Susceptibility of Plasmodium falciparum to artemisinins and Plasmodium vivax to chloroquine in Phuoc Chien Commune, Ninh Thuan Province, south-central Vietnam

Magnitude and patterns of severe Plasmodium vivax monoinfection in Vietnam: a 4-year single-center retrospective study

Introduction

Infection with Plasmodium vivax is a recognized cause of severe malaria including deaths. The exact burden and patterns of severe P. vivax monoinfections is however still not well quantified, especially in P. vivax endemic regions. We examined the magnitude and patterns of severe malaria caused by monoinfections of P. vivax and associated predictors among patients admitted to a tertiary care center for malaria in Vietnam.

Methods

A retrospective cohort study was conducted based on the patients' medical records at the Hospital for Tropical Diseases from January 2015 to December 2018. Extracted information included demographic, epidemiologic, clinical, laboratory and treatment characteristics.

Results

Monoinfections with P. vivax were found in 153 (34.5, 95% CI 30.3-39.1%) patients of whom, uncomplicated and severe malaria were documented in 89.5% (137/153, 95% CI 83.7-93.5%) and 10.5% (16/153, 95% CI 6.5-16.3%), respectively. Patterns of severe malaria included jaundice (8 cases), hypoglycemia (3 cases), shock (2 cases), anemia (2 cases), and cerebral malaria (1 case). Among 153 patients, 73 (47.7%) had classic malaria paroxysm, 57 (37.3%) had >7 days of illness at the time of admission, and 40 (26.1%) were referred from other hospitals. A misdiagnosis as having other diseases from malaria cases coming from other hospitals was up to 32.5% (13/40). Being admitted to hospital after day 7th of illness (AOR = 6.33, 95% CI 1.14-35.30, p = 0.035) was a predictor of severe malaria. Severe malaria was statistically associated with longer hospital length of stay (p = 0.035). Early and late treatment failures and recrudescence were not recorded. All patients recovered completely.

Discussion

This study confirms the emergence of severe vivax malaria in Vietnam which is associated with delayed hospital admission and increased hospital length of stay. Clinical manifestations of P. vivax infection can be misdiagnosed which results in delayed treatment. To meet the goal of malaria elimination by 2030, it is crucial that the non-tertiary hospitals have the capacity to quickly and correctly diagnose malaria and then provide treatment for malaria including P. vivax infections. More robust studies need to be conducted to fully elucidate the magnitude of severe P. vivax in Vietnam.

A single point mutation in the Plasmodium falciparum 3'-5' exonuclease does not alter piperaquine susceptibility

Background

The rise in Plasmodium falciparum resistance to dihydroartemisinin–piperaquine (DHA–PPQ) treatment has been documented in the Greater Mekong Subregion with associations with mutations in the P. falciparum chloroquine resistance transporter (pfcrt) and plasmepsin 2 (pfpm2) genes. However, it is unclear whether other genes also play a role with PPQ resistance, such as the E415G mutation in the exonuclease (pfexo) gene. The aim of this study was to investigate the role of this mutation in PPQ resistance by generating transgenic parasites expressing the pfexo-E415G mutant allele.

Methods

Transgenic parasite clones carrying the E415G mutation in PfEXO of the B5 isolate were derived by CRISPR-Cas9 gene editing and verified using PCR and gene sequencing. Polymorphisms of pfkelch-13, pfcrt, and pfexo were examined by PCR while the copy number variations of pfpm2 were examined by both relative quantitative real-time PCR and the duplication breakpoint assay. Drug sensitivity against a panel of antimalarials, the ring-stage survival assay (RSA), the PPQ survival assay (PSA), and bimodal dose-response curves were used to evaluate antimalarial susceptibility.

Results

The transgenic line, B5-rexo-E415G-B8, was successfully generated. The PPQ-IC₉₀, %PPQ survival, and the bimodal dose-response clearly showed that E415G mutation in PfEXO of B5 isolate remained fully susceptible to PPQ. Furthermore, growth assays demonstrated that the engineered parasites grew slightly faster than the unmodified parental isolates whereas P. falciparum isolates harbouring pfkelch-13, pfcrt, and pfexo mutations with multiple copies of pfpm2 grew much more slowly.

