Displaying publications 1 - 20 of 80 in total

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  1. Chong ETJ, Neoh JWF, Lau TY, Lim YA, Chai HC, Chua KH, et al.
    Malar J, 2020 Oct 22;19(1):377.
    PMID: 33092594 DOI: 10.1186/s12936-020-03451-x
    BACKGROUND: Understanding the genetic diversity of candidate genes for malaria vaccines such as circumsporozoite protein (csp) may enhance the development of vaccines for treating Plasmodium knowlesi. Hence, the aim of this study is to investigate the genetic diversity of non-repeat regions of csp in P. knowlesi from Malaysian Borneo and Peninsular Malaysia.

    METHODS: A total of 46 csp genes were subjected to polymerase chain reaction amplification. The genes were obtained from P. knowlesi isolates collected from different divisions of Sabah, Malaysian Borneo, and Peninsular Malaysia. The targeted gene fragments were cloned into a commercial vector and sequenced, and a phylogenetic tree was constructed while incorporating 168 csp sequences retrieved from the GenBank database. The genetic diversity and natural evolution of the csp sequences were analysed using MEGA6 and DnaSP ver. 5.10.01. A genealogical network of the csp haplotypes was generated using NETWORK ver. 4.6.1.3.

    RESULTS: The phylogenetic analysis revealed indistinguishable clusters of P. knowlesi isolates across different geographic regions, including Malaysian Borneo and Peninsular Malaysia. Nucleotide analysis showed that the csp non-repeat regions of zoonotic P. knowlesi isolates obtained in this study underwent purifying selection with population expansion, which was supported by extensive haplotype sharing observed between humans and macaques. Novel variations were observed in the C-terminal non-repeat region of csp.

    CONCLUSIONS: The csp non-repeat regions are relatively conserved and there is no distinct cluster of P. knowlesi isolates from Malaysian Borneo and Peninsular Malaysia. Distinctive variation data obtained in the C-terminal non-repeat region of csp could be beneficial for the design and development of vaccines to treat P. knowlesi.

    Matched MeSH terms: Plasmodium knowlesi/genetics*
  2. Fong MY, Rashdi SA, Yusof R, Lau YL
    Malar J, 2015;14:91.
    PMID: 25890095 DOI: 10.1186/s12936-015-0610-x
    Plasmodium knowlesi is one of the monkey malaria parasites that can cause human malaria. The Duffy binding protein of P. knowlesi (PkDBPαII) is essential for the parasite's invasion into human and monkey erythrocytes. A previous study on P. knowlesi clinical isolates from Peninsular Malaysia reported high level of genetic diversity in the PkDBPαII. Furthermore, 36 amino acid haplotypes were identified and these haplotypes could be separated into allele group I and allele group II. In the present study, the PkDBPαII of clinical isolates from the Malaysian states of Sarawak and Sabah in North Borneo was investigated, and compared with the PkDBPαII of Peninsular Malaysia isolates.
    Matched MeSH terms: Plasmodium knowlesi/genetics*
  3. Ahmed MA, Lau YL, Quan FS
    Malar J, 2018 Jul 27;17(1):274.
    PMID: 30053885 DOI: 10.1186/s12936-018-2423-1
    BACKGROUND: Plasmodium knowlesi a parasite of the macaques is currently the most common cause of human malaria in Malaysia. The thrombospondin-related adhesive protein (TRAP) gene is pre-erythrocytic stage antigen. It is a well-characterized vaccine candidate in Plasmodium vivax and Plasmodium falciparum, however, no study has been done in the orthologous gene of P. knowlesi. This study investigates nucleotide diversity, haplotypes, natural selection and population differentiation of full-length pktrap genes in clinical samples from Malaysia.

    METHODS: Forty full-length pktrap sequences from clinical isolates of Malaysia along with the reference H-strain were downloaded from published databases. Genetic diversity, polymorphism, haplotype and natural selection were determined using DnaSP 5.10 software. McDonald-Kreitman test was conducted using P. vivax and Plasmodium coatneyi as ortholog sequence in DnaSP 5.10 software. Population genetic differentiation index (FST) of parasite populations was determined using Arlequin v3.5. Phylogenetic relationships between trap ortholog genes were determined using MEGA 5.0 software.

