High prevalence of Plasmodium falciparum antimalarial drug resistance markers in isolates from asymptomatic patients from the Republic of the Congo between 2010 and 2015

What exactly does the PfK13 C580Y mutation in Plasmodium falciparum influence?

BACKGROUND

The emergence and spread of artemisinin resistance threaten global malaria control and elimination goals, and encourage research on the mechanisms of drug resistance in malaria parasites. Mutations in Plasmodium falciparum Kelch 13 (PfK13) protein are associated with artemisinin resistance, but the unique or common mechanism which results in this resistance is unclear.

METHODS

We analyzed the effects of the PfK13 mutation on the transcriptome and proteome of P. falciparum at different developmental stages. Additionally, the number of merozoites, hemozoin amount, and growth of P. falciparum 3D7C580Y and P. falciparum 3D7WT were compared. The impact of iron supplementation on the number of merozoites of P. falciparum 3D7C580Y was also examined.

RESULTS

We found that the PfK13 mutation did not significantly change glycolysis, TCA, pentose phosphate pathway, or oxidative phosphorylation, but did reduce the expression of reproduction- and DNA synthesis-related genes. The reduced number of merozoites, decreased level of hemozoin, and slowed growth of P. falciparum 3D7C580Y were consistent with these changes. Furthermore, adding iron supply could increase the number of the merozoites of P. falciparum 3D7C580Y.

CONCLUSIONS

These results revealed that the PfK13 mutation reduced hemoglobin ingestion, leading to artemisinin resistance, likely by decreasing the parasites' requirement for haem and iron. This study helps elucidate the mechanism of artemisinin resistance due to PfK13 mutations.

Prevalence of malaria among febrile patients and assessment of efficacy of artemether-lumefantrine and artesunate-amodiaquine for uncomplicated malaria in Dolisie, Republic of the Congo

BACKGROUND

In the Republic of the Congo, malaria represents a major public health problem affecting all age groups. A regular surveillance of the current efficacy of first-line anti-malarial drugs is required in the face of possible emergence and spread of artemisinin-resistant Plasmodium falciparum strains in Africa. The purpose of this study was to determine the prevalence of malaria among febrile patients of all ages and assess the efficacy of artemether-lumefantrine (AL) and artesunate-amodiaquine (ASAQ) in Congolese children.

METHODS

Febrile patients of all ages were initially screened for malaria by both rapid diagnostic test (RDT) and microscopy. Patients less than 12 years of age, with parasitaemia ≥ 1000 asexual parasites of P. falciparum/µL of blood, without any signs of severity, were enrolled in a therapeutic efficacy study and treated after obtaining their parents' (or legal guardian's) informed consent in two health centres in Dolisie. The patients were followed for 28 days in accordance with the 2009 World Health Organization standard protocol. If parasitaemia reappeared on or after day 7, the genetic profiles (genes expressing merozoite surface protein-1 [msp1], merozoite surface protein-2 [msp2], and glutamine-rich protein [glurp]) of pre-treatment and post-treatment isolates were compared by nested polymerase chain reaction (PCR) followed by capillary electrophoresis to make a distinction between recrudescence and re-infection. The clinical and parasitological outcome was analysed by the per-protocol method and Kaplan-Meier survival curves.

RESULTS

A total of 994 febrile patients of all ages were screened by RDT and microscopy. Of 994 patients, 323 (32.5%) presented a positive RDT, and 266 (26.8%) were microscopy-positive. Based on microscopy as the reference diagnostic method, the sensitivity and the specificity of the RDT were 98.9 and 91.8%, respectively. The Cohen's kappa coefficient was 0.86. A total of 121 children aged less than 12 years (61 in AL treatment group and 60 in ASAQ treatment group) were included in therapeutic efficacy study. Before PCR correction, the proportions of adequate clinical and parasitological response were 96.6% for AL and 86.0% for ASAQ in the per-protocol population (P < 0.05). The PCR-corrected efficacy rates were 98.2% and 94.2% for AL and ASAQ, respectively (P > 0.05). Both treatments were well tolerated.

CONCLUSIONS

AL and ASAQ remain highly effective for the first-line treatment of uncomplicated P. falciparum malaria in Dolisie. Despite high efficacy of first- and second-line treatment, there is a continuing need to scale up effective malaria preventive interventions and vector control strategies in the country.

