Evidence and implications of mortality associated with acute Plasmodium vivax malaria

Thrombocytopenia and Epistaxis Complicating Plasmodium falciparum Malaria: Case Report Study

Malaria is one of the vector-borne diseases with major public health problems to date, especially in endemic areas. Malaria is usually associated with various degrees of reduced red blood counts, and thrombocytopenia is a common association of malaria, but it is rarely associated with hemorrhagic manifestations. This case report presents two Sudanese patients, who presented to a private clinic in North Bahri. The patients were infected with Plasmodium falciparum; they developed thrombocytopenia and were presented clinically with epistaxis. A 36-year-old male and a 41-year-old male presented with the clinical features of malaria and epistaxis and were diagnosed with P. falciparum malaria. Both patients had significant thrombocytopenia in complete blood count (CBC). They showed clinical and laboratory improvement of thrombocytopenia after successful treatment of malaria. Although bleeding is a rare complication of malaria associated with thrombocytopenia, it should be considered even if it presents as a minor bleeding such as epistaxis or bleeding from gum.

Serology reveals comparable patterns in the transmission intensities of Plasmodium falciparum and Plasmodium vivax in Langkat district, North Sumatera Province, Indonesia

Introduction

The incidence of malaria in Indonesia has declined significantly over the last few decades. Thus, a demand for more sensitive techniques to describe low levels of transmission in the country is important. This study was conducted to evaluate antibody response to Plasmodium falciparum and Plasmodium vivax in an area nearing elimination in North Sumatera Province, Indonesia.

Methods

A cross-sectional survey was conducted in Langkat district, North Sumatera Province, in June 2019. Basic demographic data and filter paper blood spots were collected from 339 participants. Antibody responses to two P. falciparum (PfAMA-1 and PfMSP-119) and two P. vivax (PvAMA-1 and PvMSP-119) antigens were measured using indirect enzyme-linked immunosorbent assay (ELISA). Seroconversion rates (SCR) were estimated by fitting a simple reversible catalytic model to seroprevalence data for each antibody. Multiple logistic regression was used to investigate factors associated with exposure.

Results

The overall malaria seroprevalence was 10.6% for PfAMA-1, 13% for PfMSP-119, 18.6% for PvAMA-1, and 7.4% for PvMSP-119. Seropositive individuals for P. falciparum (PfAMA-1/PfMSP-119) and P. vivax (PvAMA-1/PvMSP-119) were similar at 20.7%, with no significant differences observed between age groups (p > 0.05). Based on the reversible catalytic model, the calculated SCRs indicated a higher level of P. falciparum transmission than P. vivax using all tested antigens. In the adjusted model, only spending nights in the forest was associated with P. vivax seropositivity (odd ratio: 3.93, p < 0.001).

Conclusion

The analysis of community-based serological data helps describe the similar levels of P. falciparum and P. vivax transmission in the Langkat district. The use of a serological approach enhances the detection of past exposure, aiding in the identification of epidemiological risk factors and malaria surveillance in low transmission settings in Indonesia.

Experiences, perceptions and ethical considerations of the malaria infection study in Thailand

BACKGROUND

Thailand has made significant progress in malaria control efforts in the past decade, with a decline in the number of reported cases. However, due to cross-border movements over the past 5 years, reported malaria cases in Thailand have risen. The Malaria Infection Study in Thailand (MIST) involves deliberate infection of healthy volunteers with Plasmodium vivax malaria parasites, and the assessment of the efficacy of potential vaccine and drug candidates in order to understand acquired protection against malaria parasites.

METHODS

This paper drew from ethics and social science qualitative study called MIST-ETHICS embedded within the MIST studies. MIST-ETHICS aimed to describe and understand the experiences, perceptions and ethical considerations of the MIST studies. Data were obtained from semi-structured interviews and a focus group discussion. A total of 46 participants participated in MIST-ETHICS .

RESULTS

Three major themes emerged: experiences and perceptions of MIST, reasons for joining MIST, and ethical considerations. We found that although compensation was a motivation for participation, this was secondary to it being beneficial to self (health checks; link to health networks; building merit) and others (medical research contribution; altruism). Participants expressed varied opinions regarding the requirement of a university degree as one of the inclusion criteria for MIST.

CONCLUSIONS

Our study revealed widespread concerns about long-term health effects and safety. Ethical considerations, including obtaining valid informed consent and ensuring participant inclusivitiy, were deem essential. Despite some debate regarding eligibility criteria, most participants agreed that the informed consent process was robust, accompanied by a strong sense of responsibility to contribute to the greater good. We emphasize the importance of continuously gathering participants' feedback for quality control, such as improving information materials to clarify the purpose of initial phases, their contributing to later phases, and the rationale behind each selection criterion.

TRIAL REGISTRATION

This manuscript is part of the clinical trials registered under ClinicalTrials.gov IDs NCT04083508 (MIST1) registered on 5 Sep 2019 and NCT05071079 (MIST2) registered on 28 July 2021. However, the manuscript pertains to a qualitative study that does not require trial registration.

Probing the Clinical, Laboratory, and Sociodemographic Factors Associated with Malaria: A Case-Control Study

Background

The National Malaria Elimination Program (NMEP) has helped reduce the mortality from malaria in India, and there are alarmingly high mortality rates from anemia in certain geographical regions.

Aim

To assess the clinical, laboratory, and sociodemographic factors associated with malaria from P. falciparum and P. vivax.

Methods

This retrospective record-based clinical study subjects with malaria were further divided into P. vivax and P. falciparum cases. In all the cases, the clinical, laboratory, and sociodemographic factors were assessed. Data gathered were analyzed statistically.

Results

During the study period, 222 cases of malaria were assessed where 22.52% (n = 50) and 74.48% (n = 172) cases were due to P. falciparum and P. vivax, respectively. Hepatomegaly was common in P. falciparum cases and splenomegaly in P. vivax cases. Thrombocytopenia was seen in 58.1% (n = 100) and 72% (n = 36) subjects with P. vivax and P. falciparum cases. No significant difference was seen in other laboratory parameters.

Conclusions

Clinical, laboratory, and sociodemographic factors associated with malaria from P. falciparum and P. vivax have no statistically significant difference.

The PvRBP2b-TfR1 interaction is not essential for reticulocytes invasion by Plasmodium vivax isolates from Cambodia

Plasmodium vivax is the most widespread of the different Plasmodium species able to infect humans and is responsible for most malaria cases outside Africa. An effective, strain-transcending vaccine that alleviates or suppresses erythrocyte invasion would be a game-changer in eliminating vivax malaria. Recently, the binding of P. vivax Reticulocyte Binding Protein 2b (PvRBP2b) to human Transferrin receptor (TfR1) has been described as essential for reticulocyte invasion, making this parasite protein an appealing vaccine candidate. Here, using P. vivax Cambodian clinical isolates in robust ex vivo invasion assays, we show that anti-PvRBP2b polyclonal and monoclonal antibodies that inhibit binding of PvRBP2b to TfR1 do not block P. vivax invasion into reticulocytes even at high concentrations. Anti-TfR1 antibodies do not inhibit P. vivax invasion either. Combinations at high concentrations of human monoclonal antibodies targeting different PvRBP2b epitopes do not inhibit invasion. Combinations of anti-PvRBP2b with anti-PvDBP do not enhance invasion inhibition caused by anti-PvDBP alone. We also show that the invasion of Cambodian P. vivax is trypsin-resistant while TfR1 is trypsin-sensitive, and we demonstrate that TfR1 is not recycled following trypsin treatment. We determined the PvRBP2b sequence of all isolates used in the invasion assays and analyzed polymorphism within epitopes recognized by anti-PvRBP2b antibodies. We show that polymorphism does not explain the absence of neutralization. Anti-PvRBP2b polyclonal antibodies recognized all four isolates tested in immunofluorescence assays while not inhibiting P. vivax invasion. Overall, our results demonstrate that PvRBP2b binding to TfR1 is not essential for invasion into reticulocytes of P. vivax Cambodian strains questioning the relevance of PvRBP2b as vaccine candidate.

An Uncommon Case of Plasmodium vivax Malaria with Disseminated Intravascular Coagulation: Rare Case Report with Review of Literature

ABSTRACT

Malaria is a severe health issue in India despite government efforts. Malaria has many complications, some of which can be life-threatening. Disseminated intravascular coagulation (DIC) is a prominent malaria complication, besides renal failure, cerebral malaria, pulmonary edema, and anemia. We report a young man with Plasmodium vivax malaria who developed septic shock due to DIC. A 25-year-old male had a fever, abdominal pain, vomiting, and nausea for 5 days. On clinical examination, the patient was in distress and had a fever of 102.6°F with a blood pressure of 86/46 mmHg. A complete blood count revealed anemia, leukocytopenia, and severe thrombocytopenia. Peripheral blood smear findings showed a P. vivax parasite in red blood cells with the presence of a few schistocytes. Further coagulation tests showed raised prothrombin, partial thromboplastin time, and d-dimer. DIC and septic shock required critical care unit admission. Conservative treatment with artesunate and lumefantrine completely cured him. This unusual case shows that P. vivax causes severe malaria and its morbid consequences. It stresses early diagnosis and treatment to prevent mortality and morbidity.