    RESULTS: Comparison of 40 full-length pktrap sequences along with the H-strain identified 74 SNPs (53 non-synonymous and 21 synonymous substitutions) resulting in 29 haplotypes. Analysis of the full-length gene showed that the nucleotide diversity was lower compared to its nearest ortholog pvtrap. Domain-wise analysis indicated that the proline/asparagine rich region had higher nucleotide diversity compared to the von Willebrand factor domain and the thrombospondin-type-1 domain. McDonald-Kreitman test identified that the ratio of the number of nonsynonymous to synonymous polymorphic sites within P. knowlesi was significantly higher than that of the number of nonsynonymous to synonymous fixed sites between P. knowlesi and P. vivax. The von Willebrand factor domain also indicated balancing selection using MK test, however, it did not give significant results when tested with P. coatneyi as an outgroup. Phylogenetic analysis of full-length genes identified three distinct sub-clusters of P. knowlesi, one originating from Peninsular Malaysia and two originating from Malaysian Borneo. High population differentiation values was observed within samples from Peninsular Malaysia and Malaysian Borneo.

    CONCLUSIONS: This study is the first to report on the genetic diversity and natural selection of full-length pktrap. Low level of genetic diversity was found across the full-length gene of pktrap. Balancing selection of the von Willebrand factor domain indicated that TRAP could be a target in inducing immune response against P. knowlesi infections. However, higher number of samples would be necessary to further confirm the findings.

    Matched MeSH terms: Plasmodium knowlesi/genetics*
  4. Saleh Huddin A, Md Yusuf N, Razak MRMA, Ogu Salim N, Hisam S
    Infect Genet Evol, 2019 11;75:103952.
    PMID: 31279818 DOI: 10.1016/j.meegid.2019.103952
    It has been discovered that Plasmodium knowlesi (P. knowlesi) is transmitted from macaque to man. Thus, the aim of the present study was to determine P. knowlesi genetic diversity in both human (n = 147) and long-tailed macaque (n = 26) samples from high- and low-endemicity localities. Genotyping was performed using seven neutral microsatellite loci markers. The size of the alleles, multiplicity of infection (MOI), mean number of alleles (Na), expected heterozygosity (HE), linkage disequilibrium (LD), and genetic differentiation (FST) were determined. In highly endemic P. knowlesi localities, the MOI for human and long-tailed macaque isolates was 1.04 and 1.15, respectively, while the Na was 11.14 and 7.86, respectively. Based on the allele frequency distribution for all loci, and with FST knowlesi endemicity, the MOI for human and long-tailed macaque isolates was 1.05 and 1.11, respectively, while the Na was 6.14 and 2.71, respectively. Further molecular analysis of the allele frequencies indicated that there was a significant genetic differentiation in human P. knowlesi isolates as compared to long-tailed macaque isolates, with a very low fixation index (FST = 0.016, p knowlesi of a single genotype, while long-tailed macaque tend to acquire polyclonal infections, which supports the assumption that there is a higher rate of transmission among long-tailed macaque. Understanding the genetic diversity of P. knowlesi isolates can provide invaluable information for characterising patterns of the population structure and the migration rate of P. knowlesi in peninsular Malaysia.
    Matched MeSH terms: Plasmodium knowlesi/genetics*
  5. Lai MY, Ooi CH, Lau YL
    Am J Trop Med Hyg, 2018 03;98(3):700-703.
    PMID: 29260656 DOI: 10.4269/ajtmh.17-0738
    The aim of this study was to develop a recombinase polymerase amplification (RPA) combined with a lateral flow (LF) strip method for specific diagnosis of Plasmodium knowlesi. With incubation at 37°C, the 18S rRNA gene of P. knowlesi was successfully amplified within 12 minutes. By adding a specifically designed probe to the reaction solution, the amplified RPA product can be visualized on a LF strip. The RPA assay exhibited high sensitivity with limits of detection down to 10 parasites/μL of P. knowlesi. Nonetheless, it was demonstrated that all P. knowlesi (N = 41) and other Plasmodium sp. (N = 25) were positive while negative samples (N = 8) were negative. Therefore, a combination of RPA and LF strip detection is a highly promising approach with the potential to be suitable for use in resource-limited settings.
    Matched MeSH terms: Plasmodium knowlesi/genetics
  6. Loh JP, Gao QH, Lee VJ, Tetteh K, Drakeley C
    Singapore Med J, 2016 Dec;57(12):686-689.
    PMID: 26805667 DOI: 10.11622/smedj.2016016
    INTRODUCTION: Although there have been several phylogenetic studies on Plasmodium knowlesi (P. knowlesi), only cytochrome c oxidase subunit 1 (COX1) gene analysis has shown some geographical differentiation between the isolates of different countries.

