Heterogeneous distribution of k13 mutations in Plasmodium falciparum in Laos

Antimalarial Mechanisms and Resistance Status of Artemisinin and Its Derivatives

Artemisinin is an endoperoxide sesquiterpene lactone isolated from Artemisia annua and is often used to treat malaria. Artemisinin's peroxide bridge is the key structure behind its antimalarial action. Scientists have created dihydroartemisinin, artemether, artesunate, and other derivatives preserving artemisinin's peroxide bridge to increase its clinical utility value. Artemisinin compounds exhibit excellent efficacy, quick action, and minimal toxicity in malaria treatment and have greatly contributed to malaria control. With the wide and unreasonable application of artemisinin-based medicines, malaria parasites have developed artemisinin resistance, making malaria prevention and control increasingly challenging. Artemisinin-resistant Plasmodium strains have been found in many countries and regions. The mechanisms of antimalarials and artemisinin resistance are not well understood, making malaria prevention and control a serious challenge. Understanding the antimalarial and resistance mechanisms of artemisinin drugs helps develop novel antimalarials and guides the rational application of antimalarials to avoid the spread of resistance, which is conducive to malaria control and elimination efforts. This review will discuss the antimalarial mechanisms and resistance status of artemisinin and its derivatives, which will provide a reference for avoiding drug resistance and the research and development of new antimalarial drugs.

Performance of the procedure for ultra-rapid extraction and loop-mediated isothermal amplification (PURE-LAMP) method to detect malaria in Haiti

BACKGROUND

Malaria continues to cause burden in various parts of the world. Haiti, a Caribbean country, is among those aiming to eliminate malaria within a few years. Two surveys were conducted in Haiti during which we aimed to evaluate the performance of the simple and rapid procedure for ultra-rapid extraction-loop-mediated isothermal amplification (PURE-LAMP) method with dried blood spots as an alternative diagnostic method for malaria in the context of low to very low rates of transmission.

METHODS

Febrile and afebrile people were recruited from three administrative divisions within Haiti: Nippes, Sud and Grand'Anse, during the summers of 2017 (early August to early September) and 2018 (late July to late August). Their blood samples were tested by microscopy, rapid diagnostic tests (RDT), PURE-LAMP and nested PCR to detect Plasmodium infection. Sensitivity, specificity, positive and negative predictive values and kappa statistics were estimated with the nested PCR results as the gold standard.

RESULTS

Among 1074 samples analyzed, a positive rate of 8.3% was calculated based on the nested PCR results. Among febrile participants, the rates in 2017 and 2018 were 14.6% and 1.4%, respectively. Three positives were detected among 172 afebrile participants in 2018 by PURE-LAMP and nested PCR, and all three were from the same locality. There was no afebrile participants recruited in 2017. The PURE-LAMP, RDT and microscopy had respective sensitivities of 100%, 85.4% and 49.4%. All of the testing methods had specificities over 99%.

CONCLUSIONS

This study confirmed the high performance of the PURE-LAMP method to detect Plasmodium infection with dried blood spots and recommends its use in targeted mass screening and treatment activities in low endemic areas of malaria.

Molecular surveillance of artemisinin resistance-related Pfk13 and pfcrt polymorphisms in imported Plasmodium falciparum isolates reported in eastern China from 2015 to 2019

BACKGROUND

Artemisinin-based combination therapy (ACT) has been recommended as the first-line treatment by the World Health Organization to treat uncomplicated Plasmodium falciparum malaria. However, the emergence and spread of P. falciparum resistant to artemisinins and their partner drugs is a significant risk for the global effort to reduce disease burden facing the world. Currently, dihydroartemisinin-piperaquine (DHA-PPQ) is the most common drug used to treat P. falciparum, but little evidence about the resistance status targeting DHA (ACT drug) and its partner drug (PPQ) has been reported in Shandong Province, China.

METHODS

A retrospective study was conducted to explore the prevalence and spatial distribution of Pfk13 and Pfcrt polymorphisms (sites of 72-76, and 93-356) among imported P. falciparum isolates between years 2015-2019 in Shandong Province in eastern China. Individual epidemiological information was collected from a web-based reporting system were reviewed and analysed.

RESULTS

A total of 425 P. falciparum blood samples in 2015-2019 were included and 7.3% (31/425) carried Pfk13 mutations. Out of the isolates that carried Pfk13 mutations, 54.8% (17/31) were nonsynonymous polymorphisms. The mutant alleles A578S, Q613H, C469C, and S549S in Pfk13 were the more frequently detected allele, the mutation rate was the same as 9.7% (3/31). Another allele Pfk13 C580Y, closely associated with artemisinin (ART) resistance, was found as 3.2% (2/31), which was found in Cambodia. A total of 14 mutant isolates were identified in Western Africa countries (45.2%, 14/31). For the Pfcrt gene, the mutation rate was 18.1% (77/425). T₇₆T₃₅₆ and T₇₆ were more frequent in all 13 different haplotypes with 26.0% (20/77) and 23.4% (18/77). The CVIET and CVIKT mutant at loci 72-76 have exhibited a prevalence of 19.5% (15/77) and 3.9% (3/77), respectively. The CVIET was mainly observed in samples from Congo (26.7%, 4/15) and Mozambique (26.7%, 4/15). No mutations were found at loci 97, 101 and 145. For polymorphisms at locus 356, a total of 24 isolates were identified and mainly from Congo (29.2%, 7/24).