Transmission-blocking activities of artesunate, chloroquine, and methylene blue on Plasmodium vivax gametocytes

Plasmodium vivax is now the main cause of malaria outside Africa. The gametocytocidal effects of antimalarial drugs are important to reduce malaria transmissibility, particularly in low-transmission settings, but they are not well characterized for P. vivax. The transmission-blocking effects of chloroquine, artesunate, and methylene blue on P. vivax gametocytes were assessed. Blood specimens were collected from patients presenting with vivax malaria, incubated with or without the tested drugs, and then fed to mosquitos from a laboratory-adapted colony of Anopheles dirus (a major malaria vector in Southeast Asia). The effects on oocyst and sporozoite development were analyzed under a multi-level Bayesian model accounting for assay variability and the heterogeneity of mosquito Plasmodium infection. Artesunate and methylene blue, but not chloroquine, exhibited potent transmission-blocking effects. Gametocyte exposures to artesunate and methylene blue reduced the mean oocyst count 469-fold (95% CI: 345 to 650) and 1,438-fold (95% CI: 970 to 2,064), respectively. The corresponding estimates for the sporozoite stage were a 148-fold reduction (95% CI: 61 to 470) and a 536-fold reduction (95% CI: 246 to 1,311) in the mean counts, respectively. In contrast, high chloroquine exposures reduced the mean oocyst count only 1.40-fold (95% CI: 1.20 to 1.64) and the mean sporozoite count 1.34-fold (95% CI: 1.12 to 1.66). This suggests that patients with vivax malaria often remain infectious to anopheline mosquitos after treatment with chloroquine. Use of artemisinin combination therapies or immediate initiation of primaquine radical cure should reduce the transmissibility of P. vivax infections.

Evaluation of combination vaccines targeting transmission of Plasmodium falciparum and P. vivax

Transmission-blocking vaccines interrupting malaria transmission within mosquitoes represent an ideal public health tool to eliminate malaria at the population level. Plasmodium falciparum and P. vivax account for more than 90% of the global malaria burden, co-endemic in many regions of the world. P25 and P48/45 are two leading candidates for both species and have shown promising transmission-blocking activity in preclinical and clinical studies. However, neither of these target antigens as individual vaccines has induced complete transmission inhibition in mosquitoes. In this study, we assessed immunogenicity of combination vaccines based on P25 and P48/45 using a DNA vaccine platform to broaden vaccine specificity against P. falciparum and P. vivax. Individual DNA vaccines encoding Pvs25, Pfs25, Pvs48/45 and Pfs48/45, as well as various combinations including (Pvs25 + Pvs48/45), (Pfs25 + Pfs48/45), (Pvs25 + Pfs25), and (Pvs48/45 + Pfs48/45), were evaluated in mice using in vivo electroporation. Potent antibody responses were induced in mice immunized with individual and combination DNA vaccines, and specific antibody responses were not compromised when combinations of DNA vaccines were evaluated against individual DNA vaccines. The anti-Pvs25 IgG from individual and combination groups revealed concentration-dependent transmission-reducing activity (TRA) in direct membrane feeding assays (DMFA) using blood from P. vivax-infected donors in Brazil and independently in ex vivo MFA using Pvs25-transgenic P. berghei. Similarly, anti-Pfs25 and anti-Pfs48/45 IgGs from mice immunized with Pfs25 and Pfs48/45 DNA vaccines individually and in various combinations revealed antibody dose-dependent TRA in standard membrane feeding assays (SMFA) using culture-derived P. falciparum gametocytes. However, antibodies induced by immunization with Pvs48/45 DNA vaccines were ineffective in DMFA and require further vaccine construct optimization, considering the possibility of induction of both transmission-blocking and transmission-enhancing antibodies revealed by competition ELISA. These studies provide a rationale for combining multiple antigens to simultaneously target transmission of malaria caused by P. falciparum and P. vivax.

Immunogenicity and transmission-blocking potential of quiescin sulfhydryl oxidase in Plasmodium vivax

Background

Transmission-blocking vaccines (TBVs) can effectively prevent the community's spread of malaria by targeting the antigens of mosquito sexual stage parasites. At present, only a few candidate antigens have demonstrated transmission-blocking activity (TBA) potential in P. vivax. Quiescin-sulfhydryl oxidase (QSOX) is a sexual stage protein in the rodent malaria parasite Plasmodium berghei and is associated with a critical role in protein folding by introducing disulfides into unfolded reduced proteins. Here, we reported the immunogenicity and transmission-blocking potency of the PvQSOX in P. vivax.

Methods and findings

The full-length recombinant PvQSOX protein (rPvQSOX) was expressed in the Escherichia coli expression system. The anti-rPvQSOX antibodies were generated following immunization with the rPvQSOX in rabbits. A parasite integration of the pvqsox gene into the P. berghei pbqsox gene knockout genome was developed to express full-length PvQSOX protein in P. berghei (Pv-Tr-PbQSOX). In western blot, the anti-rPvQSOX antibodies recognized the native PvQSOX protein expressed in transgenic P. berghei gametocyte and ookinete. In indirect immunofluorescence assays, the fluorescence signal was detected in the sexual stages, including gametocyte, gamete, zygote, and ookinete. Anti-rPvQSOX IgGs obviously inhibited the ookinetes and oocysts development both in vivo and in vitro using transgenic parasites. Direct membrane feeding assays of anti-rPvQSOX antibodies were conducted using four field P. vivax isolates (named isolates #1-4) in Thailand. Oocyst density in mosquitoes was significantly reduced by 32.00, 85.96, 43.52, and 66.03% with rabbit anti-rPvQSOX antibodies, respectively. The anti-rPvQSOX antibodies also showed a modest reduction of infection prevalence by 15, 15, 20, and 22.22%, respectively, as compared to the control, while the effect was insignificant. The variation in the DMFA results may be unrelated to the genetic polymorphisms. Compared to the P.vivax Salvador (Sal) I strain sequences, the pvqsox in isolate #1 showed no amino acid substitution, whereas isolates #2, #3, and #4 all had the M361I substitution.

Conclusions

Our results suggest that PvQSOX could serve as a potential P. vivax TBVs candidate, which warrants further evaluation and optimization.

Extracellular vesicles as biomarkers in parasitic disease diagnosis

Parasitic diseases constitute a major global health problem, affecting millions of people worldwide. Recent advances in the study of extracellular vesicles (EVs) have opened up new strategies for biomarker discovery in protozoan and helminth infections. Analyses of EVs in cultures and biological fluids have identified numerous potential biomarkers that could be useful for early and differential diagnosis, monitoring therapeutic responses, and the overall management and control of these diseases. Despite the potential of these biomarkers, several challenges must be addressed, including limited research, the need for standardized protocols, and the reproducibility of results across studies. In many parasitic infections, EVs have been obtained from various sample types, including plasma from human patients and mouse models, as well as cultures of the parasites at different stages. EVs were isolated by various methods and predominantly characterized through proteomic analysis or RNA sequencing to assess their cargo and identify potential biomarkers. These biomarker candidates were investigated and validated using different assays such as ELISA, Western Blot, and ROC curves. Overall, the use of EVs is considered a promising new diagnostic strategy for parasite infections, but further research with larger cohorts, standardized methods, and additional validation tests are essential for effective diagnosis and management of these diseases.

Structure-based design of a Plasmodium vivax Duffy-binding protein immunogen focuses the antibody response to functional epitopes

The Duffy-binding protein (DBP) is a promising antigen for a malaria vaccine that would protect against clinical symptoms caused by Plasmodium vivax infection. Region II of DBP (DBP-II) contains the receptor-binding domain that engages host red blood cells, but DBP-II vaccines elicit many non-neutralizing antibodies that bind distal to the receptor-binding surface. Here, we engineered a truncated DBP-II immunogen that focuses the immune response to the receptor-binding surface. This immunogen contains the receptor-binding subdomain S1S2 and lacks the immunodominant subdomain S3. Structure-based computational design of S1S2 identified combinatorial amino acid changes that stabilized the isolated S1S2 without perturbing neutralizing epitopes. This immunogen elicited DBP-II-specific antibodies in immunized mice that were significantly enriched for blocking activity compared to the native DBP-II antigen. This generalizable design process successfully stabilized an integral core fragment of a protein and focused the immune response to desired epitopes to create a promising new antigen for malaria vaccine development.

