Displaying publications 21 - 40 of 88 in total

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  1. De Silva JR, Lau YL, Fong MY
    Parasit Vectors, 2017 01 03;10(1):2.
    PMID: 28049516 DOI: 10.1186/s13071-016-1935-1
    BACKGROUND: The simian malaria parasite Plasmodium knowlesi has been reported to cause significant numbers of human infection in South East Asia. Its merozoite surface protein-3 (MSP3) is a protein that belongs to a multi-gene family of proteins first found in Plasmodium falciparum. Several studies have evaluated the potential of P. falciparum MSP3 as a potential vaccine candidate. However, to date no detailed studies have been carried out on P. knowlesi MSP3 gene (pkmsp3). The present study investigates the genetic diversity, and haplotypes groups of pkmsp3 in P. knowlesi clinical samples from Peninsular Malaysia.

    METHODS: Blood samples were collected from P. knowlesi malaria patients within a period of 4 years (2008-2012). The pkmsp3 gene of the isolates was amplified via PCR, and subsequently cloned and sequenced. The full length pkmsp3 sequence was divided into Domain A and Domain B. Natural selection, genetic diversity, and haplotypes of pkmsp3 were analysed using MEGA6 and DnaSP ver. 5.10.00 programmes.

    RESULTS: From 23 samples, 48 pkmsp3 sequences were successfully obtained. At the nucleotide level, 101 synonymous and 238 non-synonymous mutations were observed. Tests of neutrality were not significant for the full length, Domain A or Domain B sequences. However, the dN/dS ratio of Domain B indicates purifying selection for this domain. Analysis of the deduced amino acid sequences revealed 42 different haplotypes. Neighbour Joining phylogenetic tree and haplotype network analyses revealed that the haplotypes clustered into two distinct groups.

    CONCLUSIONS: A moderate level of genetic diversity was observed in the pkmsp3 and only the C-terminal region (Domain B) appeared to be under purifying selection. The separation of the pkmsp3 into two haplotype groups provides further evidence of the existence of two distinct P. knowlesi types or lineages. Future studies should investigate the diversity of pkmsp3 among P. knowlesi isolates in North Borneo, where large numbers of human knowlesi malaria infection still occur.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  2. Mahendran P, Liew JWK, Amir A, Ching XT, Lau YL
    Malar J, 2020 Jul 10;19(1):241.
    PMID: 32650774 DOI: 10.1186/s12936-020-03314-5
    BACKGROUND: Plasmodium knowlesi and Plasmodium vivax are the predominant Plasmodium species that cause malaria in Malaysia and play a role in asymptomatic malaria disease transmission in Malaysia. The diagnostic tools available to diagnose malaria, such as microscopy and rapid diagnostic test (RDT), are less sensitive at detecting lower parasite density. Droplet digital polymerase chain reaction (ddPCR), which has been shown to have higher sensitivity at diagnosing malaria, allows direct quantification without the need for a standard curve. The aim of this study is to develop and use a duplex ddPCR assay for the detection of P. knowlesi and P. vivax, and compare this method to nested PCR and qPCR.

    METHODS: The concordance rate, sensitivity and specificity of the duplex ddPCR assay were determined and compared to nested PCR and duplex qPCR.

    RESULTS: The duplex ddPCR assay had higher analytical sensitivity (P. vivax = 10 copies/µL and P. knowlesi = 0.01 copies/µL) compared to qPCR (P. vivax = 100 copies/µL and P. knowlesi = 10 copies/µL). Moreover, the ddPCR assay had acceptable clinical sensitivity (P. vivax = 80% and P. knowlesi = 90%) and clinical specificity (P. vivax = 87.84% and P. knowlesi = 81.08%) when compared to nested PCR. Both ddPCR and qPCR detected more double infections in the samples.