    METHODS: Phylogenetic analysis of locally acquired P. knowlesi infections, based on circumsporozoite, small subunit ribosomal ribonucleic acid (SSU rRNA), merozoite surface protein 1 and COX1 gene targets, was performed. The results were compared with the published sequences of regional isolates from Malaysia and Thailand.

    RESULTS: Phylogenetic analysis of the circumsporozoite, SSU rRNA and merozoite surface protein 1 gene sequences for regional P. knowlesi isolates showed no obvious differentiation that could be attributed to their geographical origin. However, COX1 gene analysis showed that it was possible to differentiate between Singapore-acquired P. knowlesi infections and P. knowlesi infections from Peninsular Malaysia and Sarawak, Borneo, Malaysia.

    CONCLUSION: The ability to differentiate between locally acquired P. knowlesi infections and imported P. knowlesi infections has important utility for the monitoring of P. knowlesi malaria control programmes in Singapore.

    Matched MeSH terms: Plasmodium knowlesi/genetics*
  7. Assefa S, Lim C, Preston MD, Duffy CW, Nair MB, Adroub SA, et al.
    Proc Natl Acad Sci U S A, 2015 Oct 20;112(42):13027-32.
    PMID: 26438871 DOI: 10.1073/pnas.1509534112
    Malaria cases caused by the zoonotic parasite Plasmodium knowlesi are being increasingly reported throughout Southeast Asia and in travelers returning from the region. To test for evidence of signatures of selection or unusual population structure in this parasite, we surveyed genome sequence diversity in 48 clinical isolates recently sampled from Malaysian Borneo and in five lines maintained in laboratory rhesus macaques after isolation in the 1960s from Peninsular Malaysia and the Philippines. Overall genomewide nucleotide diversity (π = 6.03 × 10(-3)) was much higher than has been seen in worldwide samples of either of the major endemic malaria parasite species Plasmodium falciparum and Plasmodium vivax. A remarkable substructure is revealed within P. knowlesi, consisting of two major sympatric clusters of the clinical isolates and a third cluster comprising the laboratory isolates. There was deep differentiation between the two clusters of clinical isolates [mean genomewide fixation index (FST) = 0.21, with 9,293 SNPs having fixed differences of FST = 1.0]. This differentiation showed marked heterogeneity across the genome, with mean FST values of different chromosomes ranging from 0.08 to 0.34 and with further significant variation across regions within several chromosomes. Analysis of the largest cluster (cluster 1, 38 isolates) indicated long-term population growth, with negatively skewed allele frequency distributions (genomewide average Tajima's D = -1.35). Against this background there was evidence of balancing selection on particular genes, including the circumsporozoite protein (csp) gene, which had the top Tajima's D value (1.57), and scans of haplotype homozygosity implicate several genomic regions as being under recent positive selection.
    Matched MeSH terms: Plasmodium knowlesi/genetics*
  8. Fong MY, Lau YL, Chang PY, Anthony CN
    Parasit Vectors, 2014;7:161.
    PMID: 24693997 DOI: 10.1186/1756-3305-7-161
    The monkey malaria parasite Plasmodium knowlesi is now recognized as the fifth species of Plasmodium that can cause human malaria. Like the region II of the Duffy binding protein of P. vivax (PvDBPII), the region II of the P. knowlesi Duffy binding protein (PkDBPαII) plays an essential role in the parasite's invasion into the host's erythrocyte. Numerous polymorphism studies have been carried out on PvDBPII, but none has been reported on PkDBPαII. In this study, the genetic diversity, haplotyes and allele groups of PkDBPαII of P. knowlesi clinical isolates from Peninsular Malaysia were investigated.
    Matched MeSH terms: Plasmodium knowlesi/genetics
  9. Jiram AI, Vythilingam I, NoorAzian YM, Yusof YM, Azahari AH, Fong MY
    Malar J, 2012;11:213.
    PMID: 22727041