Race, immunity, and lifespan: Unraveling the effect of early-life exposure to malaria risk on lifespan

We investigate a historical experience to measure the long-term effect of malaria on lifespan among infected survivors and identify a factor that mitigates malaria's effect. Using a sample of Union Army veterans born during the mid-19th century and their lifetime records, we show that exposure to high risk of malaria at birth or in early life substantially shortened their lifespan. The legacy of exposure to malaria is robust while controlling for lifetime socioeconomic and health conditions, fixed effects, and considering selection bias. Additionally, we include the US Colored Troops sample of black veterans to analyze racial differences in the effect of malaria exposure on lifespan. Exposure to malaria did not lead to a shorter lifespan among black veterans. Evidence suggests that genetic immunity to malaria in black veterans might contribute this heterogeneity.

Evaluation of the precision of the Plasmodium knowlesi growth inhibition assay for Plasmodium vivax Duffy-binding protein-based malaria vaccine development

Recent data indicate increasing disease burden and importance of Plasmodium vivax (Pv) malaria. A robust assay will be essential for blood-stage Pv vaccine development. Results of the in vitro growth inhibition assay (GIA) with transgenic P. knowlesi (Pk) parasites expressing the Pv Duffy-binding protein region II (PvDBPII) correlate with in vivo protection in the first PvDBPII controlled human malaria infection (CHMI) trials, making the PkGIA an ideal selection tool once the precision of the assay is defined. To determine the precision in percentage of inhibition in GIA (%GIA) and in GIA50 (antibody concentration that gave 50 %GIA), ten GIAs with transgenic Pk parasites were conducted with four different anti-PvDBPII human monoclonal antibodies (mAbs) at concentrations of 0.016 to 2 mg/mL, and three GIAs with eighty anti-PvDBPII human polyclonal antibodies (pAbs) at 10 mg/mL. A significant assay-to-assay variation was observed, and the analysis revealed a standard deviation (SD) of 13.1 in the mAb and 5.94 in the pAb dataset for %GIA, with a LogGIA50 SD of 0.299 (for mAbs). Moreover, the ninety-five percent confidence interval (95 %CI) for %GIA or GIA50 in repeat assays was calculated in this investigation. The error range determined in this study will help researchers to compare PkGIA results from different assays and studies appropriately, thus supporting the development of future blood-stage malaria vaccine candidates, specifically second-generation PvDBPII-based formulations.

Plasmodium vivax tryptophan-rich antigen reduces type I collagen secretion via the NF-κBp65 pathway in splenic fibroblasts

BACKGROUND

The spleen plays a critical role in the immune response against malaria parasite infection, where splenic fibroblasts (SFs) are abundantly present and contribute to immune function by secreting type I collagen (collagen I). The protein family is characterized by Plasmodium vivax tryptophan-rich antigens (PvTRAgs), comprising 40 members. PvTRAg23 has been reported to bind to human SFs (HSFs) and affect collagen I levels. Given the role of type I collagen in splenic immune function, it is important to investigate the functions of the other members within the PvTRAg protein family.

METHODS

Protein structural prediction was conducted utilizing bioinformatics analysis tools and software. A total of 23 PvTRAgs were successfully expressed and purified using an Escherichia coli prokaryotic expression system, and the purified proteins were used for co-culture with HSFs. The collagen I levels and collagen-related signaling pathway protein levels were detected by immunoblotting, and the relative expression levels of inflammatory factors were determined by quantitative real-time PCR.

RESULTS

In silico analysis showed that P. vivax has 40 genes encoding the TRAg family. The C-terminal region of all PvTRAgs is characterized by the presence of a domain rich in tryptophan residues. A total of 23 recombinant PvTRAgs were successfully expressed and purified. Only five PvTRAgs (PvTRAg5, PvTRAg16, PvTRAg23, PvTRAg30, and PvTRAg32) mediated the activation of the NF-κBp65 signaling pathway, which resulted in the production of inflammatory molecules and ultimately a significant reduction in collagen I levels in HSFs.

CONCLUSIONS

Our research contributes to the expansion of knowledge regarding the functional role of PvTRAgs, while it also enhances our understanding of the immune evasion mechanisms utilized by parasites.

A two-dose viral-vectored Plasmodium vivax multistage vaccine confers durable protection and transmission-blockade in a pre-clinical study

Among Plasmodium spp. responsible for human malaria, Plasmodium vivax ranks as the second most prevalent and has the widest geographical range; however, vaccine development has lagged behind that of Plasmodium falciparum, the deadliest Plasmodium species. Recently, we developed a multistage vaccine for P. falciparum based on a heterologous prime-boost immunization regimen utilizing the attenuated vaccinia virus strain LC16m8Δ (m8Δ)-prime and adeno-associated virus type 1 (AAV1)-boost, and demonstrated 100% protection and more than 95% transmission-blocking (TB) activity in the mouse model. In this study, we report the feasibility and versatility of this vaccine platform as a P. vivax multistage vaccine, which can provide 100% sterile protection against sporozoite challenge and >95% TB efficacy in the mouse model. Our vaccine comprises m8Δ and AAV1 viral vectors, both harboring the gene encoding two P. vivax circumsporozoite (PvCSP) protein alleles (VK210; PvCSP-Sal and VK247; -PNG) and P25 (Pvs25) expressed as a Pvs25-PvCSP fusion protein. For protective efficacy, the heterologous m8Δ-prime/AAV1-boost immunization regimen showed 100% (short-term; Day 28) and 60% (long-term; Day 242) protection against PvCSP VK210 transgenic Plasmodium berghei sporozoites. For TB efficacy, mouse sera immunized with the vaccine formulation showed >75% TB activity and >95% transmission reduction activity by a direct membrane feeding assay using P. vivax isolates in blood from an infected patient from the Brazilian Amazon region. These findings provide proof-of-concept that the m8Δ/AAV1 vaccine platform is sufficiently versatile for P. vivax vaccine development. Future studies are needed to evaluate the safety, immunogenicity, vaccine efficacy, and synergistic effects on protection and transmission blockade in a non-human primate model for Phase I trials.

Characterisation of Plasmodium vivax lactate dehydrogenase dynamics in P. vivax infections

Plasmodium vivax lactate dehydrogenase (PvLDH) is an essential enzyme in the glycolytic pathway of P. vivax. It is widely used as a diagnostic biomarker and a measure of total-body parasite biomass in vivax malaria. However, the dynamics of PvLDH remains poorly understood. Here, we developed mathematical models that capture parasite and matrix PvLDH dynamics in ex vivo culture and the human host. We estimated key biological parameters characterising in vivo PvLDH dynamics based on longitudinal data of parasitemia and PvLDH concentration collected from P. vivax-infected humans, with the estimates informed by the ex vivo data as prior knowledge in a Bayesian hierarchical framework. We found that the in vivo accumulation rate of intraerythrocytic PvLDH peaks at 10-20 h post-invasion (late ring stage) with a median estimate of intraerythrocytic PvLDH mass at the end of the life cycle to be 9.4 × 10-3ng. We also found that the median estimate of in vivo PvLDH half-life was approximately 21.9 h. Our findings provide a foundation with which to advance our quantitative understanding of P. vivax biology and will facilitate the improvement of PvLDH-based diagnostic tools.

Transmission-reducing and -enhancing monoclonal antibodies against Plasmodium vivax gamete surface protein Pvs48/45

Gamete surface protein P48/45 has been shown to be important for male gamete fertility and a strong candidate for the development of a malaria transmission-blocking vaccine (TBV). However, TBV development for Plasmodium vivax homolog Pvs48/45 has been slow because of a number of challenges: availability of conformationally suitable recombinant protein; the lack of an in vivo challenge model; and the inability to produce P. vivax gametocytes in culture to test transmission-blocking activity of antibodies. To support ongoing efforts to develop Pvs48/45 as a potential vaccine candidate, we initiated efforts to develop much needed reagents to move the field forward. We generated monoclonal antibodies (mAbs) directed against Pvs48/45 and characterized putative functional domains in Pvs48/45 using recombinant fragments corresponding to domains D1-D3 and their biological functionality through ex vivo direct membrane feeding assays (DMFAs) using P. vivax parasites from patients in a field setting in Brazil. While some mAbs partially blocked oocyst development in the DMFA, one mAb caused a significant enhancement of the infectivity of gametocytes in the mosquitoes. Individual mAbs exhibiting blocking and enhancing activities recognized non-overlapping epitopes in Pvs48/45. Further characterization of precise epitopes recognized by transmission-reducing and -enhancing antibodies will be crucial to design an effective immunogen with optimum transmission-reducing potential.

