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The absence of the Duffy protein at the surface of erythrocytes was considered for decades to confer full protection against Plasmodium vivax as this blood group is the receptor for the key parasite ligand P. vivax Duffy binding protein (PvDBP). However, it is now clear that the parasite is able to break through this protection and induce clinical malaria in Duffy-negative people, although the underlying mechanisms are still not understood. Here, we briefly review the evidence of Duffy-negative infections by P. vivax and summarize the current hypothesis at the basis of this invasion process. We discuss those in the perspective of malaria-elimination challenges, notably in African countries.

Studies of Plasmodium vivax gene expression are complicated by the lack of in vitro culture system and the difficulties associated with studying clinical infections that often contain multiple clones and a mixture of parasite stages. Here, we characterize the transcriptomes of P. vivax parasites from 26 malaria patients. We show that most parasite mRNAs derive from trophozoites and that the asynchronicity of P. vivax infections is therefore unlikely to confound gene expression studies. Analyses of gametocyte genes reveal two distinct clusters of co-regulated genes, suggesting that male and female gametocytes are independently regulated. Finally, we analyze gene expression changes induced by chloroquine and show that this antimalarial drug efficiently eliminates most P. vivax parasite stages but, in contrast to P. falciparum , does not affect trophozoites. Plasmodium vivax biology is not well understood, due to a lack of in vitro culture systems and difficulties associated with studying clinical blood samples. Here, Kim et al. use gene expression profiles from P. vivax infected patient blood and show stage-specific chloroquine response and differential regulation of male and female gametocytes.

Dengue is one of the most widespread mosquito-borne diseases in the world. The causative agent, dengue virus (DENV), is primarily transmitted by the mosquito Aedes aegypti, a species that has proved difficult to control using conventional methods. The discovery that A. aegypti transinfected with the wMel strain of Wolbachia showed limited DENV replication led to trial field releases of these mosquitoes in Cairns, Australia as a biocontrol strategy for the virus. Field collected wMel mosquitoes that were challenged with three DENV serotypes displayed limited rates of body infection, viral replication and dissemination to the head compared to uninfected controls. Rates of dengue infection, replication and dissemination in field wMel mosquitoes were similar to those observed in the original transinfected wMel line that had been maintained in the laboratory. We found that wMel was distributed in similar body tissues in field mosquitoes as in laboratory ones, but, at seven days following blood-feeding, wMel densities increased to a greater extent in field mosquitoes. Our results indicate that virus-blocking is likely to persist in Wolbachia-infected mosquitoes after their release and establishment in wild populations, suggesting that Wolbachia biocontrol may be a successful strategy for reducing dengue transmission in the field.

Antigenic variation, the capacity to produce a range of variable antigens, is a well-described strategy of Plasmodium and other parasites to evade host immunity. Here, we show that gene amplification is an additional evasion mechanism used by Plasmodium vivax to escape humoral immunity targeting PvDBP, the key ligand involved in reticulocyte invasion. PvDBP gene amplification leads to increased mRNA levels and protects P. vivax in vitro against invasion inhibitory human monoclonal antibodies targeting a conserved binding domain of DBP. Patient samples suggest that parasites with increased pvdbp copy number are able to infect individuals with naturally acquired antibodies highly blocking the binding of PvDBP to the Duffy receptor. These results show that gene copy number variation affect the parasite’s ability to evade anti-PvDBP humoral immunity. Duffy binding protein (DBP) of Plasmodium vivax is important for invasion and is a potential vaccine candidate. Here, the authors show that PvDBP gene amplification protects P vivax in vitro against invasion inhibitory human monoclonal antibodies and is associated to infection of patients with PvDBP binding inhibitory antibodies.