    CONCLUSIONS: Overall, the ddPCR assay demonstrated acceptable efficiency in detection of P. knowlesi and P. vivax, and was more sensitive than nested PCR in detecting mixed infections. However, the duplex ddPCR assay still needs optimization to improve the assay's clinical sensitivity and specificity.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  3. Moyes CL, Shearer FM, Huang Z, Wiebe A, Gibson HS, Nijman V, et al.
    Parasit Vectors, 2016 Apr 28;9:242.
    PMID: 27125995 DOI: 10.1186/s13071-016-1527-0
    BACKGROUND: Plasmodium knowlesi is a zoonotic pathogen, transmitted among macaques and to humans by anopheline mosquitoes. Information on P. knowlesi malaria is lacking in most regions so the first step to understand the geographical distribution of disease risk is to define the distributions of the reservoir and vector species.

    METHODS: We used macaque and mosquito species presence data, background data that captured sampling bias in the presence data, a boosted regression tree model and environmental datasets, including annual data for land classes, to predict the distributions of each vector and host species. We then compared the predicted distribution of each species with cover of each land class.

    RESULTS: Fine-scale distribution maps were generated for three macaque host species (Macaca fascicularis, M. nemestrina and M. leonina) and two mosquito vector complexes (the Dirus Complex and the Leucosphyrus Complex). The Leucosphyrus Complex was predicted to occur in areas with disturbed, but not intact, forest cover (> 60% tree cover) whereas the Dirus Complex was predicted to occur in areas with 10-100% tree cover as well as vegetation mosaics and cropland. Of the macaque species, M. nemestrina was mainly predicted to occur in forested areas whereas M. fascicularis was predicted to occur in vegetation mosaics, cropland, wetland and urban areas in addition to forested areas.

    CONCLUSIONS: The predicted M. fascicularis distribution encompassed a wide range of habitats where humans are found. This is of most significance in the northern part of its range where members of the Dirus Complex are the main P. knowlesi vectors because these mosquitoes were also predicted to occur in a wider range of habitats. Our results support the hypothesis that conversion of intact forest into disturbed forest (for example plantations or timber concessions), or the creation of vegetation mosaics, will increase the probability that members of the Leucosphyrus Complex occur at these locations, as well as bringing humans into these areas. An explicit analysis of disease risk itself using infection data is required to explore this further. The species distributions generated here can now be included in future analyses of P. knowlesi infection risk.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  4. Lai MY, Ooi CH, Lau YL
    Am J Trop Med Hyg, 2017 Nov;97(5):1597-1599.
    PMID: 28820700 DOI: 10.4269/ajtmh.17-0427
    In this study, we developed a recombinase polymerase amplification (RPA) assay for specific diagnosis of Plasmodium knowlesi. Genomic DNA was extracted from whole blood samples using a commercial kit. With incubation at 37°C, the samples were successfully amplified within 20 minutes. The end product of RPA was further examined by loading onto agarose gel and a specific band was observed with a size of 128 bp. The RPA assay exhibited high sensitivity with limits of detection down to one copy of the plasmid. From the specificity experiments, it was demonstrated that all P. knowlesi samples (N = 45) were positive while other Plasmodium spp. (N = 42) and negative samples (N = 6) were negative. Therefore, the RPA assay is a highly promising approach with the potential to be used in resource-limited settings. This assay can be further optimized for bedside and on field application.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  5. Divis PC, Shokoples SE, Singh B, Yanow SK
    Malar J, 2010 Nov 30;9:344.
    PMID: 21114872 DOI: 10.1186/1475-2875-9-344
    BACKGROUND: The misdiagnosis of Plasmodium knowlesi by microscopy has prompted a re-evaluation of the geographic distribution, prevalence and pathogenesis of this species using molecular diagnostic tools. In this report, a specific probe for P. knowlesi, that can be used in a previously described TaqMan real-time PCR assay for detection of Plasmodium spp., and Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae and Plasmodium ovale, was designed and validated against clinical samples.

    METHODS: A hydrolysis probe for a real-time PCR assay was designed to recognize a specific DNA sequence within the P. knowlesi small subunit ribosomal RNA gene. The sensitivity, linearity and specificity of the assay were determined using plasmids containing P. knowlesi DNA and genomic DNA of P. falciparum, P. knowlesi, P. malariae, P. ovale and P. vivax isolated from clinical samples. DNA samples of the simian malaria parasites Plasmodium cynomolgi and Plasmodium inui that can infect humans under experimental conditions were also examined together with human DNA samples.

