Demographic and socioeconomic obstacles to access to malaria services for Myanmar migrants in Thailand.

BACKGROUND: Typically mobile and vulnerable, migrants face significant barriers to access to routine malaria prevention, diagnostics and treatment, which leads to unchecked malaria transmission, particularly in border regions with a high population displacement. This study aimed to investigate the demographic and socioeconomic obstacles to access to malaria services among Myanmar migrants residing in the Thailand-Myanmar border areas. METHODS: A cross-sectional study was conducted in early 2024 across three districts near the Thailand-Myanmar border. Quantitative data were collected from Myanmar migrants using standardized questionnaires through structured surveys. Data analysis included descriptive statistics and simple and multiple logistic regression models. RESULTS: Out of 300 participants, approximately a quarter (27.3%) reported adequate access to comprehensive malaria services, including prevention, diagnostics, treatment and malaria-related health information. In multiple logistic regression models, factors associated with inadequate access included Myanmar migrants aged over 60 years (aOR: 7.63, 95% CI 1.74-20.58), accompanied by one to three family members (aOR: 3.33, 95% CI 1.06-8.45), earning monthly incomes below 3000 THB (aOR: 5.13, 95% CI 1.38-19.09) and 3000 to 6000 THB (aOR: 3.64, 95% CI 1.06-12.51), belonging to the Karen ethnicity (aOR: 2.13, 95% CI 1.02-3.84), with poor perception toward malaria (aOR: 2.03, 95% CI 1.03-4.01) and with poor preventive and health-seeking practices (aOR: 5.83, 95% CI 2.71-9.55). CONCLUSIONS: A significant proportion of Myanmar migrants encounter demographic and socioeconomic barriers to access to routine malaria services in Thailand. Tailored interventions are required to expand such access, including the recruitment of worksite health volunteers, strengthening the role of ethnic health organizations across the border and collaboration with private sector stakeholders (e.g. farm/company owners) to distribute preventive tools and ensure timely referral of suspected malaria cases to health facilities.

Exploring urinary proteomics and peptidomics biomarkers for the diagnosis of mekong schistosomiasis.

Schistosomiasis caused by Schistosoma mekongi is one of the causative agents of human blood fluke infection in the lower Mekong River. Traditionally, the detection of egg morphology in stool samples has served as the prevailing method for diagnosing Schistosoma infection. Nonetheless, this approach exhibits low sensitivity, particularly in early infection detection. Urine has been extensively studied as a noninvasive clinical sample for diagnosing infectious diseases. Despite this, urine proteomic analysis of S. mekongi infection has been less investigated. This study aimed to characterize proteins and peptides present in mouse urine infected with S. mekongi both before infection and at intervals of 1, 2, 4, and 8 weeks post-infection using mass spectrometry-based proteomics. Proteomics analysis revealed 13 up- and only one down-regulated mouse protein consistently found across all time points. Additionally, two S. mekongi uncharacterized proteins were detected throughout the infection period. Using a peptidomics approach, we consistently identified two peptide sequences corresponding to S. mekongi collagen alpha-1(V) in mouse urine across all time points. These findings highlight the potential of these unique proteins, particularly the S. mekongi uncharacterized proteins and collagen alpha-1(V), as potential biomarkers for early detection of S. mekongi infection. Such insights could significantly advance diagnostic strategies for human Mekong schistosomiasis.

Declining Genetic Polymorphisms of the C-terminus Merozoite Surface Protein-1 Amidst Increased Plasmodium knowlesi Transmission in Thailand.