    The first natural infection of Plasmodium knowlesi in humans was recorded in 1965 in peninsular Malaysia. Extensive research was then conducted and it was postulated that it was a rare incident and that simian malaria will not be easily transmitted to humans. However, at the turn of the 21st century, knowlesi malaria was prevalent throughout Southeast Asia and is life threatening. Thus, a longitudinal study was initiated to determine the vectors, their seasonal variation and preference to humans and macaques.
    Matched MeSH terms: Plasmodium knowlesi/genetics
  10. Ta TT, Salas A, Ali-Tammam M, Martínez Mdel C, Lanza M, Arroyo E, et al.
    Malar J, 2010;9:219.
    PMID: 20663184 DOI: 10.1186/1475-2875-9-219
    Previously, Plasmodium knowlesi was not considered as a species of Plasmodium that could cause malaria in human beings, as it is parasite of long-tailed (Macaca fascicularis) and pig-tailed (Macaca nemestrina) macaques found in Southeast Asia. A case of infection by P. knowlesi is described in a Spanish traveller, who came back to Spain with daily fever after his last overseas travel, which was a six-month holiday in forested areas of Southeast Asia between 2008 and 2009. His P. knowlesi infection was detected by multiplex Real time quantitative PCR and confirmed by sequencing the amplified fragment. Using nested multiplex malaria PCR (reference method in Spain) and a rapid diagnostic test, the P. knowlesi infection was negative. This patient was discharged and asymptomatic when the positive result to P. knowlesi was reported. Prior to this case, there have been two more reports of European travellers with malaria caused by P. knowlesi, a Finnish man who travelled to Peninsular Malaysia during four weeks in March 2007, and a Swedish man who did a short visit to Malaysian Borneo in October 2006. Taken together with this report of P. knowlesi infection in a Spanish traveller returning from Southeast Asia, this is the third case of P. knowlesi infection in Europe, indicating that this simian parasite can infect visitors to endemic areas in Southeast Asia. This last European case is quite surprising, given that it is an untreated-symptomatic P. knowlesi in human, in contrast to what is currently known about P. knowlesi infection. Most previous reports of human P. knowlesi malaria infections were in adults, often with symptoms and relatively high parasite densities, up to the recent report in Ninh Thuan province, located in the southern part of central Vietnam, inhabited mainly by the Ra-glai ethnic minority, in which all P. knowlesi infections were asymptomatic, co-infected with P. malariae, with low parasite densities and two of the three identified cases were very young children under five years old.
    Matched MeSH terms: Plasmodium knowlesi/genetics
  11. Van den Eede P, Vythilingam I, Ngo DT, Nguyen VH, Le XH, D'Alessandro U, et al.
    Malar J, 2010;9:20.
    PMID: 20082717 DOI: 10.1186/1475-2875-9-20
    A recently published comment on a report of Plasmodium knowlesi infections in Vietnam states that this may not accurately represent the situation in the study area because the PCR primers used may cross-hybridize with Plasmodium vivax. Nevertheless, P. knowlesi infections have been confirmed by sequencing. In addition, a neighbour-joining tree based on the 18S S-Type SSUrRNA gene shows that the Vietnamese samples clearly cluster with the P. knowlesi isolates identified in Malaysia and are distinct from the corresponding P. vivax sequences. All samples came from asymptomatic individuals who did not consult for fever during the months preceding or following the survey, indicating that asymptomatic P. knowlesi infections occur in this population, although this does not exclude the occurrence of symptomatic cases. Large-scale studies to determine the extent and the epidemiology of P. knowlesi malaria in Vietnam are further needed.
    Matched MeSH terms: Plasmodium knowlesi/genetics
  12. Fong MY, Wong SS, Silva JR, Lau YL
    Acta Trop, 2015 Dec;152:145-150.
    PMID: 26384455 DOI: 10.1016/j.actatropica.2015.09.009