    RESULTS: Analytical sensitivity of the P. knowlesi-specific assay was 10 copies/μL and quantitation was linear over a range of 10-106 copies. The sensitivity of the assay is equivalent to nested PCR and P. knowlesi DNA was detected from all 40 clinical P. knowlesi specimens, including one from a patient with a parasitaemia of three parasites/μL of blood. No cross-reactivity was observed with 67 Plasmodium DNA samples (31 P. falciparum, 23 P. vivax, six P. ovale, three P. malariae, one P. malariae/P. ovale, one P. falciparum/P. malariae, one P. inui and one P. cynomolgi) and four samples of human DNA.

    CONCLUSIONS: This test demonstrated excellent sensitivity and specificity, and adds P. knowlesi to the repertoire of Plasmodium targets for the clinical diagnosis of malaria by real-time PCR assays. Furthermore, quantitation of DNA copy number provides a useful advantage over other molecular assays to investigate the correlation between levels of infection and the spectrum of disease.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  6. De Silva JR, Lau YL, Fong MY
    PLoS One, 2014;9(9):e108951.
    PMID: 25268233 DOI: 10.1371/journal.pone.0108951
    The Duffy blood group is of major interest in clinical medicine as it plays an important role in Plasmodium knowlesi and Plasmodium vivax infection. In the present study, the distribution of Duffy blood group genotypes and allelic frequencies among P. knowlesi infected patients as well as healthy individuals in Peninsular Malaysia were determined. The blood group of 60 healthy blood donors and 51 P. knowlesi malaria patients were genotyped using allele specific polymerase chain reaction (ASP-PCR). The data was analyzed using Fisher's exact test in order to assess the significance of the variables. Our results show a high proportion of the FY*A/FY*A genotype (>85% for both groups) and a high frequency of the FY*A allele (>90% for both groups). The FY*A/FY*A genotype was the most predominant genotype in both infected and healthy blood samples. The genotype frequency did not differ significantly between the donor blood and the malaria patient groups. Also, there was no significant correlation between susceptibility to P. knowlesi infection with any Duffy blood genotype.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  7. William T, Jelip J, Menon J, Anderios F, Mohammad R, Awang Mohammad TA, et al.
    Malar J, 2014;13:390.
    PMID: 25272973 DOI: 10.1186/1475-2875-13-390
    While Malaysia has had great success in controlling Plasmodium falciparum and Plasmodium vivax, notifications of Plasmodium malariae and the microscopically near-identical Plasmodium knowlesi increased substantially over the past decade. However, whether this represents microscopic misdiagnosis or increased recognition of P. knowlesi has remained uncertain.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  8. Foster D, Cox-Singh J, Mohamad DS, Krishna S, Chin PP, Singh B
    Malar J, 2014;13:60.
    PMID: 24548805 DOI: 10.1186/1475-2875-13-60
    Plasmodium knowlesi, a malaria parasite of Southeast Asian macaques, infects humans and can cause fatal malaria. It is difficult to diagnose by microscopy because of morphological similarity to Plasmodium malariae. Nested PCR assay is the most accurate method to distinguish P. knowlesi from other Plasmodium species but is not cost effective in resource-poor settings. Rapid diagnostic tests (RDTs) are recommended for settings where malaria is prevalent. In this study, the effectiveness of three RDTs in detecting P. knowlesi from fresh and frozen patient blood samples was evaluated.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  9. Fatih FA, Staines HM, Siner A, Ahmed MA, Woon LC, Pasini EM, et al.
    Malar J, 2013;12:425.
    PMID: 24245918 DOI: 10.1186/1475-2875-12-425
    Evidence suggests that Plasmodium knowlesi malaria in Sarawak, Malaysian Borneo remains zoonotic, meaning anti-malarial drug resistance is unlikely to have developed in the absence of drug selection pressure. Therefore, adequate response to available anti-malarial treatments is assumed.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification
  10. Tanizaki R, Ujiie M, Kato Y, Iwagami M, Hashimoto A, Kutsuna S, et al.
    Malar J, 2013;12:128.
    PMID: 23587117 DOI: 10.1186/1475-2875-12-128
    This is the first case of Plasmodium knowlesi infection in a Japanese traveller returning from Malaysia. In September 2012, a previously healthy 35-year-old Japanese man presented to National Center for Global Health and Medicine in Tokyo with a two-day history of daily fever, mild headaches and mild arthralgia. Malaria parasites were found in the Giemsa-stained thin blood smear, which showed band forms similar to Plasmodium malariae. Although a nested PCR showed the amplification of the primer of Plasmodium vivax and Plasmodium knowlesi, he was finally diagnosed with P. knowlesi mono-infection by DNA sequencing. He was treated with mefloquine, and recovered without any complications. DNA sequencing of the PCR products is indispensable to confirm P. knowlesi infection, however there is limited access to DNA sequencing procedures in endemic areas. The extent of P. knowlesi transmission in Asia has not been clearly defined. There is limited availability of diagnostic tests and routine surveillance system for reporting an accurate diagnosis in the Asian endemic regions. Thus, reporting accurately diagnosed cases of P. knowlesi infection in travellers would be important for assessing the true nature of this emerging human infection.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  11. Lee WC, Chin PW, Lau YL, Chin LC, Fong MY, Yap CJ, et al.
    Malar J, 2013;12:88.
    PMID: 23496970 DOI: 10.1186/1475-2875-12-88