Recent reports from Thailand reveal a substantial surge in Plasmodium knowlesi cases over the past decade, with a more than eightfold increase in incidence by 2023 compared to 2018. This study investigates temporal changes in genetic polymorphism associated with the escalating transmission of P. knowlesi malaria in Thailand over the past two decades. Twenty-five P. knowlesi samples collected in 2018-2023 were sequenced for the 42-kDa region of pkmsp1 and compared with 24 samples collected in 2000-2009, focusing on nucleotide diversity, natural selection, recombination rate, and population differentiation. Seven unique haplotypes were identified in recent samples, compared to 15 in earlier samples. Nucleotide and haplotype diversities were lower in recent samples (π = 0.016, Hd = 0.817) than in earlier samples (π = 0.018, Hd = 0.942). Significantly higher synonymous substitution rates were observed in both sample sets (dS - dN = 2.77 and 2.43, p < 0.05), indicating purifying selection and reduced genetic diversity over time. Additionally, 8 out of 17 mutation points were located on B-cell epitopes, suggesting an adaptive response by the parasites to evade immune recognition. Population differentiation analysis using the fixation index (Fst) revealed high genetic differentiation between parasite populations in central and southern Thailand or Malaysia. Conversely, the relatively lower Fst value between southern Thailand and Malaysia suggests a closer genetic relationship, possibly reflecting historical gene flow. In conclusion, our findings highlight a decline in genetic diversity and evidence of purifying selection associated with the recently increased incidence of P. knowlesi malaria in Thailand. The minor genetic differentiation between P. knowlesi populations from southern Thailand and Malaysia suggests a shared recent ancestry of these parasites and underscores the need for coordinated efforts between the two countries for the elimination of P. knowlesi.

Effectiveness, Safety, and Acceptability of Primaquine Mass Drug Administration in Low-Endemicity Areas in Southern Thailand: Proof-of-Concept Study.

BACKGROUND: A challenge in achieving the malaria-elimination target in the Greater Mekong Subregion, including Thailand, is the predominance of Plasmodium vivax malaria, which has shown extreme resilience to control measures. OBJECTIVE: This proof-of-concept study aimed to provide evidence for implementing primaquine mass drug administration (pMDA) as a strategy for P. vivax elimination in low-endemicity settings. METHODS: The study employed a mixed-methods trial to thoroughly evaluate the effectiveness, safety, acceptability, and community engagement of pMDA. The quantitative part was designed as a 2-period cluster-crossover randomized controlled trial. The intervention was pMDA augmented to the national prevention and control standards with directly observed treatment (DOT) by village health volunteers. The qualitative part employed in-depth interviews and brainstorming discussions. The study involved 7 clusters in 2 districts of 2 southern provinces in Thailand with persistently low P. vivax transmission. In the quantitative part, 5 cross-sectional blood surveys were conducted in both the pMDA and control groups before and 3 months after pMDA. The effectiveness of pMDA was determined by comparing the proportions of P. vivax infections per 1000 population between the 2 groups, with a multilevel zero-inflated negative binomial model adjusted for cluster and time as covariates and the interaction. The safety data comprised adverse events after drug administration. Thematic content analysis was used to assess the acceptability and engagement of stakeholders. RESULTS: In the pre-pMDA period, the proportions of P. vivax infections in the pMDA (n=1536) and control (n=1577) groups were 13.0 (95% CI 8.2-20.4) and 12.0 (95% CI 7.5-19.1), respectively. At month 3 post-pMDA, these proportions in the pMDA (n=1430) and control (n=1420) groups were 8.4 (95% CI 4.6-15.1) and 5.6 (95% CI 2.6-11.5), respectively. No statistically significant differences were found between the groups. The number of malaria cases reduced in all clusters in both groups, and thus, the impact of pMDA was inconclusive. There were no major safety concerns. Acceptance among the study participants and public health care providers at local and national levels was high, and they believed that pMDA had boosted awareness in the community. CONCLUSIONS: pMDA was associated with high adherence, safety, and tolerability, but it may not significantly impact P. vivax transmission. As this was a proof-of-concept study, we decided not to scale up the intervention with larger clusters and samples. An alternative approach involving a targeted primaquine treatment strategy with primaquine and DOT is currently being implemented. We experienced success regarding effective health care workforces at point-of-care centers, effective collaborations in the community, and commitment from authorities at local and national levels. Our efforts boosted the acceptability of the malaria-elimination initiative. Community engagement is recommended to achieve elimination targets. TRIAL REGISTRATION: Thai Clinical Trials Registry TCTR20190806004; https://www.thaiclinicaltrials.org/show/TCTR20190806004.