Conclusions

Insertion of the E415G mutation in PfEXO did not lead to increased PPQ-IC₉₀ and %PPQ survival, suggesting that this mutation alone may not be associated with PPQ resistance, but could still be an important marker if used in conjunction with other markers for monitoring PPQ-resistant parasites. The results also highlight the importance of monitoring and evaluating suspected genetic mutations with regard to parasite fitness and resistance.

Supplementary information

The online version contains supplementary material available at 10.1186/s12936-022-04148-z.

Pyronaridine-Artesunate (Pyramax) for Treatment of Artemisinin- and Piperaquine-Resistant Plasmodium falciparum in the Central Highlands of Vietnam

The rise in Plasmodium falciparum resistance to dihydroartemisinin-piperaquine in Vietnam justifies the need to evaluate alternative artemisinin-based combination therapies. Between July 2018 and October 2019, a single-arm trial of pyronaridine-artesunate (Pyramax, PA) was conducted in Dak Nong province, Vietnam. PA (3-day course) was administered to adults and children infected with P. falciparum. PA was well tolerated by the participants. The proportion of patients with Day 42 PCR-corrected adequate clinical and parasitological response was 95.2% (95% confidence interval [CI], 82.3 to 98.8, n = 40/42) for treating falciparum malaria. The median parasite clearance half-life was 6.7 h (range, 2.6 to 11.9) and the median parasite clearance time was 72 h (range, 12 to 132) with 44.9% (22/49) of patients having positive blood films at 72 h. The two patients that recrudesced had comparable Day 7 blood pyronaridine concentrations (39.5 and 39.0 ng/ml) to the 40 patients who did not recrudesce (median 43.4 ng/ml, 95% CI, 35.1 to 54.9). Ring-stage and piperaquine survival assays revealed that of the 29 P. falciparum isolates collected from the patients before PA treatment, 22 (75.9%) had reduced susceptibility to artemisinins and 17 (58.6%) were resistant to piperaquine. Genotyping confirmed that 92.0% (46/50) of falciparum patients were infected with parasites bearing the Pfkelch13 C580Y mutation associated with artemisinin resistance. Of these, 56.0% (28/50) of the isolates also had multiple copies of the plasmepsin 2/3 genes responsible for piperaquine resistance. Overall, PA was effective in treating P. falciparum in the Central Highlands of Vietnam. (This study has been registered at AustralianClinicalTrials.gov.au under trial ID ACTRN12618001429246.).

Adenine Modification at C7 as a Viable Strategy to Potentiate the Antimalarial Activity of Quinolones

Although many quinolones have shown promise as potent antimalarials, their clinical development has been slow due to poor performance in vivo. Insights into structural modifications that can improve their therapeutic potential will be very valuable in this vibrant area of research. Our studies involving a library of quinolones which vary in substitution pattern at N1, C3, C6 and C7 positions have shown that the presence of adenine moiety at C7 can bring a noticeable improvement in activity compared to other heterocyclic groups at this location. The most potent compound emerged from this study showed IC₅₀ values of 0.38 μM and 0.75 μM against chloroquine-sensitive and -resistant (W2) strains, respectively. Docking analysis in the Q_o site of cytochrome bc1 complex revealed the contribution of a key H-bonding interaction from the adenine unit in target binding. This corroborates with compound-induced loss of mitochondrial functions. These findings not only open avenues for further exploration of antimalarial potential of adenine-modified quinolones, but also suggests broader opportunities during lead-optimization against other antimalarial targets.