    Plasmodium knowlesi is a potentially life-threatening zoonotic malaria parasite due to its relatively short erythrocytic cycle. Microscopic identification of P. knowlesi is difficult, with "compacted parasite cytoplasm" being one of the important identifying keys. This report is about a case of hyperparasitaemic human P. knowlesi infection (27% parasitaemia) with atypical amoeboid morphology. A peninsular Malaysian was admitted to the hospital with malaria. He suffered anaemia and acute kidney function impairment. Microscopic examination, assisted by nested PCR and sequencing confirmed as P. knowlesi infection. With anti-malarial treatment and several medical interventions, patient survived and recovered. One-month medical follow-up was performed after recovery and no recrudescence was noted. This case report highlights the extreme hyperparasitaemic setting, the atypical morphology of P. knowlesi in the patient's erythrocytes, as well as the medical interventions involved in this successfully treated case.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  12. Kantele A, Jokiranta TS
    Clin Infect Dis, 2011 Jun;52(11):1356-62.
    PMID: 21596677 DOI: 10.1093/cid/cir180
    Human malaria has been known to be caused by 4 Plasmodium species, with Plasmodium falciparum causing the most-severe disease. Recently, numerous reports have described human malaria caused by a fifth Plasmodium species, Plasmodium knowlesi, which usually infects macaque monkeys. Hundreds of human cases have been reported from Malaysia, several cases have been reported in other Southeast Asian countries, and a few cases have been reported in travelers visiting these areas. Similarly to P. falciparum, P. knowlesi can cause severe and even fatal cases of disease that are more severe than those caused by the other Plasmodium species. Polymerase chain reaction is of value for diagnosis because P. knowlesi infection is easily misdiagnosed as less dangerous Plasmodium malariae infection with conventional microscopy. P. knowlesi infection should be suspected in patients who are infected with malaria in Southeast Asia. If human-mosquito-human transmission were to occur, the disease could spread to new areas where the mosquito vectors live, such as the popular tourist areas in western India.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  13. Lau YL, Fong MY, Mahmud R, Chang PY, Palaeya V, Cheong FW, et al.
    Malar J, 2011;10:197.
    PMID: 21774805 DOI: 10.1186/1475-2875-10-197
    The emergence of Plasmodium knowlesi in humans, which is in many cases misdiagnosed by microscopy as Plasmodium malariae due to the morphological similarity has contributed to the needs of detection and differentiation of malaria parasites. At present, nested PCR targeted on Plasmodium ssrRNA genes has been described as the most sensitive and specific method for Plasmodium detection. However, this method is costly and requires trained personnel for its implementation. Loop-mediated isothermal amplification (LAMP), a novel nucleic acid amplification method was developed for the clinical detection of P. knowlesi. The sensitivity and specificity of LAMP was evaluated in comparison to the results obtained via microscopic examination and nested PCR.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  14. Sabbatani S, Fiorino S, Manfredi R
    Braz J Infect Dis, 2010 May-Jun;14(3):299-309.
    PMID: 20835518
    After examining the most recent scientific evidences, which assessed the role of some malaria plasmodia that have monkeys as natural reservoirs, the authors focus their attention on Plasmodium knowlesi. The infective foci attributable to this last Plasmodium species have been identified during the last decade in Malaysia, in particular in the states of Sarawak and Sabah (Malaysian Borneo), and in the Pahang region (peninsular Malaysia). The significant relevance of molecular biology assays (polymerase chain reaction, or PCR, performed with specific primers for P. knowlesi), is underlined, since the traditional microscopic examination does not offer distinguishing features, especially when the differential diagnosis with Plasmodium malariae is of concern. Furthermore, Plasmodium knowlesi disease may be responsible of fatal cases, since its clinical presentation and course is more severe compared with those caused by P. malariae, paralleling a more elevated parasitemia. The most effective mosquito vector is represented by Anopheles latens; this mosquito is a parasite of both humans and monkeys. Among primates, the natural hosts are Macaca fascicularis, M. nemestina, M. inus, and Saimiri scirea. When remarking the possible severe evolution of P. knowlesi malaria, we underline the importance of an early recognition and a timely management, especially in patients who have their first onset in Western Hospitals, after journeys in Southeast Asian countries, and eventually participated in trekking excursions in the tropical forest. When malaria-like signs and symptoms are present, a timely diagnosis and treatment become crucial. In the light of its emerging epidemiological features, P. knowlesi may be added to the reknown human malaria parasites, whith includes P. vivax, P. ovale, P. malariae, and P. falciparum, as the fifth potential ethiologic agent of human malaria. Over the next few years, it will be mandatory to support an adequate surveillance and epidemiological network. In parallel with epidemiological and health care policy studies, also an accurate appraisal of the clinical features of P. knowlesi-affected patients will be strongly needed, since some preliminary experiences seem to show an increased disease severity, associated with increased parasitemia, in parallel with the progressive increase of inter-human infectious passages of this emerging Plasmodium.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  15. Cox-Singh J, Davis TM, Lee KS, Shamsul SS, Matusop A, Ratnam S, et al.
    Clin Infect Dis, 2008 Jan 15;46(2):165-71.
    PMID: 18171245 DOI: 10.1086/524888
    BACKGROUND: Until recently, Plasmodium knowlesi malaria in humans was misdiagnosed as Plasmodium malariae malaria. The objectives of the present study were to determine the geographic distribution of P. knowlesi malaria in the human population in Malaysia and to investigate 4 suspected fatal cases.