Naturally Acquired Transmission-Blocking Immunity Against Different Strains of Plasmodium vivax in a Malaria-Endemic Area in Thailand.

BACKGROUND: Human immunity triggered by natural malaria infections impedes parasite transmission from humans to mosquitoes, leading to interest in transmission-blocking vaccines. However, immunity characteristics, especially strain specificity, remain largely unexplored. We investigated naturally acquired transmission-blocking immunity (TBI) against Plasmodium vivax, a major malaria parasite. METHODS: Using the direct membrane-feeding assay, we assessed TBI in plasma samples and examined the role of antibodies by removing immunoglobulins through protein G/L adsorption before mosquito feeding. Strain specificity was evaluated by conducting a direct membrane-feeding assay with plasma exchange. RESULTS: Blood samples from 47 patients with P vivax were evaluated, with 37 plasma samples successfully infecting mosquitoes. Among these, 26 showed inhibition before immunoglobulin depletion. Despite substantial immunoglobulin removal, 4 samples still exhibited notable inhibition, while 22 had reduced blocking activity. Testing against heterologous strains revealed some plasma samples with broad TBI and others with strain-specific TBI. CONCLUSIONS: Our findings indicate that naturally acquired TBI is mainly mediated by antibodies, with possible contributions from other serum factors. The transmission-blocking activity of plasma samples varied by the tested parasite strain, suggesting single polymorphic or multiple targets for naturally acquired TBI. These observations improve understanding of immunity against P vivax and hold implications for transmission-blocking vaccine development.

A Pvs25 mRNA vaccine induces complete and durable transmission-blocking immunity to Plasmodium vivax.

Plasmodium vivax (P. vivax) is the major malaria parasite outside of Africa and no vaccine is available against it. A vaccine that interrupts parasite transmission (transmission-blocking vaccine, TBV) is considered highly desirable to reduce the spread of P. vivax and to accelerate its elimination. However, the development of a TBV against this pathogen has been hampered by the inability to culture the parasite as well as the low immunogenicity of the vaccines developed to date. Pvs25 is the most advanced TBV antigen candidate for P. vivax. However, in previous phase I clinical trials, TBV vaccines based on Pvs25 yielded low antibody responses or had unacceptable safety profiles. As the nucleoside-modified mRNA-lipid nanoparticle (mRNA-LNP) vaccine platform proved to be safe and effective in humans, we generated and tested mRNA-LNP vaccines encoding several versions of Pvs25 in mice. We found that in a prime-boost vaccination schedule, all Pvs25 mRNA-LNP vaccines elicited robust antigen-specific antibody responses. Furthermore, when compared with a Pvs25 recombinant protein vaccine formulated with Montanide ISA-51 adjuvant, the full-length Pvs25 mRNA-LNP vaccine induced a stronger and longer-lasting functional immunity. Seven months after the second vaccination, vaccine-induced antibodies retained the ability to fully block P. vivax transmission in direct membrane feeding assays, whereas the blocking activity induced by the protein/ISA-51 vaccine dropped significantly. Taken together, we report on mRNA vaccines targeting P. vivax and demonstrate that Pvs25 mRNA-LNP outperformed an adjuvanted Pvs25 protein vaccine suggesting that it is a promising candidate for further testing in non-human primates.

Interventions for promoting patients' adherence to 14-day primaquine treatment in a highly malaria-endemic township in Myanmar: a qualitative study among key stakeholders.