Genetic polymorphisms of Plasmodium vivax ookinete (sexual stage) surface proteins (Pvs25 and Pvs28) from Thailand

Plasmodium vivax is the most geographically widespread malaria parasite in human presently. The ookinete surface proteins of sexual stage of malaria parasites, Pvs25 and Pvs28, are candidates for the transmission blocking vaccine. The antigenic variation in population might be barrier for vaccine development. The objective of this study was to investigate the genetic diversity of Pvs25 and Pvs28 in endemic areas of Thailand. P. vivax clinical isolates collected from Thai-neighboring border areas were analyzed using polymerase chain reaction and sequencing method. Three and 14 amino acid substitutions were observed in 43 Pvs25 and 48 Pvs28 sequences, respectively. Three haplotypes in Pvs25 and 14 haplotypes with 5-7 GSGGE/D tandem repeats in Pvs28 were identified. The nucleotide diversity of pvs25 (π = 0.00059) had lower level than pvs28 (π = 0.00517). Tajima's D value for both pvs25 and pvs28 genes were negative while no significant difference was found (P > 0.10). Low genetic diversity was found in pvs25 and pvs28 genes in Thailand. The finding of the most frequent amino acid substitutions was consistent with global isolates. Therefore, the data could be helpful in developing of effective transmission blocking vaccine in malaria endemic areas.

Mathematical models of Plasmodium vivax transmission: A scoping review

Plasmodium vivax is one of the most geographically widespread malaria parasites in the world, primarily found across South-East Asia, Latin America, and parts of Africa. One of the significant characteristics of the P. vivax parasite is its ability to remain dormant in the human liver as hypnozoites and subsequently reactivate after the initial infection (i.e. relapse infections). Mathematical modelling approaches have been widely applied to understand P. vivax dynamics and predict the impact of intervention outcomes. Models that capture P. vivax dynamics differ from those that capture P. falciparum dynamics, as they must account for relapses caused by the activation of hypnozoites. In this article, we provide a scoping review of mathematical models that capture P. vivax transmission dynamics published between January 1988 and May 2023. The primary objective of this work is to provide a comprehensive summary of the mathematical models and techniques used to model P. vivax dynamics. In doing so, we aim to assist researchers working on mathematical epidemiology, disease transmission, and other aspects of P. vivax malaria by highlighting best practices in currently published models and highlighting where further model development is required. We categorise P. vivax models according to whether a deterministic or agent-based approach was used. We provide an overview of the different strategies used to incorporate the parasite's biology, use of multiple scales (within-host and population-level), superinfection, immunity, and treatment interventions. In most of the published literature, the rationale for different modelling approaches was driven by the research question at hand. Some models focus on the parasites' complicated biology, while others incorporate simplified assumptions to avoid model complexity. Overall, the existing literature on mathematical models for P. vivax encompasses various aspects of the parasite's dynamics. We recommend that future research should focus on refining how key aspects of P. vivax dynamics are modelled, including spatial heterogeneity in exposure risk and heterogeneity in susceptibility to infection, the accumulation of hypnozoite variation, the interaction between P. falciparum and P. vivax, acquisition of immunity, and recovery under superinfection.

Genetic differentiation of Plasmodium vivax duffy binding protein in Ethiopia and comparison with other geographical isolates

BACKGROUND

Plasmodium vivax Duffy binding protein (PvDBP) is a merozoite surface protein located in the micronemes of P. vivax. The invasion of human reticulocytes by P. vivax merozoites depends on the parasite DBP binding domain engaging Duffy Antigen Receptor for Chemokine (DARC) on these red blood cells (RBCs). PvDBPII shows high genetic diversity which is a major challenge to its use in the development of a vaccine against vivax malaria.

METHODS

A cross-sectional study was conducted from February 2021 to September 2022 in five study sites across Ethiopia. A total of 58 blood samples confirmed positive for P. vivax by polymerase chain reaction (PCR) were included in the study to determine PvDBPII genetic diversity. PvDBPII were amplified using primers designed from reference sequence of P. vivax Sal I strain. Assembling of sequences was done using Geneious Prime version 2023.2.1. Alignment and phylogenetic tree constructions using MEGA version 10.1.1. Nucleotide diversity and haplotype diversity were analysed using DnaSP version 6.12.03, and haplotype network was generated with PopART version 1.7.

RESULTS

The mean age of the participants was 25 years, 5 (8.6%) participants were Duffy negatives. From the 58 PvDBPII sequences, seven haplotypes based on nucleotide differences at 8 positions were identified. Nucleotide diversity and haplotype diversity were 0.00267 ± 0.00023 and 0.731 ± 0.036, respectively. Among the five study sites, the highest numbers of haplotypes were identified in Arbaminch with six different haplotypes while only two haplotypes were identified in Gambella. The phylogenetic tree based on PvDBPII revealed that parasites of different study sites shared similar genetic clusters with few exceptions. Globally, a total of 39 haplotypes were identified from 223 PvDBPII sequences representing different geographical isolates obtained from NCBI archive. The nucleotide and haplotype diversity were 0.00373 and 0.845 ± 0.015, respectively. The haplotype prevalence ranged from 0.45% to 27.3%. Two haplotypes were shared among isolates from all geographical areas of the globe.

CONCLUSIONS

PvDBPII of the Ethiopian P. vivax isolates showed low nucleotide but high haplotype diversity, this pattern of genetic variability suggests that the population may have undergone a recent expansion. Among the Ethiopian P. vivax isolates, almost half of the sequences were identical to the Sal-I reference sequence. However, there were unique haplotypes observed in the Ethiopian isolates, which does not share with isolates from other geographical areas. There were two haplotypes that were common among populations across the globe. Categorizing population haplotype frequency can help to determine common haplotypes for designing an effective blood-stage vaccine which will have a significant role for the control and elimination of P. vivax.

PvDBPII elicits multiple antibody-mediated mechanisms that reduce growth in a Plasmodium vivax challenge trial

The receptor-binding domain, region II, of the Plasmodium vivax Duffy binding protein (PvDBPII) binds the Duffy antigen on the reticulocyte surface to mediate invasion. A heterologous vaccine challenge trial recently showed that a delayed dosing regimen with recombinant PvDBPII SalI variant formulated with adjuvant Matrix-MTM reduced the in vivo parasite multiplication rate (PMR) in immunized volunteers challenged with the Thai P. vivax isolate PvW1. Here, we describe extensive analysis of the polyfunctional antibody responses elicited by PvDBPII immunization and identify immune correlates for PMR reduction. A classification algorithm identified antibody features that significantly contribute to PMR reduction. These included antibody titre, receptor-binding inhibitory titre, dissociation constant of the PvDBPII-antibody interaction, complement C1q and Fc gamma receptor binding and specific IgG subclasses. These data suggest that multiple immune mechanisms elicited by PvDBPII immunization are likely to be associated with protection and the immune correlates identified could guide the development of an effective vaccine for P. vivax malaria. Importantly, all the polyfunctional antibody features that correlated with protection cross-reacted with both PvDBPII SalI and PvW1 variants, suggesting that immunization with PvDBPII should protect against diverse P. vivax isolates.

An imported malaria case with repeated episodes of neurological syndromes resulting from different Plasmodium species

BACKGROUND

Imported cerebral malaria (CM) cases in non-endemic areas are often misdiagnosed, which delays treatment. Post-malaria neurological syndrome (PMNS) after recovery from severe malaria can also complicate diagnosis.

CASE

We report an imported malaria case from West Africa with two sequential episodes with neurological syndromes within about a month. The first episode was diagnosed as CM with microscopy-positive Plasmodium falciparum infection. The second episode, occurring a month after the recovery from the first CM episode, was consistent with PMNS, since malaria parasites were not detected by microscopy in peripheral blood smears. However, this diagnosis was complicated by the detection of Plasmodium vivax in peripheral blood by PCR, suggesting a potential cause of the second episode by P. vivax.

CONCLUSION

This study suggests that PMNS often occurs after severe falciparum malaria. Concurrent P. vivax infection with pathogenic biomass being predominantly extravascular further complicates accurate diagnosis.

Plasmodium vivax Malaria and G6PD Testing

Early malaria investigators were certainly correct in classifying the species falciparum and the species vivax as belonging to the same genus, Plasmodium [...].

Designing an effective malaria vaccine targeting Plasmodium vivax Duffy-binding protein

Malaria caused by the Plasmodium vivax parasite is a major global health burden. Immunity against blood-stage infection reduces parasitemia and disease severity. Duffy-binding protein (DBP) is the primary parasite protein responsible for the invasion of red blood cells and it is a leading subunit vaccine candidate. An effective vaccine, however, is still lacking despite decades of interest in DBP as a vaccine candidate. This review discusses the reasons for targeting DBP, the challenges associated with developing a vaccine, and modern structural vaccinology methods that could be used to create an effective DBP vaccine. Next-generation DBP vaccines have the potential to elicit a broadly protective immune response and provide durable and potent protection from P. vivax malaria.