    The simian malaria parasite Plasmodium knowlesi is now recognized as a species that can cause human malaria. The first report of large scale human knowlesi malaria was in 2004 in Malaysia Borneo. Since then, hundreds of human knowlesi malaria cases have been reported in Southeast Asia. The present study investigates the genetic polymorphism of P. knowlesi DI domain of the apical membrane antigen-1 (AMA-1), a protein considered as a promising vaccine candidate for malaria. The DI domain of AMA-1 gene of P. knowlesi clinical isolates from Peninsular Malaysia was amplified by PCR, cloned into Escherichia coli, then sequenced and analysed. Ninety-seven DI domain sequences were obtained. Comparison at the nucleotide level against P. knowlesi strain H as reference sequence showed 21 synonymous and 25 nonsynonymous mutations. Nonetheless, nucleotide sequence analysis revealed low genetic diversity of the DI domain, and it was under purifying (negative) selection. At the amino acid level, 26 different haplotypes were identified and 2 were predominant haplotypes (H1, H2) with high frequencies. Phylogenetic analysis revealed that the 26 haplotypes could be clustered into 2 distinct groups (I and II). Members of the groups were basically derived from haplotypes H1 and H2, respectively.
    Matched MeSH terms: Plasmodium knowlesi/genetics*
  13. Benavente ED, Gomes AR, De Silva JR, Grigg M, Walker H, Barber BE, et al.
    Sci Rep, 2019 07 08;9(1):9873.
    PMID: 31285495 DOI: 10.1038/s41598-019-46398-z
    The zoonotic Plasmodium knowlesi parasite is the most common cause of human malaria in Malaysia. Genetic analysis has shown that the parasites are divided into three subpopulations according to their geographic origin (Peninsular or Borneo) and, in Borneo, their macaque host (Macaca fascicularis or M. nemestrina). Whilst evidence suggests that genetic exchange events have occurred between the two Borneo subpopulations, the picture is unclear in less studied Peninsular strains. One difficulty is that P. knowlesi infected individuals tend to present with low parasitaemia leading to samples with insufficient DNA for whole genome sequencing. Here, using a parasite selective whole genome amplification approach on unprocessed blood samples, we were able to analyse recent genomes sourced from both Peninsular Malaysia and Borneo. The analysis provides evidence that recombination events are present in the Peninsular Malaysia parasite subpopulation, which have acquired fragments of the M. nemestrina associated subpopulation genotype, including the DBPβ and NBPXa erythrocyte invasion genes. The NBPXb invasion gene has also been exchanged within the macaque host-associated subpopulations of Malaysian Borneo. Our work provides strong evidence that exchange events are far more ubiquitous than expected and should be taken into consideration when studying the highly complex P. knowlesi population structure.
    Matched MeSH terms: Plasmodium knowlesi/genetics*
  14. Atique Ahmed M, Kang HJ, Quan FS
    Korean J Parasitol, 2019 Aug;57(4):445-450.
    PMID: 31533414 DOI: 10.3347/kjp.2019.57.4.445
    Human infections due to the monkey malaria parasite Plasmodium knowlesi is increasingly being reported from most Southeast Asian countries specifically Malaysia. The parasite causes severe and fatal malaria thus there is a need for urgent measures for its control. In this study, the level of polymorphisms, haplotypes and natural selection of full-length pkmsp8 in 37 clinical samples from Malaysian Borneo along with 6 lab-adapted strains were investigated. Low levels of polymorphism were observed across the full-length gene, the double epidermal growth factor (EGF) domains were mostly conserved, and non-synonymous substitutions were absent. Evidence of strong negative selection pressure in the non-EGF regions were found indicating functional constrains acting at different domains. Phylogenetic haplotype network analysis identified shared haplotypes and indicated geographical clustering of samples originating from Peninsular Malaysia and Malaysian Borneo. This is the first study to genetically characterize the full-length msp8 gene from clinical isolates of P. knowlesi from Malaysia; however, further functional characterization would be useful for future rational vaccine design.
    Matched MeSH terms: Plasmodium knowlesi/genetics*
  15. Wilcox JS, Kerschner A, Hollocher H
    Infect Genet Evol, 2019 11;75:103994.