BACKGROUND: Plasmodium vivax malaria is considered a major threat to malaria eradication. The radical cure for P. vivax malaria normally requires a 14-day administration of primaquine (PQ) to clear hypnozoites. However, maintaining adherence to PQ treatment is a significant challenge, particularly in malaria-endemic rural areas. Hence, this study aimed to formulate interventions for promoting patients' commitment to PQ treatment in a highly malaria-endemic township in Myanmar. METHODS: A qualitative study was conducted in Waingmaw Township in northern Myanmar, where P. vivax malaria is highly endemic. Key stakeholders including public health officers and community members participated in focus group discussions (FGDs) and in-depth interviews (IDIs) in September 2022. Data were collected using validated guidelines, translated into English, and visualized through thematic analysis. RESULTS: Responsible individuals from different levels of the Myanmar National Malaria Control Programme participated in the IDIs. Most of them reported being aware of the markedly increasing trend of P. vivax and the possibility of relapse cases, especially among migrants who are lost to follow-up. Workload was a key concern surrounding intervention implementation. The respondents discussed possible interventions, such as implementing directly observed treatment (DOT) by family members, piloting a shorter PQ regimen, expanding the community's malaria volunteer network, and strengthening health education activities using local languages to promote reasonable drug adherence. FGDs among community members revealed that although people were knowledgeable about malaria symptoms, places to seek treatment, and the use of bed nets to prevent mosquito bites, most of them still preferred to be treated by quack doctors and rarely used insecticide-treated nets at worksites. Many often stopped taking the prescribed drugs once the symptoms disappeared. Nevertheless, some respondents requested more bed nets to be distributed and health promotion activities to be conducted. CONCLUSION: In rural areas where human resources are limited, interventions such as implementing family member DOT or shortening PQ regimens should be introduced to enhance the radical cure for the P. vivax infection. Disseminating information about the importance of taking the entire treatment course and emphasizing the burden of relapse is also essential.

Gametocyte prevalence and risk factors of P. falciparum malaria patients admitted at the Hospital for Tropical Diseases, Thailand: a 20-year retrospective study.

BACKGROUND: The incidence of malaria in Thailand has dramatically declined over the past two decades, and the goal is to eliminate malaria by 2025. Despite significant progress, one of the key challenges to malaria elimination are undetected gametocyte carriers. Human migration adds complexity to the malaria situation, as it not only sustains local transmission but also poses the risk of spreading drug-resistant parasites. Currently, no study has assessed the prevalence of gametocytes across multiple years in Plasmodium falciparum malaria patients in Thailand, and the risk factors for gametocyte carriage have not been fully explored. METHODS: Medical records of all P. falciparum malaria patients admitted from January 1, 2001 to December 31, 2020 at the Hospital for Tropical Diseases, Thailand, were retrospectively examined and a total of 1962 records were included for analysis. Both P. falciparum parasites and gametocytes were diagnosed by microscopy. A regression model was used to evaluate predictors of gametocyte carriage. RESULTS: The study demonstrated gametocyte prevalence in low malaria transmission areas. Nine risk factors for gametocyte carriage were identified: age between 15 and 24 years [adjusted odds ratio (aOR) = 1.96, 95% confidence interval (CI) 1.18-3.26], Karen ethnicity (aOR = 2.59, 95% CI 1.56-4.29), preadmission duration of fever > 7 days (aOR = 5.40, 95% CI 3.92-7.41), fever on admission (> 37.5 °C) (aOR = 0.61, 95% CI 0.48-0.77), haemoglobin ≤ 8 g/dL (aOR = 3.32, 95% CI 2.06-5.33), asexual parasite density > 5000-25,000/µL (aOR = 0.71, 95% CI 0.52-0.98), asexual parasite density > 25,000-100,000/µL (aOR = 0.74, 95% CI 0.53-1.03), asexual parasite density > 100,000/µL (aOR = 0.51, 95% CI 0.36-0.72), platelet count ≤ 100,000/µL (aOR = 0.65, 95% CI 0.50-0.85, clinical features of severe malaria (aOR = 2.33, 95% CI 1.76-3.10) and dry season (aOR = 1.41, 95% CI 1.10-1.80). An increasing incidence of imported transnational malaria cases was observed over the past two decades. CONCLUSIONS: This is the first study to determine the prevalence of gametocytes among patients with symptomatic P. falciparum malaria, identify the risk factors for gametocyte carriage, and potential gametocyte carriers in Thailand. Blocking transmission is one of the key strategies for eliminating malaria in these areas. The results might provide important information for targeting gametocyte carriers and improving the allocation of resources for malaria control in Thailand. This study supports the already nationally recommended use of a single dose of primaquine in symptomatic P. falciparum malaria patients to clear gametocytes.