Triple artemisinin-based combination therapies (TACTs) have been proposed to delay the emergence of multidrug-resistant Plasmodium falciparum by combining two partner drugs with an artemisinin derivative. Among these, mefloquine–piperaquine (MQ–PPQ) is a leading candidate, based on the assumption that simultaneous resistance to both partner drugs would be difficult to develop. Here, we assess the efficacy and resistance potential of MQ–PPQ using Cambodian clinical isolates with distinct resistance profiles. We find that MQ resistance confers significant cross-tolerance to the MQ–PPQ combination, whereas PPQ-resistant and -sensitive strains remain susceptible. Under repeated MQ–PPQ pressure for four months, parasites rapidly acquire MQ–PPQ tolerance, driven by pfmdr1 amplification. Mechanistic investigations reveal that MQ inhibits PPQ accumulation in a dose-dependent manner, providing a functional explanation for the compromised efficacy of the combination. These findings demonstrate that MQ resistance alone can undermine MQ–PPQ TACT efficacy, calling into question the strategic rationale of this combination and underscoring the need for alternative regimens with a lower risk of resistance selection. Triple artemisinin-based combination therapies, including mefloquine–piperaquine (MQ–PPQ), may delay emergence of multidrug-resistant strains. Here the authors show that resistance to mefloquine alone reduces the efficacy of the MQ-PPQ combination therapy, and that the interaction between the two drugs further inhibits piperaquine’s activity.

The documentation of Plasmodium vivax malaria across Africa especially in regions where Duffy negatives are dominant suggests possibly alternative erythrocyte invasion mechanisms. While the transcriptomes of the Southeast Asian and South American P . vivax are well documented, the gene expression profile of P . vivax in Africa is unclear. In this study, we examined the expression of 4,404 gene transcripts belong to 12 functional groups and 43 erythrocyte binding gene candidates in Ethiopian isolates and compared them with the Cambodian and Brazilian P . vivax transcriptomes. Overall, there were 10–26% differences in the gene expression profile amongst geographical isolates, with the Ethiopian and Cambodian P . vivax being most similar. Majority of the gene transcripts involved in protein transportation, housekeeping, and host interaction were highly transcribed in the Ethiopian isolates. Members of the reticulocyte binding protein PvRBP 2a and PvRBP 3 expressed six-fold higher than Duffy binding protein PvDBP 1 and 60-fold higher than PvEB P/ DBP 2 in the Ethiopian isolates. Other genes including PvMSP3 . 8 , PvMSP3 . 9 , PvTRAG2 , PvTRAG14 , and PvTRAG22 also showed relatively high expression. Differential expression patterns were observed among geographical isolates, e.g., PvDBP 1 and PvEB P/ DBP 2 were highly expressed in the Cambodian but not the Brazilian and Ethiopian isolates, whereas PvRBP 2a and PvRBP 2b showed higher expression in the Ethiopian and Cambodian than the Brazilian isolates. Compared to Pvs 25, gametocyte genes including PvAP2-G , PvGAP (female gametocytes), and Pvs 47 (male gametocytes) were highly expressed across geographical samples.

Plasmodium vivax malaria remains a significant global health challenge, complicated by the parasite’s ability to form dormant liver stages (hypnozoites) that cause relapses. Radical cure of P. vivax malaria requires administration of a hypnozoitocidal drug, such as primaquine or tafenoquine. However, these drugs can cause severe haemolysis in individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency. G6PD deficiency is caused by more than 230 different variants at the gene level that confer different degrees of deficiency phenotypically. Understanding the distribution of different G6PD variants in affected populations is essential to inform safer antimalarial treatment strategies. This study aimed to develop a cost-effective sequencing assay targeting key regions of the G6PD gene, suitable for field deployment. A novel assay based on Nanopore technology was designed to amplify two amplicons covering exon 3 to exon 13, focusing on known variants associated with enzyme deficiency. A total of 79 samples from individuals in Cambodia, Vietnam, Afghanistan, and China were sequenced, and a bioinformatics pipeline was created for the targeted variant calling of 192 G6PD SNP mutations. The assay demonstrated reliable detection of known variants, with high concordance between runs, within runs, and with Sanger sequencing. The Nanopore MinION long-amplicon sequencing assay offers a robust and portable solution for large-scale G6PD genotyping in low-resource settings, that will improve malaria control and elimination strategies by enabling safer antimalarial treatment.