High Proportion of Genome-Wide Homology and Increased Pretreatment pvcrt Levels in Plasmodium vivax Late Recurrences: a Chloroquine Therapeutic Efficacy Study

Chloroquine (CQ) is the first-line treatment for Plasmodium vivax malaria in most countries where malaria is endemic. Monitoring P. vivax CQ resistance (CQR) is critical but remains challenged by the difficulty to distinguish real treatment failure from reinfection or liver relapse. The therapeutic efficacy of CQ against uncomplicated P. vivax malaria was evaluated in Gia Lai Province, Vietnam. Sixty-seven patients were enrolled and followed for 42 days using microscopy and quantitative PCR. Adequate clinical and parasitological response (ACPR) was 100% (66/66) on day 28 but 75.4% (49/65) on day 42. Eighteen recurrences (27.7%) were detected, with a median time to recurrence of 42 days (interquartile range [IQR], 35 to 42) and blood CQ concentration of <100 ng/ml. Primary infections leading to recurrence occurred in younger individuals (median age for ACPR = 25 years [IQR, 20 to 28]; recurrences = 18 [16 to 21]; P = 0.002) had a longer parasite clearance time (PCT for ACPR = 47.5 h [IQR, 36.2 to 59.8 h]; recurrences = 54.2 [48.4 to 62.0]; P = 0.035) and higher pvcrt gene expression (median relative expression ratio for ACPR = 0.09 [IQR, 0.05 to 0.22]; recurrences = 0.20 [0.15 to 0.56]; P = 0.002), but showed no differences in ex vivo CQ sensitivity. Parasite genotyping by microsatellites, single nucleotide polymorphism (SNP) barcoding, and whole-genome sequencing (WGS) identified a majority of homologous recurrences, with 80% (8/10) showing >98% identity by descent to paired day 0 samples. This study shows that CQ remained largely efficacious to treat P. vivax in Gia Lai; i.e., recurrences occurred late (>day 28) and in the presence of low blood CQ concentrations. However, the combination of both WGS and gene expression analysis (pvcrt) data with clinical data (PCT) allowed us to identify potential emergence of low-grade CQR, which should be closely monitored. (This study has been registered at ClinicalTrials.gov under identifier NCT02610686.).

Efficacy of dihydroartemisinin/piperaquine and artesunate monotherapy for the treatment of uncomplicated Plasmodium falciparum malaria in Central Vietnam

BACKGROUND

Artemisinin-based combination therapies (ACTs) have significantly contributed to reduce Plasmodium falciparum malaria burden in Vietnam, but their efficacy is challenged by treatment failure of dihydroartemisinin/piperaquine ACT in Southern provinces.

OBJECTIVES

To assess the efficacy of dihydroartemisinin/piperaquine for uncomplicated P. falciparum malaria in Gia Lai, Central Vietnam, and determine parasite resistance to artemisinin (ClinicalTrials.gov identifier NCT02604966).

METHODS

Sixty patients received either dihydroartemisinin/piperaquine (4 mg/kg/day, 3 days; n = 33) or artesunate monotherapy (4 mg/kg/day, 3 days; n = 27) followed by dihydroartemisinin/piperaquine (AS + DHA/PPQ). Clinical phenotypes were determined during a 42 day follow-up and analysed together with ex vivo susceptibility to antimalarials and molecular markers of drug resistance.

RESULTS

Day 3 positivity rate was significantly higher in the AS + DHA/PPQ arm compared with dihydroartemisinin/piperaquine (70.4% versus 39.4%, P = 0.016). Parasite clearance time was 95.2 h (AS + DHA/PPQ) versus 71.9 h (dihydroartemisinin/piperaquine, P = 0.063) and parasite clearance half-life was 7.4 h (AS + DHA/PPQ) versus 7.0 h (dihydroartemisinin/piperaquine, P = 0.140). Adequate clinical and parasitological response at Day 42 was 100% in both arms. By RT-qPCR, 36% (19/53) patients remained positive until Day 7. No recurrences were detected. kelch13 artemisinin resistance mutations were found in 87% (39/45) of isolates and 50% (20/40) were KEL1/C580Y. The piperaquine resistance marker plasmepsin-2 was duplicated in 10.4% (5/48). Isolates from Day 3-positive patients (n = 18) had higher ex vivo survival rates to artemisinin compounds (P < 0.048) and prevalence of kelch13 mutations (P = 0.005) than Day 3-negative patients (n = 5). The WHO definition of artemisinin resistance was fulfilled in 60% (24/40) of cases.