Interventions for promoting patients' adherence to 14-day primaquine treatment in a highly malaria-endemic township in Myanmar: A qualitative study among key stakeholders.

Background: Plasmodium vivax malaria is considered a major threat to malaria eradication. The radical cure for P. vivax malaria normally requires a 14-day administration of primaquine (PQ) to clear hypnozoites. However, maintaining adherence to PQ treatment is a significant challenge, particularly in malaria-endemic rural areas. Hence, this study aimed to formulate interventions for promoting patients' commitment to PQ treatment in a highly malaria-endemic township in Myanmar. Methods: A qualitative study was conducted in Waingmaw Township in northern Myanmar, where P. vivax malaria is highly endemic. Key stakeholders including public health officers and community members participated in focus group discussions (FGDs) and in-depth interviews (IDIs) in September 2022. Data were collected using validated guidelines, translated into English, and visualized through thematic analysis. Results: Responsible individuals from different levels of the Myanmar National Malaria Control Program participated in the IDIs. Most of them reported being aware of the markedly increasing trend of P. vivax and the possibility of relapse cases, especially among migrants who are lost to follow-up. Workload was a key concern surrounding intervention implementation. The respondents discussed possible interventions, such as implementing directly observed treatment (DOT) by family members, piloting a shorter PQ regimen, expanding the community's malaria volunteer network, and strengthening health education activities using local languages to promote reasonable drug adherence. FGDs among community members revealed that although people were knowledgeable about malaria symptoms, places to seek treatment, and the use of bed nets to prevent mosquito bites, most of them still preferred to be treated by quack doctors and rarely used insecticide-treated nets at worksites. Many often stopped taking the prescribed drugs once the symptoms disappeared. Nevertheless, some respondents requested more bed nets to be distributed and health promotion activities to be conducted. Conclusion: In rural areas where human resources are limited, interventions such as implementing family member DOT or shortening PQ regimens should be introduced to enhance the radical cure for the P. vivax infection. Disseminating information about the importance of taking the entire treatment course and emphasizing the burden of relapse is also essential.

Genetic diversity and molecular evolution of Plasmodium vivax Duffy Binding Protein and Merozoite Surface Protein-1 in northwestern Thailand.

The local diversity and population structure of malaria parasites vary across different regions of the world, reflecting variations in transmission intensity, host immunity, and vector species. This study aimed to use amplicon sequencing to investigate the genotypic patterns and population structure of P. vivax isolates from a highly endemic province of Thailand in recent years. Amplicon deep sequencing was performed on 70 samples for the 42-kDa region of pvmsp1 and domain II of pvdbp. Unique haplotypes were identified and a network constructed to illustrate genetic relatedness in northwestern Thailand. Based on this dataset of 70 samples collected between 2015 and 2021, 16 and 40 unique haplotypes were identified in pvdbpII and pvmsp142kDa, respectively. Nucleotide diversity was higher in pvmsp142kDa than in pvdbpII (π = 0.027 and 0.012), as was haplotype diversity (Hd = 0.962 and 0.849). pvmsp142kDa also showed a higher recombination rate and higher levels of genetic differentiation (Fst) in northwestern Thailand versus other regions (0.2761-0.4881). These data together suggested that the genetic diversity of P. vivax in northwestern Thailand at these two studied loci evolved under a balancing selection, most likely host immunity. The lower genetic diversity of pvdbpII may reflect its stronger functional constrain. In addition, despite the balancing selection, a decrease in genetic diversity was observed. Hd of pvdbpII decreased from 0.874 in 2015-2016 to 0.778 in 2018-2021; π of pvmsp142kDa decreased from 0.030 to 0.022 over the same period. Thus, the control activities must have had a strong impact on the parasite population size. The findings from this study provide an understanding of P. vivax population structure and the evolutionary force on vaccine candidates. They also established a new baseline for tracking future changes in P. vivax diversity in the most malarious area of Thailand.

