a multidrug resistance protein [PfMDR1] or mutations in the gene encoding sarco-endoplasmic reticulum calcium ATPase6 [PfSERCA]). Adverse events were mild and did not differ significantly between the two treatment groups.ConclusionsP. falciparum has reduced in vivo susceptibility to artesunate in western Cambodia as compared with northwestern Thailand. Resistance is characterized by slow parasite clearance in vivo without corresponding reductions on conventional in vitro susceptibility testing. Containment measures are urgently needed. (ClinicalTrials.gov number, NCT00493363, and Current Controlled Trials number, ISRCTN64835265.)

Project description:BackgroundArtemisinin resistance in Plasmodium falciparum has emerged in Southeast Asia and now poses a threat to the control and elimination of malaria. Mapping the geographic extent of resistance is essential for planning containment and elimination strategies.MethodsBetween May 2011 and April 2013, we enrolled 1241 adults and children with acute, uncomplicated falciparum malaria in an open-label trial at 15 sites in 10 countries (7 in Asia and 3 in Africa). Patients received artesunate, administered orally at a daily dose of either 2 mg per kilogram of body weight per day or 4 mg per kilogram, for 3 days, followed by a standard 3-day course of artemisinin-based combination therapy. Parasite counts in peripheral-blood samples were measured every 6 hours, and the parasite clearance half-lives were determined.ResultsThe median parasite clearance half-lives ranged from 1.9 hours in the Democratic Republic of Congo to 7.0 hours at the Thailand-Cambodia border. Slowly clearing infections (parasite clearance half-life >5 hours), strongly associated with single point mutations in the "propeller" region of the P. falciparum kelch protein gene on chromosome 13 (kelch13), were detected throughout mainland Southeast Asia from southern Vietnam to central Myanmar. The incidence of pretreatment and post-treatment gametocytemia was higher among patients with slow parasite clearance, suggesting greater potential for transmission. In western Cambodia, where artemisinin-based combination therapies are failing, the 6-day course of antimalarial therapy was associated with a cure rate of 97.7% (95% confidence interval, 90.9 to 99.4) at 42 days.ConclusionsArtemisinin resistance to P. falciparum, which is now prevalent across mainland Southeast Asia, is associated with mutations in kelch13. Prolonged courses of artemisinin-based combination therapies are currently efficacious in areas where standard 3-day treatments are failing. (Funded by the U.K. Department of International Development and others; ClinicalTrials.gov number, NCT01350856.).

Project description:BACKGROUND: Artemisinin-based combination therapy (ACT) is the mainstay of global efforts for treatment of Plasmodium falciparum malaria, but decline in its efficacy is the most important obstacle towards malaria control and elimination. Therefore, the present molecular analysis provides information on putative mutations associated with artemisinin resistance in P. falciparum clinical population unexposed and exposed to artesunate 4 years after adoption of ACT as the first-line anti-malarial therapy in Iran. METHODS: In this study, blood samples (n = 226) were collected from uncomplicated P. falciparum-infected patients from different health centers of Chabahar district in Sistan and Baluchistan province in the south-eastern part of Iran, during 2003 to 2010. All collected isolates were analysed for putative candidate mutations (TTA) L263E (GAA), (GAA) E431K (AAA), (GCA) A623E (GAA) and (AGT) S769N (AAT) of pfatpase6 gene using nested PCR/RFLP, followed by sequencing. Furthermore, the gene copy number was assessed by real-time quantitative PCR (RT-qPCR) in the presence of SYBR green. RESULTS: Neither the pfatpase6 L263E nor the A623E mutation was detected among all examined isolates. The E431K mutation was found in 23% of the analysed samples unexposed to ACT; however, it was detected in 17.8% (34/191) of P. falciparum isolates exposed to artesunate after 2007. High frequency of this single nucleotide polymorphisms (SNP) (overall 18.6%) among both examined groups (X2 test, P>0.05) indicated that this SNP should be considered as an unrelated mutation to artemisinin resistance. In contrast, S769N mutation was not detected in unexposed isolates; however, it was found in 2.6% (5/191), four years after introduction of ACT in this malaria setting. Also, detected SNPs were not significantly frequent in both unexposed and exposed examined isolates (X2 test, P> 0.05). Investigation in the copy number of pfatpase6 gene revealed a similar number of copy (n = 1) as in an isolate sensitive to artemisinin. CONCLUSION: Taken together, the results suggest, in particular, that pfatpase6 S769N gene needs more consideration for its possible association with artesunate resistance among P. falciparum isolates.

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Host immunity to Plasmodium falciparum and the assessment of emerging artemisinin resistance in a multinational cohort.

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Host immunity to <i>Plasmodium falciparum</i> and the assessment of emerging artemisinin resistance in a multinational cohort.

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