CONCLUSIONS

Although dihydroartemisinin/piperaquine remained effective to treat P. falciparum, the high Day 3 positivity rate and prevalence of KEL1 strains calls for continuous monitoring of dihydroartemisinin/piperaquine efficacy in Central Vietnam.

Progress and challenges in the use of fluorescence-based flow cytometric assays for anti-malarial drug susceptibility tests

Drug-resistant Plasmodium is a frequent global threat in malaria eradication programmes, highlighting the need for new anti-malarial drugs and efficient detection of treatment failure. Plasmodium falciparum culture is essential in drug discovery and resistance surveillance. Microscopy of Giemsa-stained erythrocytes is common for determining anti-malarial effects on the intraerythrocytic development of cultured Plasmodium parasites. Giemsa-based microscopy use is conventional but laborious, and its accuracy depends largely on examiner skill. Given the availability of nucleic acid-binding fluorescent dyes and advances in flow cytometry, the use of various fluorochromes has been frequently attempted for the enumeration of parasitaemia and discrimination of P. falciparum growth in drug susceptibility assays. However, fluorochromes do not meet the requirements of being fast, simple, reliable and sensitive. Thus, this review revisits the utility of fluorochromes, notes previously reported hindrances, and highlights the challenges and opportunities for using fluorochromes in flow cytometer-based drug susceptibility tests. It aims to improve drug discovery and support a resistance surveillance system, an essential feature in combatting malaria.

Molecular surveillance and temporal monitoring of malaria parasites in focal Vietnamese provinces

BACKGROUND

While the World Health Organization (WHO) Southeast Asia region has the second highest incidence of malaria worldwide, malaria in Vietnam is focal to few provinces, where delayed parasite clearance to anti-malarial drugs is documented. This study aims to understand Plasmodium species distribution and the genetic diversity of msp1 and msp2 of parasite populations using molecular tools.

METHODS

A total of 222 clinical isolates from individuals with uncomplicated malaria were subjected to Plasmodium species identification by nested real-time PCR. 166 isolates positive for Plasmodium falciparum mono infections were further genotyped for msp1 (MAD20, K1, and RO33), and msp2 allelic families (3D7 and FC27). Amplicons were resolved through capillary electrophoresis in the QIAxcel Advanced system.

RESULTS

Mono-infections were high and with 75% P. falciparum, 14% Plasmodium vivax and 9% P. falciparum/P. vivax co-infections, with less than 1% Plasmodium malariae identified. For msp1, MAD20 was the most prevalent (99%), followed by K1 (46%) allelic family, with no sample testing positive for RO33 (0%). For msp2, 3D7 allelic family was predominant (97%), followed by FC27 (10%). The multiplicity of infection of msp1 and msp2 was 2.6 and 1.1, respectively, and the mean overall multiplicity of infection was 3.7, with the total number of alleles ranging from 1 to 7.

CONCLUSIONS

Given the increasing importance of antimalarial drugs in the region, the genetic diversity of P. falciparum msp1 and msp2 should be regularly monitored with respect to treatment outcomes and/or efficacy studies in regions, where there are ongoing changes in the malaria epidemiology.

An insight into the recent development of the clinical candidates for the treatment of malaria and their target proteins

Malaria is an endemic disease, prevalent in tropical and subtropical regions which cost half of million deaths annually. The eradication of malaria is one of the global health priority nevertheless, current therapeutic efforts seem to be insufficient due to the emergence of drug resistance towards most of the available drugs, even first-line treatment ACT, unavailability of the vaccine, and lack of drugs with a new mechanism of action. Intensification of antimalarial research in recent years has resulted into the development of single dose multistage therapeutic agents which has advantage of overcoming the antimalarial drug resistance. The present review explored the current progress in the development of new promising antimalarials against prominent target proteins that have the potential to be a clinical candidate. Here, we also reviewed different aspects of drug resistance and highlighted new drug candidates that are currently in a clinical trial or clinical development, along with a few other molecules with excellent antimalarial activity overs ACTs. The summarized scientific value of previous approaches and structural features of antimalarials related to the activity are highlighted that will be helpful for the development of next-generation antimalarials.