    PMID: 31421245 DOI: 10.1016/j.meegid.2019.103994
    Plasmodium knowlesi is an important causative agent of malaria in humans of Southeast Asia. Macaques are natural hosts for this parasite, but little is conclusively known about its patterns of transmission within and between these hosts. Here, we apply a comprehensive phylogenetic approach to test for patterns of cryptic population genetic structure between P. knowlesi isolated from humans and long-tailed macaques from the state of Sarawak in Malaysian Borneo. Our approach differs from previous investigations through our exhaustive use of archival 18S Small Subunit rRNA (18S) gene sequences from Plasmodium and Hepatocystis species, our inclusion of insertion and deletion information during phylogenetic inference, and our application of Bayesian phylogenetic inference to this problem. We report distinct clades of P. knowlesi that predominantly contained sequences from either human or macaque hosts for paralogous A-type and S-type 18S gene loci. We report significant partitioning of sequence distances between host species across both types of loci, and confirmed that sequences of the same locus type showed significantly biased assortment into different clades depending on their host species. Our results support the zoonotic potential of Plasmodium knowlesi, but also suggest that humans may be preferentially infected with certain strains of this parasite. Broadly, such patterns could arise through preferential zoonotic transmission of some parasite lineages or a disposition of parasites to transmit within, rather than between, human and macaque hosts. Available data are insufficient to address these hypotheses. Our results suggest that the epidemiology of P. knowlesi may be more complicated than previously assumed, and highlight the need for renewed and more vigorous explorations of transmission patterns in the fifth human malarial parasite.
    Matched MeSH terms: Plasmodium knowlesi/genetics
  16. Chua CY, Lee PC, Lau TY
    J Genet, 2017 Sep;96(4):653-663.
    PMID: 28947714
    The apical membrane antigen-1 (AMA-1) of Plasmodium spp. is a merozoite surface antigen that is essential for the recognition and invasion of erythrocytes. Polymorphisms occurring in this surface antigen will cause major obstacles in developing effective malaria vaccines based on AMA-1. The objective of this study was to characterize ama1 gene in Plasmodium knowlesi isolates from Sabah. DNA was extracted from blood samples collected from Keningau, Kota Kinabalu and Kudat. The Pkama1 gene was amplified using nested PCR and subjected to bidirectional sequencing. Analysis of DNA sequence revealed that most of the nucleotide polymorphisms were synonymous and concentrated in domain I of PkAMA-1. Forteen haplotypes were identified based on amino acid variations and haplotype K5 was the most common haplotype. dN/dS ratios implied that purifying selection was prevalent in Pkama1 gene. Fu and Li's D and F values further provided evidence of negative selection acting on domain II of Pkama1. Lownucleotide diversitywas also detected for the Pkama1 sequences,which is similar to reports on Pkama1 from Peninsular Malaysia and Sarawak. The presence of purifying selection and low nucleotide diversity indicated that domain II of Pkama1 can be used as a target for vaccine development.
    Matched MeSH terms: Plasmodium knowlesi/genetics*
  17. Ahmed MA, Quan FS
    Malar J, 2019 Apr 29;18(1):150.
    PMID: 31035999 DOI: 10.1186/s12936-019-2782-2
    BACKGROUND: The high proportion of human cases due to the simian malaria parasite Plasmodium knowlesi in Malaysia is a cause of concern, as they can be severe and even fatal. Merozoite surface protein 7 (MSP7) is a multigene family which forms a non-covalent complex with MSP-1 prior to receptor-ligand recognition in Plasmodium falciparum and thus an important antigen for vaccine development. However, no study has been done in any of the ortholog family members in P. knowlesi from clinical samples. This study investigates the level of polymorphism, haplotypes, and natural selection acting at the pkmsp-7D gene in clinical samples from Malaysia.