Background Rapid elimination of Plasmodium falciparum malaria in Cambodia is a goal with both national and international significance. Transmission of malaria in Cambodia is limited to forest environments, and the main population at risk consists of forest-goers who rely on forest products for income or sustenance. The ideal interventions to eliminate malaria from this population are unknown. Methods In two forested regions of Cambodia, forest-goers were trained to become forest malaria workers (FMWs). In one region, FMWs performed mass screening and treatment, focal screening and treatment, and passive case detection inside the forest. In the other region, FMWs played an observational role for the first year, to inform the choice of intervention for the second year. In both forests, FMWs collected blood samples and questionnaire data from all forest-goers they encountered. Mosquito collections were performed in each forest. Results Malaria prevalence by PCR was high in the forest, with 2.3–5.0% positive for P. falciparum and 14.6–25.0% positive for Plasmodium vivax among forest-goers in each study site. In vectors, malaria prevalence ranged from 2.1% to 9.6%, but no P. falciparum was observed. Results showed poor performance of mass screening and treatment, with sensitivity of rapid diagnostic tests equal to 9.1% (95% CI 1.1%, 29.2%) for P. falciparum and 4.4% (95% CI 1.6%, 9.2%) for P. vivax . Malaria infections were observed in all demographics and throughout the studied forests, with no clear risk factors emerging. Conclusions Malaria prevalence remains high among Cambodian forest-goers, but performance of rapid diagnostic tests is poor. More adapted strategies to this population, such as intermittent preventive treatment of forest goers, should be considered.

Background Introduced Wolbachia bacteria can influence the susceptibility of Aedes aegypti mosquitoes to arboviral infections as well as having detrimental effects on host fitness. Previous field trials demonstrated that the w Mel strain of Wolbachia effectively and durably invades Ae. aegypti populations. Here we report on trials of a second strain, w MelPop-PGYP Wolbachia, in field sites in northern Australia (Machans Beach and Babinda) and central Vietnam (Tri Nguyen, Hon Mieu Island), each with contrasting natural Ae. aegypti densities. Methods Mosquitoes were released at the adult or pupal stages for different lengths of time at the sites depending on changes in Wolbachia frequency as assessed through PCR assays of material collected through Biogents-Sentinel (BG-S) traps and ovitraps. Adult numbers were also monitored through BG-S traps. Changes in Wolbachia frequency were compared across hamlets or house blocks. Results Releases of adult w MelPop -Ae. aegypti resulted in the transient invasion of w MelPop in all three field sites. Invasion at the Australian sites was heterogeneous, reflecting a slower rate of invasion in locations where background mosquito numbers were high. In contrast, invasion across Tri Nguyen was relatively uniform. After cessation of releases, the frequency of w MelPop declined in all sites, most rapidly in Babinda and Tri Nguyen. Within Machans Beach the rate of decrease varied among areas, and w MelPop was detected for several months in an area with a relatively low mosquito density. Conclusions These findings highlight challenges associated with releasing Wolbachia - Ae. aegypti combinations with low fitness, albeit strong virus interference properties, as a means of sustainable control of dengue virus transmission.

New therapeutics are necessary for preventing Plasmodium vivax malaria due to easy transmissibility and dormancy in the liver that increases the clinical burden due to recurrent relapse. In this manuscript we characterize 12 Pv Apical Membrane Antigen 1 (PvAMA1) specific human monoclonal antibodies from Peripheral Blood Mononuclear Cells of a Pv-exposed individual. PvAMA1 is essential for sporozoite and merozoite invasion, making it a unique therapeutic target. We show that humAb 826827 blocks the invasion of human reticulocytes using Pv clinical isolates and inhibits sporozoite invasion of human hepatocytes in vitro (IC 50 of 0.3 – 3.7 µg/mL). Inoculation of human liver transgenic (FRG-humHep) female mice with humAb 826827 significantly reduces liver infection in vivo. The crystal structure of rPvAMA1 bound to 826827 shows that 826827 partially occupies the highly conserved hydrophobic groove in PvAMA1 that binds its known receptor, RON2. We have isolated a potent humAb that is isolate-transcendent, blocks both pre-erythrocytic and blood stage infection, and could be a potential therapy for Pv. Here the authors isolate monoclonal antibodies specific for Plasmodium vivax apical membrane antigen 1, and characterize the epitope of one antibody that inhibits invasion of reticulocytes and hepatocytes, and reduces liver infection in a mouse model.