CONCLUSION

These findings indicate a low prevalence of Pfk13 in the African isolates. However, the emergence and increase in the new alleles Pfcrt I356T, reveals a potential risk of drug pressure in PPQ among migrant workers returned from Africa. Therefore, continuous molecular surveillance of Pfcrt mutations and in vitro susceptibility tests related to PPQ are necessary.

Multidisciplinary Investigations of Sustained Malaria Transmission in the Greater Mekong Subregion

In the course of malaria elimination in the Greater Mekong Subregion (GMS), malaria epidemiology has experienced drastic spatiotemporal changes with residual transmission concentrated along international borders and the rising predominance of Plasmodium vivax. The emergence of Plasmodium falciparum parasites resistant to artemisinin and partner drugs renders artemisinin-based combination therapies less effective while the potential spread of multidrug-resistant parasites elicits concern. Vector behavioral changes and insecticide resistance have reduced the effectiveness of core vector control measures. In recognition of these problems, the Southeast Asian International Center of Excellence for Malaria Research (ICEMR) has been conducting multidisciplinary research to determine how human migration, antimalarial drug resistance, vector behavior, and insecticide resistance sustain malaria transmission at international borders. These efforts allow us to comprehensively understand the ecology of border malaria transmission and develop population genomics tools to identify and track parasite introduction. In addition to employing in vivo, in vitro, and molecular approaches to monitor the emergence and spread of drug-resistant parasites, we also use genomic and genetic methods to reveal novel mechanisms of antimalarial drug resistance of parasites. We also use omics and population genetics approaches to study insecticide resistance in malaria vectors and identify changes in mosquito community structure, vectorial potential, and seasonal dynamics. Collectively, the scientific findings from the ICEMR research activities offer a systematic view of the factors sustaining residual malaria transmission and identify potential solutions to these problems to accelerate malaria elimination in the GMS.

The primate malaria parasites Plasmodium malariae, Plasmodium brasilianum and Plasmodium ovale spp.: genomic insights into distribution, dispersal and host transitions

During the twentieth century, there was an explosion in understanding of the malaria parasites infecting humans and wild primates. This was built on three main data sources: from detailed descriptive morphology, from observational histories of induced infections in captive primates, syphilis patients, prison inmates and volunteers, and from clinical and epidemiological studies in the field. All three were wholly dependent on parasitological information from blood-film microscopy, and The Primate Malarias” by Coatney and colleagues (1971) provides an overview of this knowledge available at that time. Here, 50 years on, a perspective from the third decade of the twenty-first century is presented on two pairs of primate malaria parasite species. Included is a near-exhaustive summary of the recent and current geographical distribution for each of these four species, and of the underlying molecular and genomic evidence for each. The important role of host transitions in the radiation of Plasmodium spp. is discussed, as are any implications for the desired elimination of all malaria species in human populations. Two important questions are posed, requiring further work on these often ignored taxa. Is Plasmodium brasilianum, circulating among wild simian hosts in the Americas, a distinct species from Plasmodium malariae? Can new insights into the genomic differences between Plasmodium ovale curtisi and Plasmodium ovale wallikeri be linked to any important differences in parasite morphology, cell biology or clinical and epidemiological features?

Variation in chemical composition and antimalarial activities of two samples of Terminalia albida collected from separate sites in Guinea

BACKGROUND

The disparity of harvesting locations can influence the chemical composition of a plant species, which could affect its quality and bioactivity. Terminalia albida is widely used in traditional Guinean medicine whose activity against malaria has been validated in vitro and in murine models. The present work investigated the antimalarial properties and chemical composition of two samples of T. albida collected from different locations in Guinea.

METHOD

T. albida samples were collected in different locations in Guinea, in Dubréka prefecture (West maritime Guinea) and in Kankan prefecture (eastern Guinea). The identity of the samples was confirmed by molecular analysis. In vitro antiplasmodial activity of the two extracts was determined against the chloroquine resistant strain PfK1. In vivo, extracts (100 mg/kg) were tested in two experimental murine models, respectively infected with P. chabaudi chabaudi and P. berghei ANKA. The chemical composition of the two samples was assessed by ultra-high-performance liquid chromatography coupled to high resolution mass spectrometry.