TRIAL REGISTRATION NUMBER

ACTRN12616001422415.

Role of Anopheles stephensi Mosquitoes in Malaria Outbreak, Djibouti, 2019

Anopheles stephensi mosquitoes share urban breeding sites with Aedes aegypti and Culex quinquefasciatus mosquitoes in the Republic of Djibouti. We present evidence that A. stephensi mosquitoes might be responsible for an increase in malaria incidence in this country. We also document resistance of Plasmodium falciparum to dihydroartemisinin/piperaquine.

Geographical spread and structural basis of sulfadoxine-pyrimethamine drug-resistant malaria parasites

The global spread of sulfadoxine (Sdx, S) and pyrimethamine (Pyr, P) resistance is attributed to increasing number of mutations in DHPS and DHFR enzymes encoded by malaria parasites. The association between drug resistance mutations and SP efficacy is complex. Here we provide an overview of the geographical spread of SP resistance mutations in Plasmodium falciparum (Pf) and Plasmodium vivax (Pv) encoded dhps and dhfr genes. In addition, we have collated the mutation data and mapped it on to the three-dimensional structures of DHPS and DHFR which have become available. Data from genomic databases and 286 studies were collated to provide a comprehensive landscape of mutational data from 2005 to 2019. Our analyses show that the Pyr-resistant double mutations are widespread in Pf/PvDHFR (P. falciparum ∼61% in Asia and the Middle East, and in the Indian sub-continent; in P. vivax ∼33% globally) with triple mutations prevailing in Africa (∼66%) and South America (∼33%). For PfDHPS, triple mutations dominate South America (∼44%), Asia and the Middle East (∼34%) and the Indian sub-continent (∼27%), while single mutations are widespread in Africa (∼45%). Contrary to the status for P. falciparum, Sdx-resistant single point mutations in PvDHPS dominate globally. Alarmingly, highly resistant quintuple and sextuple mutations are rising in Africa (PfDHFR-DHPS) and Asia (Pf/PvDHFR-DHPS). Structural analyses of DHFR and DHPS proteins in complexes with substrates/drugs have revealed that resistance mutations map proximal to Sdx and Pyr binding sites. Thus new studies can focus on discovery of novel inhibitors that target the non-substrate binding grooves in these two validated malaria parasite drug targets.

Spatial and molecular mapping of Pfkelch13 gene polymorphism in Africa in the era of emerging Plasmodium falciparum resistance to artemisinin: a systematic review

The spread of Plasmodium falciparum isolates carrying mutations in the kelch13 (Pfkelch13) gene associated with artemisinin resistance (PfART-R) in southeast Asia threatens malaria control and elimination efforts. Emergence of PfART-R in Africa would result in a major public health problem. In this systematic review, we investigate the frequency and spatial distribution of Pfkelch13 mutants in Africa, including mutants linked to PfART-R in southeast Asia. Seven databases were searched (PubMed, Embase, Scopus, African Journal Online, African Index Medicus, Bioline, and Web of Science) for relevant articles about polymorphisms of the Pfkelch13 gene in Africa before January, 2019. Following PRISMA guidelines, 53 studies that sequenced the Pfkelch13 gene of 23 100 sample isolates in 41 sub-Saharan African countries were included. The Pfkelch13 sequence was highly polymorphic (292 alleles, including 255 in the Pfkelch13-propeller domain) but with mutations occurring at very low relative frequencies. Non-synonymous mutations were found in only 626 isolates (2·7%) from west, central, and east Africa. According to WHO, nine different mutations linked to PfART-R in southeast Asia (Phe446Ile, Cys469Tyr, Met476Ile, Arg515Lys, Ser522Cys, Pro553Leu, Val568Gly, Pro574Leu, and Ala675Val) were detected, mainly in east Africa. Several other Pfkelch13 mutations, such as those structurally similar to southeast Asia PfART-R mutations, were also identified, but their relevance for drug resistance is still unknown. This systematic review shows that Africa, thought to not have established PfART-R, reported resistance-related mutants in the past 5 years. Surveillance using PfART-R molecular markers can provide valuable decision-making information to sustain the effectiveness of artemisinin in Africa.