The spatial signature of Plasmodium vivax and Plasmodium falciparum infections: quantifying the clustering of infections in cross-sectional surveys and cohort studies.

BACKGROUND: Over the last decades, enormous successes have been achieved in reducing malaria burden globally. In Latin America, South East Asia, and the Western Pacific, many countries now pursue the goal of malaria elimination by 2030. It is widely acknowledged that Plasmodium spp. infections cluster spatially so that interventions need to be spatially informed, e.g. spatially targeted reactive case detection strategies. Here, the spatial signature method is introduced as a tool to quantify the distance around an index infection within which other infections significantly cluster. METHODS: Data were considered from cross-sectional surveys from Brazil, Thailand, Cambodia, and Solomon Islands, conducted between 2012 and 2018. Household locations were recorded by GPS and finger-prick blood samples from participants were tested for Plasmodium infection by PCR. Cohort studies from Brazil and Thailand with monthly sampling over a year from 2013 until 2014 were also included. The prevalence of PCR-confirmed infections was calculated at increasing distance around index infections (and growing time intervals in the cohort studies). Statistical significance was defined as prevalence outside of a 95%-quantile interval of a bootstrap null distribution after random re-allocation of locations of infections. RESULTS: Prevalence of Plasmodium vivax and Plasmodium falciparum infections was elevated in close proximity around index infections and decreased with distance in most study sites, e.g. from 21.3% at 0 km to the global study prevalence of 6.4% for P. vivax in the Cambodian survey. In the cohort studies, the clustering decreased with longer time windows. The distance from index infections to a 50% reduction of prevalence ranged from 25 m to 3175 m, tending to shorter distances at lower global study prevalence. CONCLUSIONS: The spatial signatures of P. vivax and P. falciparum infections demonstrate spatial clustering across a diverse set of study sites, quantifying the distance within which the clustering occurs. The method offers a novel tool in malaria epidemiology, potentially informing reactive intervention strategies regarding radius choices of operations around detected infections and thus strengthening malaria elimination endeavours.

Concurrent Infection with SARS-CoV-2 and Orientia tsutsugamushi during the COVID-19 Pandemic in the Maldives.

The COVID-19 pandemic was the worst public-health crisis in recent history. The impact of the pandemic in tropical regions was further complicated by other endemic tropical diseases, which can cause concurrent infections along with COVID-19. Here, we describe the clinical course of a patient with concurrent COVID-19 and scrub typhus infection. The patient's de-identified clinical data were retrieved retrospectively. The patient had progressive breathlessness at the time of presentation and was hospitalized for COVID-19. Respiratory examination revealed dyspnea, tachypnea, and coarse crepitations bilaterally over the entire lung field. Oxygenation was impaired, and a PaO2/FiO2 ratio of 229 suggested acute respiratory distress syndrome. Laboratory tests indicated leukocytosis, thrombocytopenia, ferritinemia, hypoalbuminemia, and transaminitis. Upon revaluation for persistent fever, physical examination revealed an eschar in the right antecubital fossa. Serology further confirmed scrub typhus, with IgM and IgG antibody positivity. A remarkable clinical recovery was achieved with doxycycline. The COVID-19 pandemic might have masked endemic tropical diseases. Clinicians working in endemic regions must always consider common tropical diseases that may present as a co-infection, as in our case. Travel and exposure history are critical guides for narrowing down a differential diagnosis. Early diagnosis and treatment can prevent complications.

In vitro transfection efficiencies of T-shaped spermine-based cationic lipids with identical and nonidentical tails under high serum conditions.