RESULTS

In vitro, the Dubréka sample (TaD) was more active with an IC50 of 1.5 μg/mL versus 8.5 μg/mL for the extract from Kankan (TaK). In vivo, the antiparasitic effect of TaD was substantial with 56% of parasite inhibition at Day 10 post-infection in P. chabaudi infection and 61% at Day 8 in P. berghei model, compared to 14 and 19% inhibition respectively for the treatment with TaK. In addition, treatment with TaD further improved the survival of P. berghei infected-mice by 50% at Day 20, while the mortality rate of mice treated with Tak was similar to the untreated group. The LC/MS analysis of the two extracts identified 38 compounds, 15 of which were common to both samples while 9 and 14 other compounds were unique to TaD and TaK respectively.

CONCLUSION

This study highlights the variability in the chemical composition of the species T. albida when collected in different geographical locations. These chemical disparities were associated with variable antimalarial effects. From a public health perspective, these results underline the importance of defining chemical fingerprints related to botanical species identification and to biological activity, for the plants most commonly used in traditional medicine.

New insights into malaria vector bionomics in Lao PDR: a nationwide entomology survey

BACKGROUND

In Laos, the malaria burden remains high despite a significant reduction of cases during the last decade. In the context of the disease elimination by 2030, a nationwide entomological survey was conducted to better understand the distribution, abundance and behaviour of major malaria vectors (Anopheles spp.) in the country.

METHODS

Mosquito collections were implemented in ten villages from ten provinces during the rainy and dry seasons of 2014 and 2015 by using human landing catch (HLC) and cow bait collection (CBC) methods. After morphological identification in the field, molecular identification of the sibling species of Anopheles mosquitoes from the Funestus, Leucosphyrus, and Maculatus groups were determined using PCR specific alleles. A screening of Plasmodium falciparum and Plasmodium vivax infections in the vectors was carried out by quantitative PCR assays.

RESULTS

A total of 14,146 adult mosquitoes representing 25 different Anopheles species were collected and morphologically identified. Molecular identification revealed the presence of 12 sibling species within the main primary vector groups, including Anopheles maculatus, Anopheles rampae, Anopheles sawadwongporni, Anopheles pseudowillmori, Anopheles dravidicus, Anopheles minimus, Anopheles aconitus, Anopheles pampanai, Anopheles harrisoni, Anopheles dirus, Anopheles baimaii, Anopheles nemophilous. Anopheles maculatus and An. minimus were predominant during both the dry and rainy seasons, but showed highly zoophilic preferences (Zoophilic index of 98% and 95%, respectively). Overall, 22% of the total malaria vectors were collected between 10:00 PM and 5:00 AM indoors when people are sleeping. Twenty-seven percent of primary and secondary vectors were collected outdoors before 10:00 PM or after 5:00 AM, times when people are usually awake and outdoors. Only two specimens were positive for P. falciparum, one An. aconitus from Phongsaly and one An. minimus from Vientiane Province CONCLUSIONS: The results indicate that people living in rural areas in Laos are constantly exposed to malaria vectors throughout the year and specifically outdoors. The use of LLINs/IRS remains important but innovative tools and new strategies are needed to address locally, the early and outdoor malaria transmission. Lack of expertise in general entomological methods may further exacerbate the situation.

Triple Artemisinin-Based Combination Therapies for Malaria - A New Paradigm?

Recent gains in the fight against malaria are threatened by the emergence and spread of artemisinin and partner drug resistance in Plasmodium falciparum in the Greater Mekong Subregion (GMS). When artemisinins are combined with a single partner drug, all recommended artemisinin-based combination therapies have shown reduced efficacy in some countries in the GMS at some point. Novel drugs are not available for the near future. Triple artemisinin-based combination therapies, combining artemisinins with two currently available partner drugs, will provide one of the last remaining safe and effective treatments for falciparum malaria that can be deployed rapidly in the GMS, whereas their deployment beyond the GMS could delay or prevent the global emergence and spread of resistance to currently available drugs.

Origin and Spread of Evolving Artemisinin-Resistant Plasmodium falciparum Malarial Parasites in Southeast Asia

In this review, we provide an epidemiological history of the emergence and ongoing spread of evolving Plasmodium falciparum artemisinin resistance (ARTR). Southeast Asia has been the focal point for emergence and spread of multiple antimalarial drug resistance phenomena, and is once again for evolving ARTR, also known as the "delayed clearance phenotype" (DCP). The five countries most impacted, Cambodia, Thailand, Myanmar, Laos, and Vietnam, each have complex histories of antimalarial drug use over many decades, which have in part molded the use of various artemisinin combination therapies (ACTs) within each country. We catalog the use of ACTs, evolving loss of ACT efficacy, and the frequency of pfk13 mutations (mutations associated with ARTR) in the Greater Mekong Subregion and map the historical spread of ARTR/DCP parasites. These data should assist improved surveillance and deployment of next-generation ACTs.