Plasmodium vivax Malaria in Duffy-Positive Patients in Rwanda

Plasmodium vivax is the second-most common malaria pathogen globally, but is considered very rare in the predominantly Duffy-negative sub-Saharan African population. In 259 malaria patients from highland southern Rwanda, we assessed Plasmodium species and Duffy blood group status by polymerase chain reaction (PCR). Plasmodium falciparum, P. vivax, Plasmodium malariae, and Plasmodium ovale were seen in 90.7%, 8.1%, 11.6%, and 5.0%, respectively. Plasmodium vivax occurred more frequently as a monoinfection than in combination with P. falciparum. All P. vivax-infected individuals showed heterozygous Duffy positivity, whereas this was the case for only 3.1% of patients with P. falciparum monoinfection and malaria-negative control subjects (P < 0.01). Based on PCR diagnosis, P. vivax is not rare in southern Rwanda. All episodes of P. vivax were observed in heterozygous Duffy-positive patients, whereas elsewhere in Africa, P. vivax is also reported in Duffy-negative individuals. Refined mapping of Plasmodium species is required to establish control and elimination strategies including all malaria species.

Preliminary characterization of Plasmodium vivax sporozoite antigens as pre-erythrocytic vaccine candidates

Plasmodium vivax pre-erythrocytic (PE) vaccine research has lagged far behind efforts to develop Plasmodium falciparum vaccines. There is a critical gap in our knowledge of PE antigen targets that can induce functionally inhibitory neutralizing antibody responses. To overcome this gap and guide the selection of potential PE vaccine candidates, we considered key characteristics such as surface exposure, essentiality to infectivity and liver stage development, expression as recombinant proteins, and functional immunogenicity. Selected P. vivax sporozoite antigens were surface sporozoite protein 3 (SSP3), sporozoite microneme protein essential for cell traversal (SPECT1), sporozoite surface protein essential for liver-stage development (SPELD), and M2 domain of MAEBL. Sequence analysis revealed little variation occurred in putative B-cell and T-cell epitopes of the PE candidates. Each antigen was tested for expression as refolded recombinant proteins using an established bacterial expression platform and only SPELD failed. The successfully expressed antigens were immunogenic in vaccinated laboratory mice and were positively reactive with serum antibodies of P. vivax-exposed residents living in an endemic region in Thailand. Vaccine immune antisera were tested for reactivity to native sporozoite proteins and for their potential vaccine efficacy using an in vitro inhibition of liver stage development assay in primary human hepatocytes quantified on day 6 post-infection by high content imaging analysis. The anti-PE sera produced significant inhibition of P. vivax sporozoite invasion and liver stage development. This report provides an initial characterization of potential new PE candidates for a future P. vivax vaccine.

Transfection Models to Investigate Plasmodium vivax-Type Dormant Liver Stage Parasites

Plasmodium vivax causes the second highest number of malaria morbidity and mortality cases in humans. Several biological traits of this parasite species, including the formation of dormant stages (hypnozoites) that persist inside the liver for prolonged periods of time, present an obstacle for intervention measures and create a barrier for the elimination of malaria. Research into the biology of hypnozoites requires efficient systems for parasite transmission, liver stage cultivation and genetic modification. However, P. vivax research is hampered by the lack of an in vitro blood stage culture system, rendering it reliant on in vivo-derived, mainly patient, material for transmission and liver stage culture. This has also resulted in limited capability for genetic modification, creating a bottleneck in investigations into the mechanisms underlying the persistence of the parasite inside the liver. This bottleneck can be overcome through optimal use of the closely related and experimentally more amenable nonhuman primate (NHP) parasite, Plasmodium cynomolgi, as a model system. In this review, we discuss the genetic modification tools and liver stage cultivation platforms available for studying P. vivax persistent stages and highlight how their combined use may advance our understanding of hypnozoite biology.

Determination of different social groups' level of knowledge about malaria in a multicultural Amazonian cross-border context

BACKGROUND

A steady decline in the number of cases of malaria was observed in the 2000s in French Guiana. This enabled regional health policies to shift their public health goal from control to elimination. To include inhabitants in this strategy, the main objective of this study was to describe knowledge about malaria, and related attitudes and practices in persons living in the French Guiana border.

METHODS

We conducted a survey in people over 15 years old living in the twelve neighbourhoods of Saint-Georges de l'Oyapock with the highest malaria incidence. It comprised a 147-item questionnaire which collected data on socio-demographic characteristics and included a Knowledge Attitude and Practices survey on malaria. Knowledge-related data were studied using exploratory statistical methods to derive summary variables. A binary variable assessing level of knowledge was proposed and then assessed using exploratory approaches.

RESULTS

The mean age of the 844 participants was 37.2 years [15.8], the male/female sex ratio was 0.8. In terms of nationality, 485 (57.5%) participants were Brazilian and 352 (41.7%) French. One third (305, 36.1%) spoke Brazilian Portuguese as their native language, 295 (34.9%) the Amerindian language Palikur, 36 (4.3%) French. The symptoms of malaria and prevention means were poorly known by 213 (25.2%) and 378 (44.8%) respondents, respectively. A quarter (206, 24.4%) did not know that malaria can be fatal. Overall, 251 people (29.7%) had an overall poor level of knowledge about malaria. Being under 25 years old, living in a native Amerindian neighbourhood, having an Amerindian mother tongue language, having risk behaviours related to gold mining were significantly associated with a poor level of knowledge.

CONCLUSIONS

This study is the first to describe the poor level of knowledge about malaria in populations living in the malaria endemic border area along the Oyapock river in French Guiana. Results will allow to reinforce, to diversify and to culturally adapt prevention messages and health promotion to increase their effectiveness with a view to quickly reaching the goal of malaria elimination through empowerment.

Molecular detection of human Plasmodium species using a multiplex real time PCR

Molecular detection methods have revealed higher sensitivity and specificity than conventional microscopy or rapid diagnostic tests for malaria diagnosis. In this study, we implemented, evaluated and validated according to the ISO 15,189 requirements, a multiplex real-time PCR assay to detect and identify the five human malaria parasites. DNA samples were extracted from whole blood or dried blood spots drawn from patients. Based on the External Quality Assessment (whole blood), this method shows 100% sensitivity and specificity. This PCR detected P. vivax up to 0.25 p/µl, P. falciparum and P. knowlesi up to 0.5 p/µl, P. ovale up to 1 p/µl and P. malariae up to 5 p/µl of blood. From blood spots (extraction from four punches), it detected P. vivax at 5 p/µl, P. falciparum, P. ovale and P. knowlesi at 20 p/µl and P. malariae at 125 p/µl. In conclusion, this quantitative PCR shows excellent performance, is easy to use and DNA saver. It is especially useful to actively screen large population groups and identify the five human malaria parasites in a context of low malaria transmission.

Significant number of Plasmodium vivax mono-infections by PCR misidentified as mixed infections (P. vivax/P. falciparum) by microscopy and rapid diagnostic tests: malaria diagnostic challenges in Ethiopia

BACKGROUND

Plasmodium vivax malaria is now recognized as a cause of severe morbidity and mortality, resulting in a substantial negative effect on health especially in endemic countries. Accurate and prompt diagnosis and treatment of P. vivax malaria is vital for the control and elimination of the disease.

METHODS

A cross-sectional study was conducted from February 2021 to September 2022 at five malaria endemic sites in Ethiopia including Aribaminch, Shewarobit, Metehara, Gambella, and Dubti. A total of 365 samples that were diagnosed positive for P. vivax (mono and mixed infection) using RDT, site level microscopists and expert microscopists were selected for PCR. Statistical analyses were performed to calculate the proportions, agreement (k), frequencies, and ranges among different diagnostic methods. Fisher's exact tests and correlation test were used to detect associations and relationship between different variables.

RESULTS

Of the 365 samples, 324 (88.8%), 37(10.1%), 2 (0.5%), and 2 (0.5%) were P. vivax (mono), P. vivax/Plasmodium falciparum (mixed), P. falciparum (mono) and negative by PCR, respectively. The overall agreement of rapid diagnostic test (RDT), site level microscopy and expert microscopists result with PCR was 90.41% (k: 0.49), 90.96% (k: 0.53), and 80.27% (k: 0.24). The overall prevalence of sexual (gametocyte) stage P. vivax in the study population was 215/361 (59.6%). The majority of these 215 samples (180; 83.7%) had below 1000 parasites/µl, with only four samples (1.9%) had ≥ 5000 parasites/µl. The gametocyte density was found to be weakly positive but statically significant with asexual parasitaemia (r = 0.31; p < 0.001).

CONCLUSION

Both microscopy and RDT showed moderate agreement with PCR in the detection and identification of P. vivax (mono) and P. vivax/P. falciparum (mixed) infections. Therefore, to achieve malaria elimination goals, strengthening routine malaria diagnostic methods by implementing diagnostic tools with a good performance in detecting and accurately identifying malaria species in clinical settings is recommended.