T-shaped spermine-based cationic lipids with identical and nonidentical hydrophobic tails having variable carbon lengths (from C10 to C18) were designed and synthesized. These lipids were characterized, and their structure-activity relationships were determined for DNA binding and transfection ability of these compounds when formulated as cationic liposomes. These liposomes were then applied as non-viral vectors to transfect HEK293T, HeLa, PC3, H460, HepG2, and Calu'3 cell lines with plasmid DNA encoding the green fluorescent protein. ST9, ST12 and ST13 with nonidentical tails could deliver DNA into HEK293T cells up to 60% under serum-free conditions. The lipid ST15 bearing nonidentical tails was found to be a potent gene transfer agent under 40% serum conditions in HEK293T and HeLa cells. Besides their low cytotoxicity, these lipoplexes also exhibited greater transfection efficiency than the commercially available transfection agent, Lipofectamine 3000.

Transmission efficiency of Plasmodium vivax at low parasitaemia.

BACKGROUND: Plasmodium vivax is responsible for much of malaria outside Africa. Although most P. vivax infections in endemic areas are asymptomatic and have low parasite densities, they are considered a potentially important source of transmission. Several studies have demonstrated that asymptomatic P. vivax carriers can transmit the parasite to mosquitoes, but the efficiency has not been well quantified. The aim of this study is to determine the relationship between parasite density and mosquito infectivity, particularly at low parasitaemia. METHODS: Membrane feeding assays were performed using serial dilutions of P. vivax-infected blood to define the relationship between parasitaemia and mosquito infectivity. RESULTS: The infection rate (oocyst prevalence) and intensity (oocyst load) were positively correlated with the parasite density in the blood. There was a broad case-to-case variation in parasite infectivity. The geometric mean parasite density yielding a 10% mosquito infection rate was 33 (CI 95 9-120) parasites/µl or 4 (CI 95 1-17) gametocytes/µl. The geometric mean parasite density yielding a 50% mosquito infection rate was 146 (CI 95 36-586) parasites/µl or 13 (CI 95 3-49) gametocytes/µl. CONCLUSION: This study quantified the ability of P. vivax to infect Anopheles dirus at over a broad range of parasite densities. It provides important information about parasite infectivity at low parasitaemia common among asymptomatic P. vivax carriers.

A Fatal Case of Native Valve Endocarditis with Multiple Embolic Phenomena and Invasive Methicillin-Resistant Staphylococcus aureus Bacteremia: A Case Report from the Maldives.

Infective endocarditis (IE) is a life-threatening condition caused by infection within the endocardium of the heart and commonly involves the valves. The subsequent cascading inflammation leads to the appearance of a highly friable thrombus that is large enough to become lodged within the heart chambers. As a result, fever, fatigue, heart murmurs, and embolization phenomena may be seen in patients with IE. Embolization results in the seeding of bacteria and obstruction of circulation, causing cell ischemia. Of concern, bacteria with the potential to gain pan-drug resistance, such as methicillin-resistant Staphylococcus aureus (MRSA), are increasingly being identified as the causative agent of IE in hospitals and among intravenous drug abusers. We retrospectively reviewed de-identified clinical data to summarize the clinical course of a patient with MRSA isolated using an automated blood culture system. At the time of presentation, the patient showed a poor consciousness level, and the calculated Glasgow scale was 10/15. A high-grade fever with circulatory shock indicated an occult infection, and a systolic murmur was observed with peripheral signs of embolization. This case demonstrated the emerging threat of antimicrobial resistance in the community and revealed clinical findings of IE that may be helpful to clinicians for the early recognition of the disease. The management of such cases requires a multi-specialty approach, which is not widely available in small-island developing states such as the Maldives.

Overexpression of hepatocyte EphA2 enhances liver-stage infection by Plasmodium vivax.