    METHODS: Thirty-six full-length pkmsp7D gene sequences (along with the reference H-strain: PKNH_1266000) obtained from clinical isolates of Malaysia, which were orthologous to pvmsp7H (PVX_082680) were downloaded from public databases. Population genetic, evolutionary and phylogenetic analyses were performed to determine the level of genetic diversity, polymorphism, recombination and natural selection.

    RESULTS: Analysis of 36 full-length pkmsp7D sequences identified 147 SNPs (91 non-synonymous and 56 synonymous substitutions). Nucleotide diversity across the full-length gene was higher than its ortholog in Plasmodium vivax (msp7H). Region-wise analysis of the gene indicated that the nucleotide diversity at the central region was very high (π = 0.14) compared to the 5' and 3' regions. Most hyper-variable SNPs were detected at the central domain. Multiple test for natural selection indicated the central region was under strong positive natural selection however, the 5' and 3' regions were under negative/purifying selection. Evidence of intragenic recombination were detected at the central region of the gene. Phylogenetic analysis using full-length msp7D genes indicated there was no geographical clustering of parasite population.

    CONCLUSIONS: High genetic diversity with hyper-variable SNPs and strong evidence of positive natural selection at the central region of MSP7D indicated exposure of the region to host immune pressure. Negative selection at the 5' and the 3' regions of MSP7D might be because of functional constraints at the unexposed regions during the merozoite invasion process of P. knowlesi. No evidence of geographical clustering among the clinical isolates from Malaysia indicated uniform selection pressure in all populations. These findings highlight the further evaluation of the regions and functional characterization of the protein as a potential blood stage vaccine candidate for P. knowlesi.

    Matched MeSH terms: Plasmodium knowlesi/genetics*
  18. Goh XT, Chua KH, Kee BP, Lim YAL
    Trop Med Int Health, 2020 02;25(2):172-185.
    PMID: 31733137 DOI: 10.1111/tmi.13348
    OBJECTIVE: Plasmodium knowlesi, the fifth human malaria parasite, has caused mortality in humans. We aimed to identify P. knowlesi novel binding peptides through a random linear dodecapeptide phage display targeting the 19-kDa fragment of Merozoite Surface Protein-1 protein.

    METHODS: rPkMSP-119 protein was heterologously expressed using Expresso® Solubility and Expression Screening System and competent E. cloni® 10G cells according to protocol. Three rounds of biopanning were performed on purified rPkMSP-119 to identify binding peptides towards rPkMSP-119 using Ph.D.™-12 random phage display library. Binding sites of the identified peptides to PkMSP-119 were in silico predicted using the CABS-dock web server.

    RESULTS: Four phage peptide variants that bound to PkMSP-119 were identified after three rounds of biopanning, namely Pkd1, Pkd2, Pkd3 and Pkd4. The sequences of both Pkd1 and Pkd2 consist of a large number of histidine residues. Pkd1 showed positive binding signal with 6.1× vs. BSA control. Docking results showed that Pkd1 and Pkd2 were ideal binding peptides for PkMSP-119 .

    CONCLUSION: We identified two novel binding peptides of PkMSP-119 , Pkd1 (HFPFHHHKLRAH) and Pkd2 (HPMHMLHKRQHG), through phage display. They provide a valuable starting point for the development of novel therapeutics.

    Matched MeSH terms: Plasmodium knowlesi/genetics*
  19. Lau YL, Cheong FW, Chin LC, Mahmud R, Chen Y, Fong MY
    Trop Biomed, 2014 Dec;31(4):749-59.
    PMID: 25776601 MyJurnal
    Malaria causes high global mortality and morbidity annually. Plasmodium knowlesi has been recognised as the fifth human Plasmodium sp. and its infection is widely distributed in Southeast Asia. Merozoite surface protein-119 (MSP-119) appears as a potential candidate for malaria blood stage vaccine as it could induce protective immunity. In this study, codon optimized P. knowlesi MSP-119 (pkMSP-119) was expressed and purified in yeast Pichia pastoris expression system. The purified recombinant protein was further evaluated using Western blot assay using knowlesi malaria, non-knowlesi human malaria, non-malarial parasitic infections and healthy serum samples (n = 50). The sensitivity of purified pkMSP-119 towards detection of knowlesi infection was as 28.6% (2/7). pkMSP-119 did not react with all non-malarial parasitic infections and healthy donor sera, yet reacted with some non-knowlesi human malaria sera, therefore lead to a specificity of 86.0% (37/43).
    Matched MeSH terms: Plasmodium knowlesi/genetics*
  20. Benavente ED, de Sessions PF, Moon RW, Grainger M, Holder AA, Blackman MJ, et al.
    Int J Parasitol, 2018 03;48(3-4):191-196.
    PMID: 29258833 DOI: 10.1016/j.ijpara.2017.09.008
    Plasmodium knowlesi, a common parasite of macaques, is recognised as a significant cause of human malaria in Malaysia. The P. knowlesi A1H1 line has been adapted to continuous culture in human erythrocytes, successfully providing an in vitro model to study the parasite. We have assembled a reference genome for the PkA1-H.1 line using PacBio long read combined with Illumina short read sequence data. Compared with the H-strain reference, the new reference has improved genome coverage and a novel description of methylation sites. The PkA1-H.1 reference will enhance the capabilities of the in vitro model to improve the understanding of P. knowlesi infection in humans.
    Matched MeSH terms: Plasmodium knowlesi/genetics*
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