Potential hidden Plasmodium vivax malaria reservoirs from low parasitemia Duffy-negative Ethiopians: Molecular evidence

BACKGROUND

The interaction between the Plasmodium vivax Duffy-binding protein and the corresponding Duffy Antigen Receptor for Chemokines (DARC) is primarily responsible for the invasion of reticulocytes by P. vivax. The Duffy-negative host phenotype, highly prevalent in sub-Saharan Africa, is caused by a single point mutation in the GATA-1 transcription factor binding site of the DARC gene promoter. The aim of this study was to assess the Duffy status of patients with P. vivax infection from different study sites in Ethiopia.

METHODS

A cross-sectional study was conducted from February 2021 to September 2022 at five varying eco-epidemiological malaria endemic sites in Ethiopia. Outpatients who were diagnosed with P. vivax infection (pure and mixed P. vivax/P. falciparum) by microscopy and Rapid Diagnostic Test (RDT) were subjected to PCR genotyping at the DARC promoter. The associations between P. vivax infection, host genotypes and other factors were evaluated.

RESULT

In total, 361 patients with P. vivax infection were included in the study. Patients with pure P. vivax infections accounted for 89.8% (324/361), while the remaining 10.2% (37/361) had mixed P. vivax/P. falciparum infections. About 95.6% (345/361) of the participants were Duffy-positives (21.2% homozygous and 78.8%, heterozygous) and 4.4% (16/361) were Duffy-negatives. The mean asexual parasite density in homozygous and heterozygous Duffy-positives was 12,165 p/μl (IQR25-75: 1,640-24,234 p/μl) and11,655 p/μl (IQR25-75: 1,676-14,065 p/μl), respectively, significantly higher than that in Duffy-negatives (1,227p/μl; IQR25-75: 539-1,732p/μl).

CONCLUSION

This study confirms that Duffy-negativity does not provide complete protection against P. vivax infection. The development of P. vivax-specific elimination strategies, including alternative antimalarial vaccines should be facilitated by a better understanding of the epidemiological landscape of vivax malaria in Africa. More importantly, low parasitemia associated with P. vivax infections in Duffy-negative patients may represent hidden reservoirs of transmission in Ethiopia.

Course of Plasmodium infection studied using 2D-COS on human erythrocytes

BACKGROUND

The threat of malaria is still present in the world. Recognizing the type of parasite is important in determining a treatment plan. The golden routine involves microscopic diagnostics of Giemsa-stained thin blood smears, however, alternative methods are also constantly being sought, in order to gain an additional insight into the course of the disease. Spectroscopic methods, e.g., Raman spectroscopy, are becoming increasingly popular, due to the non-destructive nature of these techniques.

METHODS

The study included patients hospitalized for malaria caused by Plasmodium falciparum or Plasmodium vivax, in the Department of Infectious Diseases at the University Hospital in Krakow, Poland, as well as healthy volunteers. The aim of this study was to assess the possibility of using Raman spectroscopy and 2D correlation (2D-COS) spectroscopy in understanding the structural changes in erythrocytes depending on the type of attacking parasite. EPR spectroscopy and two-trace two-dimensional (2T2D) correlation was also used to examine the specificity of paramagnetic centres found in the infected human blood.

RESULTS

Two-dimensional (2D) correlation spectroscopy facilitates the identification of the hidden relationship, allowing for the discrimination of Raman spectra obtained during the course of disease in human red blood cells, infected by P. falciparum or P. vivax. Synchronous cross-peaks indicate the processes taking place inside the erythrocyte during the export of the parasite protein towards the cell membrane. In contrast, moieties that generate asynchronous 2D cross-peaks are characteristic of the respective ligand-receptor domains. These changes observed during the course of the infection, have different dynamics for P. falciparum and P. vivax, as indicated by the asynchronous correlation cross-peaks. Two-trace two-dimensional (2T2D) spectroscopy, applied to EPR spectra of blood at the beginning of the infection, showed differences between P. falciparum and P. vivax.

CONCLUSIONS

A unique feature of 2D-COS is the ability to discriminate the collected Raman and EPR spectra. The changes observed during the course of a malaria infection have different dynamics for P. falciparum and P. vivax, indicated by the reverse sequence of events. For each type of parasite, a specific recycling process for iron was observed in the infected blood.

Plasmodium vivax Presenting With Septic Shock and Disseminated Intravascular Coagulation (DIC): A Case Report

Malaria has various causative agents that can have a spectrum of disease manifestations, some potentially fatal. Various species have been established as etiologies of malaria, though our understanding of the severity of various species is changing. We present a unique case of Plasmodium vivax malaria that resulted in severe disease, a magnitude rarely seen in previous literature. Our patient was a 35-year-old healthy woman who presented to the emergency department with abdominal pain, nausea, vomiting, and fever. Further workup revealed severe thrombocytopenia with prolonged prothrombin (PT) and partial thromboplastin time (PTT). An initial thick smear failed to detect any Plasmodium species, but a thin smear revealed P. vivax. The patient's hospital stay was complicated by septic shock requiring intensive care unit (ICU) admission. This unique case represents P. vivax as the causative agent of severe malaria even in healthy, immunocompetent patients.

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.

Malaria vaccines: the 60-year journey of hope and final success-lessons learned and future prospects

BACKGROUND

The world has made great strides towards beating malaria, although about half of the world population is still exposed to the risk of contracting malaria. Developing an effective malaria vaccine was a huge challenge for medical science. In 2021 the World Health Organization (WHO) approved the first malaria vaccine, RTS,S/AS01 vaccine (Mosquirix™), for widespread use. This review highlights the history of development, and the different approaches and types of malaria vaccines, and the literature to date. It covers the developmental stages of RTS,S/AS01 and recommends steps for its deployment. The review explores other potential vaccine candidates and their status, and suggests options for their further development. It also recommends future roles for vaccines in eradicating malaria. Questions remain on how RTS,S vaccine will work in widespread use and how it can best be utilized to benefit vulnerable communities.

CONCLUSION

Malaria vaccines have been in development for almost 60 years. The RTS,S/AS01 vaccine has now been approved, but cannot be a stand-alone solution. Development should continue on promising candidates such as R21, PfSPZ and P. vivax vaccines. Multi-component vaccines may be a useful addition to other malaria control techniques in achieving eradication of malaria.

Molecular epidemiology of potential candidate markers for chloroquine resistance in imported Plasmodium vivax malaria cases in Iran

BACKGROUND

The spread of Plasmodium vivax strains resistant to chloroquine (CQ) has posed a challenge to control strategies aimed at eliminating malaria. Molecular analysis of candidate resistance markers is very important for monitoring the P. vivax resistance to CQ in different endemic regions. In the present study, the multidrug resistance 1 (pvmdr1) gene, a possible marker for CQ resistance in P. vivax, was evaluated by molecular methods.

METHODS

A simple PCR-RFLP method was developed for mutation analysis in pvmdr1 gene. A number of 120 blood spots were obtained from patients with P. vivax mono-infection in 2021. All of the samples were collected from Pakistani patients who travelled to Iran.

RESULTS

None of the samples had any mutation at codon 976 of pvmdr1, while the 1076 mutation was detected in 96.2% of the examined isolates. Only two pvmdr1 haplotypes were identified, including the single mutant (Y976/1076L) as the most prevalent haplotype (with 96.2% frequency) and the wild type (Y976/F1076; with 3.8% frequency).

CONCLUSIONS

In this study, the major CQ resistance-mediating mutation and multiple mutant haplotypes of the pvmdr1 gene was not detected. However, continuous monitoring of drug resistance markers and close supervision of the efficacy of CQ is essential to detect the potential emergence of CQ-resistant P. vivax isolates in Iran. This data is important for performing future epidemiological surveillance to monitor CQ resistance in this endemic area and the bordering regions.

Changing epidemiology of Plasmodium vivax malaria in Nouakchott, Mauritania: a six-year (2015-2020) prospective study

BACKGROUND

Plasmodium vivax malaria is one of the major infectious diseases of public health concern in Nouakchott, the capital city of Mauritania and the biggest urban setting in the Sahara. The assessment of the current trends in malaria epidemiology is primordial in understanding the dynamics of its transmission and developing an effective control strategy.

METHODS

A 6 year (2015-2020) prospective study was carried out in Nouakchott. Febrile outpatients with a clinical suspicion of malaria presenting spontaneously at Teyarett Health Centre or the paediatric department of Mother and Children Hospital Centre were screened for malaria using a rapid diagnostic test, microscopic examination of Giemsa-stained blood films, and nested polymerase chain reaction. Data were analysed using Microsoft Excel and GraphPad Prism and InStat software.