The liver is the first destination of malaria parasites in humans. After reaching the liver by the blood stream, Plasmodium sporozoites cross the liver sinusoid epithelium, enter and exit several hepatocytes, and eventually invade a final hepatocyte host cell. At present, the mechanism of hepatocyte invasion is only partially understood, presenting a key research gap with opportunities for the development of new therapeutics. Recently, human EphA2, a membrane-bound receptor tyrosine kinase, was implicated in hepatocyte infection by the human malaria parasite Plasmodium falciparum and the rodent parasite Plasmodium yoelii, but its role is not known for Plasmodium vivax, a major human parasite whose liver infection poses a specific challenge for malaria treatment and elimination. In this study, the role of EphA2 in P. vivax infection was investigated. It was found that surface expression of several recombinant fragments of EphA2 enhanced the parasite infection rate, thus establishing its role in P. vivax infection. Furthermore, a new permanent cell line (EphA2Extra-HC04) expressing the whole extracellular domain of EphA2 was generated. This cell line supports a higher rate of P. vivax infection and is a valuable tool for P. vivax liver-stage research.

Molecular markers of dihydroartemisinin-piperaquine resistance in northwestern Thailand.

BACKGROUND: Dihydroartemisinin-piperaquine (DHA-PPQ) combination therapy is the current first-line treatment for Plasmodium falciparum malaria in Thailand. Since its introduction in 2015, resistance to this drug combination has emerged in the eastern part of the Greater Mekong Subregion including the eastern part of Thailand near Cambodia. This study aimed to assess whether the resistance genotypes have arisen the western part of country. METHODS: Fifty-seven P. falciparum-infected blood samples were collected in Tak province of northwestern Thailand between 2013 and 2019. Resistance to DHA was examined through the single nucleotide polymorphisms (SNPs) of kelch13. PPQ resistance was examined through the copy number plasmepsin-2 and the SNPs of Pfcrt. RESULTS: Among the samples whose kelch13 were successfully sequenced, approximately half (31/55; 56%) had mutation associated with artemisinin resistance, including G533S (23/55; 42%), C580Y (6/55; 11%), and G538V (2/55; 4%). During the study period, G533S mutation appeared and increased from 20% (4/20) in 2014 to 100% (9/9) in 2019. No plasmepsin-2 gene amplification was observed, but one sample (1/54) had the Pfcrt F145I mutation previously implicated in PPQ resistance. CONCLUSIONS: Kelch13 mutation was common in Tak Province in 2013-2019. A new mutation G533S emerged in 2014 and rose to dominance in 2019. PPQ resistance marker Pfcrt F145I was also detected in 2019. Continued surveillance of treatment efficacy and drug resistance markers is warranted.

Multidisciplinary Investigations of Sustained Malaria Transmission in the Greater Mekong Subregion.

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

Malaria Research for Tailored Control and Elimination Strategies in the Greater Mekong Subregion.

The malaria landscape in the Greater Mekong Subregion has experienced drastic changes with the ramp-up of the control efforts, revealing formidable challenges that slowed down the progress toward malaria elimination. Problems such as border malaria and cross-border malaria introduction, multidrug resistance in Plasmodium falciparum, the persistence of Plasmodium vivax, the asymptomatic parasite reservoirs, and insecticide resistance in primary vectors require integrated strategies tailored for individual nations in the region. In recognition of these challenges and the need for research, the Southeast Asian International Center of Excellence for Malaria Research has established a network of researchers and stakeholders and conducted basic and translational research to identify existing and emerging problems and develop new countermeasures. The installation of a comprehensive disease and vector surveillance system at sentinel sites in border areas with the implementation of passive/active case detection and cross-sectional surveys allowed timely detection and management of malaria cases, provided updated knowledge for effective vector control measures, and facilitated the efficacy studies of antimalarials. Incorporating sensitive molecular diagnosis to expose the significance of asymptomatic parasite reservoirs for sustaining transmission helped establish the necessary evidence to guide targeted control to eliminate residual transmission. In addition, this program has developed point-of-care diagnostics to monitor the quality of artemisinin combination therapies, delivering the needed information to the drug regulatory authorities to take measures against falsified and substandard antimalarials. To accelerate malaria elimination, this program has actively engaged with stakeholders of all levels, fostered vertical and horizontal collaborations, and enabled the effective dissemination of research findings.