| Feng Lu | 5 Articles |
As many countries implement different programs aimed at eliminating malaria, attention should be given to asymptomatic carriers that may interrupt the progress. This was a community-based cross-sectional study conducted in Tanzania from December 2022 to July 2023 within 4 villages from each of the 3 regions, Geita and Kigoma, which are high malaria transmission, and Arusha, which is low transmission. Malaria was diagnosed in asymptomatic individuals aged 1 year and older using the malaria rapid diagnostic test and light microscope. A total of 2,365 of 3,489 (67.9%) participants were enrolled from high-transmission villages. The overall prevalence was 25.5% and 15.8% by malaria rapid diagnostic test and light microscope, respectively. Using the respective tools, the prevalence was significantly higher at 35.6% (confidence interval (CI)=23.6–49.9) and 23.1% (CI=16.2–35.1) in the high-transmission regions (Geita and Kigoma) compared with 2.9% (CI=1.1–3.5) and 1.1% (CI=0.7–1.8) in the low-transmission region (Arusha). Children younger than 15 years and males accounted for the greatest proportion of infections. In the study area, the prevalence of asymptomatic cases was higher than that of reported symptomatic cases in health facilities. We hypothesize that these parasite reservoirs may contribute to the persistence of malaria in the country. Therefore, to achieve comprehensive malaria control in the country, the surveillance and screening of asymptomatic malaria cases are vital.
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Plasmodium vivax reemerged in 1993. It has been sustained for more than 25 years and become one of the important indigenous parasitic diseases in northern and western parts of the Republic of Korea near the demilitarized zone. In particular, relapse is a significant concern for the control of malaria, as short- and long-term incubation periods vary among those infected in Korea. In this study, the prevalence of asymptomatic carriers was examined among residents of high endemic areas of vivax malaria during nonseasonal transmission of mosquitoes. Blood samples from 3 endemic regions in northwestern Korea were evaluated by microscopic examination, rapid diagnostic testing, and nested PCR to identify asymptomatic patients carrying malaria parasites in the community. However, no positive malaria case among residents of endemic areas was detected. Additionally, serological analysis was carried out to measure antibodies against 3 antigenic recombinant proteins of P. vivax, merozoite surface protein 1-19, circumsporozoite surface protein-VK210, and liver-stage antigen (PvLSA-N), by the protein array method. Interestingly, seropositivity of sera between previous exposure and samples without exposure to malaria was significantly higher using the PvLSA-N antigen than the other antigens, suggesting that PvLSA-N can be used as a serological marker to analyze the degree of exposure for malaria transmission in endemic areas. This indicates a very low asymptomatic carrier prevalence during the nonmalaria season in the endemic areas of Korea.
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Plasmodium vivax produces numerous caveola-vesicle complex (CVC) structures beneath the membrane of infected erythrocytes. Recently, a member helical interspersed subtelomeric (PHIST) superfamily protein, PcyPHIST/CVC-8195, was identified as CVCs-associated protein in Plasmodium cynomolgi and essential for survival of this parasite. Very little information has been documented to date about PHIST/CVC-8195 protein in P. vivax. In this study, the recombinant PvPHIST/CVC-8195 N and C termini were expressed, and immunoreactivity was assessed using confirmed vivax malaria patients sera by protein microarray. The subcellular localization of PvPHIST/CVC-8195 N and C termini in blood stage parasites was also determined. The antigenicity of recombinant PvPHIST/CVC-8195 N and C terminal proteins were analyzed by using serum samples from the Republic of Korea. The results showed that immunoreactivities to these proteins had 61% and 43% sensitivity and 96.9% and 93.8% specificity, respectively. The N terminal of PvPHIST/CVC-8195 which contains transmembrane domain and export motif (PEXEL; RxLxE/Q/D) produced CVCs location throughout the erythrocytic-stage parasites. However, no fluorescence was detected with antibodies against C terminal fragment of PvPHIST/CVC-8195. These results suggest that the PvPHIST/CVC-8195 is localized on the CVCs and may be immunogenic in natural infection of P. vivax.
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The study of Plasmodium falciparum intraerythrocytic developmental cycle relies on synchronized parasite cultures. This study aimed to quantitatively evaluate 4 common synchronization methods for the culture of P. falciparum 3D7, incorporating a novel nanomaterial-based tool to
objective ly assess late-stage parasite enrichment. The 4 methods including 5% D-sorbitol, isosmotic Percoll-Sorbitol (60% PS), discontinuous Percoll-Sorbitol gradients (70%–40% PS), and the Plasmion method. Synchronization efficiency was assessed through microscopic examination and flow cytometry. In addition to SYBR Green I as the stain for flow cytometry, we innovatively employed 20 nm polystyrene fluorescent microspheres (PFMs20), which bind to parasites following the production of new permeability pathways, to provide an objective validating the enrichment of mature stages. The binding rate was defined as the ratio of PFMs20 positivity to SYBR Green I positivity. Microscopic examination of Giemsa-stained blood smears served as the gold standard for assessing the stage-specific profiles achieved by each synchronization method. The 4 methods yielded distinct efficiency profiles: 5% D-sorbitol achieved 88.37% ring-stage purity; 60% PS demonstrated high late-stage enrichment with PFMs20 binding rates reaching 87.47%; 70%–40% PS uniquely enabled visible hemozoin-rich layer separation and showed 88.12% binding efficiency in its schizont-enriched fraction; while Plasmion yielded a binding rate of 73.37% in its late-stage fraction. Our results formulate a clear decision matrix for synchronization protocol selection. The sorbitol method is ideal for basic ring-stage studies, Percoll-based gradients support rigorous stage-specific investigations, and the Plasmion method is well-suited for resource-limited settings. This comparative analysis provides preliminary guidelines for synchronization method selection that require validation in diverse laboratory and field contexts.
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