RESULTS

Of 1760 febrile patients included in this study, 274 (15.5%) were malaria-positive by rapid diagnostic test, 256 (14.5%) were malaria-positive by microscopy, and 291 (16.5%) were malaria-positive by PCR. Plasmodium vivax accounted for 216 of 291 (74.2%) PCR-positive patients; 47 (16.1%) and 28 (9.6%) had P. falciparum monoinfection or P. vivax-P. falciparum mixed infection, respectively. During the study period, the annual prevalence of malaria declined from 29.2% in 2015 to 13.2% in 2019 and 2.1% in 2020 (P < 0.05). Malaria transmission was essentially seasonal, with a peak occurring soon after the rainy season (October-November), and P. vivax infections, but not P. falciparum infections, occurred at low levels during the rest of the year. The most affected subset of patient population was adult male white and black Moors. The decline in malaria prevalence was correlated with decreasing annual rainfall (r = 0.85; P = 0.03) and was also associated with better management of the potable water supply system. A large majority of included patients did not possess or did not use bed nets.

CONCLUSIONS

Control interventions based on prevention, diagnosis, and treatment should be reinforced in Nouakchott, and P. vivax-specific control measures, including chloroquine and 8-aminoquinolines (primaquine, tafenoquine) for treatment, should be considered to further improve the efficacy of interventions and aim for malaria elimination.

Evaluation of transmission-blocking potential of Pv22 using clinical Plasmodium vivax infections and transgenic Plasmodium berghei

Antigens expressed during the sexual development of malaria parasites are transmission-blocking vaccine (TBV) targets. Pb22, a protein expressed and localized to the plasma membrane of gametes and ookinetes in Plasmodium berghei, is an excellent TBV candidate. Here, we evaluated the TB potential of the Plasmodium vivax ortholog Pv22 using a transgenic P. berghei parasite line and P. vivax clinical isolates. The full-length recombinant Pv22 (rPv22) protein was produced and used to immunize mice and rabbits to obtain antibodies. We generated a transgenic P. berghei line (TrPv22Pb) by inserting the pv22 gene into the pb22 locus and showed that Pv22 expression completely rescued the defects in male gametogenesis of the pb22 deletion parasite. Since Pv22 in the transgenic parasite showed similar expression and localization patterns to Pb22, we used the TrPv22Pb parasite as a surrogate to evaluate the TB potential of Pv22. In mosquito feeding assays, mosquitoes feeding on rPv22-immunized mice infected with TrPv22Pb parasites showed a 49.3-53.3 % reduction in the oocyst density compared to the control group. In vitro assays showed that the rPv22 immune sera significantly inhibited exflagellation and ookinete formation of the TrPv22Pb parasites. In a direct membrane feeding assay using three clinical P. vivax isolates, the rabbit anti-rPv22 antibodies also significantly decreased the oocyst density by 53.7, 30.2, and 26.2 %, respectively. This study demonstrated the feasibility of using transgenic P. berghei parasites expressing P. vivax antigens as a potential tool to evaluate TBV candidates. However, the much weaker TB activity of Pv22 obtained from two complementary assays suggest that Pv22 may not be a promising TBV candidate for P. vivax.

Recent Advances in Imported Malaria Pathogenesis, Diagnosis, and Management

Purpose of Review

Malaria is an important human parasitic disease affecting the population of tropical, subtropical regions as well as travelers to these areas.The purpose of this article is to provide clinicians practicing in non-endemic areas with a comprehensive overview of the recent data on microbiologic and pathophysiologic features of five Plasmodium parasites, clinical presentation of uncomplicated and severe cases, modern diagnostic methods, and treatment of malaria.

Recent Findings

Employment of robust surveillance programs, rapid diagnostic tests, highly active artemisinin-based therapy, and the first malaria vaccine have led to decline in malaria incidence; however, emerging drug resistance, disruptions due to the COVID-19 pandemic, and other socio-economic factors have stalled the progress.

Summary

Clinicians practicing in non-endemic areas such as the United States should consider a diagnosis of malaria in returning travelers presenting with fever, utilize rapid diagnostic tests if available at their practice locations in addition to microscopy, and timely initiate guideline-directed management as delays in treatment can lead to poor clinical outcomes.

Plasmodium vivax in Children: Hidden Burden and Conspicuous Challenges, a Narrative Review

There has been progress towards decreasing malaria prevalence globally; however, Plasmodium vivax has been less responsive to elimination efforts compared with Plasmodium falciparum. P. vivax malaria remains a serious public health concern in regions where it is the dominant species (South and South-East Asia, the Eastern Mediterranean region, and South America) and is increasingly recognized for its contribution to overall morbidity and mortality worldwide. The incidence of P. vivax decreases with increasing age owing to rapidly acquired clinical immunity and there is a disproportionate burden of P. vivax in infants and children, who remain highly vulnerable to severe disease, recurrence, and anemia with associated developmental impacts. Diagnosis is sometimes difficult owing to the sensitivity of diagnostic tests to detect low levels of parasitemia. Additionally, the propensity of P. vivax to relapse following reactivation of dormant hypnozoites in the liver contributes to disease recurrence in infants and children, and potentiates morbidity and transmission. The 8-aminoquinolines, primaquine and tafenoquine, provide radical cure (relapse prevention). However, the risk of hemolysis in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency necessitates testing prior to administration of 8-aminoquinolines, which has limited their uptake. Additional challenges include lack of availability of pediatric dose formulations and problems with adherence to primaquine owing to the length of treatment recommended. A paucity of data and studies specific to pediatric P. vivax malaria impacts the ability to deliver targeted interventions. It is imperative that P. vivax in infants and children be the focus of future research, control initiatives, and anti-malarial drug development.

MiR-451a and let-7i-5p loaded extracellular vesicles attenuate heme-induced inflammation in hiPSC-derived endothelial cells

Hemolysis is associated with many pathologies, including trauma, sepsis, hemorrhagic stroke, malaria, and genetic disorders such as sickle cell disease (SCD). When hemolysis occurs, free-heme drives vascular inflammation, resulting in oxidative tissue damage and cardiometabolic complications. A better understanding of heme clearance and detoxification is essential to preventing sustained tissue damage. Human induced pluripotent stem cell (hiPSC)-derived endothelial cells (hiPSC-ECs) provide a novel source of patient-specific cells and tissues for disease modeling, drug discovery, and regenerative therapeutics. Here we report the use of hiPSC-ECs to elucidate the role of miR-451a and let-7i-5p-loaded extracellular vesicles (EVs, such as exosomes) in the inflammatory response to free-heme as a model for heme-induced inflammation. We provide evidence of a significant correlation between miR-451a and let-7i-5p-loaded circulating exosomes in plasmodium-infected patients with reported clinical benchmarks of malaria-severity (e.g., Hemoglobin (Hb) levels, white blood cell counts). Additionally, we determined that exposure of Plasmodium falciparum (Pf) parasites to EVs, loaded with either miRNA, significantly reduces their counts in vitro. Using hiPSCs derived from individuals with wild-type Hb (HbAA) or homozygous sickle cell mutated Hb (HbSS) genotypes, we demonstrate that heme-treated hiPSC-ECs secreted inflammatory products (cytokines, chemokines and growth factors) into supporting media at concentrations that were similar to that reported in HbAA and HbSS serum. This inflammatory response was attenuated by exposure with miR-451a or let-7i-5p-loaded EVs. We also found a decrease in transcription of ICAM1 and P-Selectin, as well as the secretion of key inflammatory cytokines (e.g., CXCL10, TNF-α, and IFN-γ). Based on these findings, we propose a model in which increased levels of exosomal miR-451a and let-7i-5p in Plasmodium-infected individuals will attenuate inflammatory responses to free-heme and parasite-derived products. As a result, infected erythrocytes will less likely adhere to the endothelium, sequester in brain micro vessels, and reduce vaso-occlusive crises that exacerbate cerebral malaria.

Plasmodium vivax blood stage invasion pathways: Contribution of omics technologies in deciphering molecular and cellular mechanisms

Vivax malaria is an infectious disease caused by Plasmodium vivax, a parasitic protozoan transmitted by female Anopheline mosquitoes. Historically, vivax malaria has often been regarded as a benign self-limiting infection due to the observation of low parasitemia in Duffy-positive patients in endemic transmission areas and the virtual absence of infections in Duffy-negative individuals in Sub Saharan Africa. However, the latest estimates show that the burden of the disease is not decreasing in many countries and cases of vivax infections in Duffy-negative individuals are increasingly reported throughout Africa. This raised questions about the accuracy of diagnostics and the evolution of interactions between humans and parasites. For a long time, our knowledge on P. vivax biology has been hampered due to the limited access to biological material and the lack of robust in vitro culture methods. Consequently, little is currently known about P. vivax blood stage invasion mechanisms. The introduction of omics technologies with novel and accessible techniques such as third generation sequencing and RNA sequencing at single cell level, two-dimensional electrophoresis, liquid chromatography, and mass spectrometry, has progressively improved our understanding of P. vivax genetics, transcripts, and proteins. This review aims to provide broad insights into P. vivax invasion mechanisms generated by genomics, transcriptomics, and proteomics and to illustrate the importance of integrated multi-omics studies.

International Center of Excellence for Malaria Research for South Asia and Broader Malaria Research in India

The Malaria Evolution in South Asia (MESA) International Center of Excellence for Malaria Research (ICEMR) conducted research studies at multiple sites in India to record blood-slide positivity over time, but also to study broader aspects of the disease. From the Southwest of India (Goa) to the Northeast (Assam), the MESA-ICEMR invested in research equipment, operational capacity, and trained personnel to observe frequencies of Plasmodium falciparum and Plasmodium vivax infections, clinical presentations, treatment effectiveness, vector transmission, and reinfections. With Government of India partners, Indian and U.S. academics, and trained researchers on the ground, the MESA-ICEMR team contributes information on malaria in selected parts of India.

Plasmodium pitheci malaria in Bornean orang-utans at a rehabilitation centre in West Kalimantan, Indonesia

BACKGROUND

Plasmodial species naturally infecting orang-utans, Plasmodium pitheci and Plasmodium silvaticum, have been rarely described and reportedly cause relatively benign infections. Orang-utans at Rescue Rehabilitation Centres (RRC) across the orang-utan natural range suffer from malaria illness. However, the species involved and clinical pathology of this illness have not been described in a systematic manner. The objective of the present study was to identify the Plasmodium species infecting orang-utans under our care, define the frequency and character of malaria illness among the infected, and establish criteria for successful diagnosis and treatment.

METHODS

During the period 2017-2021, prospective active surveillance of malaria among 131 orang-utans resident in a forested RRC in West Kalimantan (Indonesia) was conducted. A total of 1783 blood samples were analysed by microscopy and 219 by nucleic acid based (PCR) diagnostic testing. Medical records of inpatient orang-utans at the centre from 2010 to 2016 were also retrospectively analysed for instances of symptomatic malaria.

RESULTS

Active surveillance revealed 89 of 131 orang-utans were positive for malaria at least once between 2017 and 2021 (period prevalence = 68%). During that period, 14 cases (affecting 13 orang-utans) developed clinical malaria (0.027 attacks/orang-utan-year). Three other cases were found to have occurred from 2010-2016. Sick individuals presented predominantly with fever, anaemia, thrombocytopenia, and leukopenia. All had parasitaemias in excess of 4000/μL and as high as 105,000/μL, with severity of illness correlating with parasitaemia. Illness and parasitaemia quickly resolved following administration of artemisinin-combined therapies. High levels of parasitaemia also sometimes occurred in asymptomatic cases, in which case, parasitaemia cleared spontaneously.

CONCLUSIONS

This study demonstrated that P. pitheci very often infected orang-utans at this RRC. In about 14% of infected orang-utans, malaria illness occurred and ranged from moderate to severe in nature. The successful clinical management of acute pitheci malaria is described. Concerns are raised about this infection potentially posing a threat to this endangered species in the wild.

Population genomics in neglected malaria parasites

Malaria elimination includes neglected human malaria parasites Plasmodium vivax, Plasmodium ovale spp., and Plasmodium malariae. Biological features such as association with low-density infection and the formation of hypnozoites responsible for relapse make their elimination challenging. Studies on these parasites rely primarily on clinical samples due to the lack of long-term culture techniques. With improved methods to enrich parasite DNA from clinical samples, whole-genome sequencing of the neglected malaria parasites has gained increasing popularity. Population genomics of more than 2200 P. vivax global isolates has improved our knowledge of parasite biology and host-parasite interactions, identified vaccine targets and potential drug resistance markers, and provided a new way to track parasite migration and introduction and monitor the evolutionary response of local populations to elimination efforts. Here, we review advances in population genomics for neglected malaria parasites, discuss how the rich genomic information is being used to understand parasite biology and epidemiology, and explore opportunities for the applications of malaria genomic data in malaria elimination practice.

A Retrospective Review on Severe Malaria in Colombia, 2007–2020

Background: Knowledge of severe malaria (SM) or complicated malaria is insufficient in all its components. The least known type is the one associated with Plasmodium vivax, compared to that caused by P. falciparum. The aim of this study was to provide a general overview of epidemiological information about the burden of SM, obtained from the National Public Health Surveillance System (SIVIGILA) for the period 2007–2020 in Colombia. Methods: A descriptive, retrospective, and cross-sectional study of secondary information was performed via SIVIGILA. Results: There were 9881 SM cases among 1,060,950 total malaria cases in Colombia in 2007–2020: 9.31 SM cases per 1000 malaria cases. During this period, there were 7145 SM cases due to the following species: Plasmodium vivax, 57.6%; P. falciparum, 38.6%; severe mixed malaria, 3.2%; and P. malariae, 0.6%. The most compromised organ systems are the hematological system (54.9%), the liver (9.1%), the kidneys (4.2%), the lungs (1.9%) and the brain (1.6%). Conclusions: There has been a reduction in malaria incidence in Colombia in the last 10–15 years, but there has also been a strong increase in SM incidence. We suggest emphasizing the prevention of the onset of severe malaria, with the early and accurate diagnosis of plasmodial infection.

Assessment of intestinal and blood protozoan infections among pregnant women visiting ante-natal care at Tafo Hospital, Ghana

Introduction

Intestinal and blood protozoans cause morbidity and mortality in both pregnant women and developing foetuses worldwide. It constitutes a major health problem in many tropical areas in Africa. This study assessed the prevalence of intestinal and blood protozoans’ parasitic load and their risk factors among pregnant women visiting antenatal care at Tafo Hospital, Ghana from November 2016 to January 2017.

Method

A pilot cross-sectional study was conducted among consented pregnant women who visited antenatal care at Tafo Government Hospital, Kumasi Ghana. Structured questionnaires were administered to obtain socio-demographic data, knowledge on protozoan infections, and their risk factors among study participants. A stool sample was obtained from each participant for the microscopic examination of the intestinal protozoa. Venous blood was taken from participants for the detection of Plasmodium and Toxoplasma gondii infections. Wet mount and the faecal protozoan concentrated method were done for the identification of intestinal parasites. Blood films and serological examination for malaria rapid diagnostic tests (RDT) were done for identification of Plasmodium parasites while an Enzyme-linked immunosorbent assay (ELISA) was used for detecting the antibodies of T. gondii among participants. Data were analyzed using statistical packages for the social sciences (SPSS).

Results

The mean age of the study participants was 27.83, and ranges from 18 to 40 years. The majority of the participants (82.2%) had never experienced stillbirth nor spontaneous abortion. Intestinal parasites were found in 36.7% of participants. Giardia lamblia (28.1%), Cryptosporidium parvum (5.3%), and Entamoeba histolytica/dispar (3.3%) were among the intestinal protozoans detected. T. gondii antibodies were detected by high levels of immunoglobulins, resulting in IgG (48.0%) and IgM (11.3%) being found among participants, with 7.3% testing positive for both IgM and IgG. The prevalence of malaria infection among the study participants was 2.7%. The consumption of raw or cooked vegetables had significant influence on their intestinal and blood protozoan infections status (p = 0.004) (OR = 0.32, CI = 0.12–0.86). There was a significant association between Hb levels and malaria (p = 0.014) and that of intestinal protozoans (p = 0.035).

Conclusion

The prevalence of intestinal protozoans and blood protozoans such as T. gondii were high and therefore effective measures should be put in place to reduce the infectivity. Environmental hygiene should be improved and education by relevant agencies should be intensified on the possible transmission of intestinal and blood parasite infections given the possible role of these infections in adverse pregnancy outcomes.

Lessons for improved COVID-19 surveillance from the scale-up of malaria testing strategies

Effective control of infectious diseases is facilitated by informed decisions that require accurate and timely diagnosis of disease. For malaria, improved access to malaria diagnostics has revolutionized malaria control and elimination programmes. However, for COVID-19, diagnosis currently remains largely centralized and puts many low- and middle-income countries (LMICs) at a disadvantage. Malaria and COVID-19 are infectious diseases that share overlapping symptoms. While the strategic responses to disease control for malaria and COVID-19 are dependent on the disease ecologies of each disease, the fundamental need for accurate and timely testing remains paramount to inform accurate responses. This review highlights how the roll-out of rapid diagnostic tests has been fundamental in the fight against malaria, primarily within the Asia Pacific and along the Greater Mekong Subregion. By learning from the successful elements of malaria control programmes, it is clear that improving access to point-of-care testing strategies for COVID-19 will provide a suitable framework for COVID-19 diagnosis in not only the Asia Pacific, but all malarious countries. In malaria-endemic countries, an integrated approach to point-of-care testing for COVID-19 and malaria would provide bi-directional benefits for COVID-19 and malaria control, particularly due to their paralleled likeness of symptoms, infection control strategies and at-risk individuals. This is especially important, as previous disease pandemics have disrupted malaria control infrastructure, resulting in malaria re-emergence and halting elimination progress. Understanding and combining strategies may help to both limit disruptions to malaria control and support COVID-19 control.