    METHODS: Sensitive and specific nested polymerase chain reaction was used to identify all Plasmodium species present in (1) blood samples obtained from 960 patients with malaria who were hospitalized in Sarawak, Malaysian Borneo, during 2001-2006; (2) 54 P. malariae archival blood films from 15 districts in Sabah, Malaysian Borneo (during 2003-2005), and 4 districts in Pahang, Peninsular Malaysia (during 2004-2005); and (3) 4 patients whose suspected cause of death was P. knowlesi malaria. For the 4 latter cases, available clinical and laboratory data were reviewed.

    RESULTS: P. knowlesi DNA was detected in 266 (27.7%) of 960 of the samples from Sarawak hospitals, 41 (83.7%) of 49 from Sabah, and all 5 from Pahang. Only P. knowlesi DNA was detected in archival blood films from the 4 patients who died. All were hyperparasitemic and developed marked hepatorenal dysfunction.

    CONCLUSIONS: Human infection with P. knowlesi, commonly misidentified as the more benign P. malariae, are widely distributed across Malaysian Borneo and extend to Peninsular Malaysia. Because P. knowlesi replicates every 24 h, rapid diagnosis and prompt effective treatment are essential. In the absence of a specific routine diagnostic test for P. knowlesi malaria, we recommend that patients who reside in or have traveled to Southeast Asia and who have received a "P. malariae" hyperparasitemia diagnosis by microscopy receive intensive management as appropriate for severe falciparum malaria.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  16. Barber BE, William T, Dhararaj P, Anderios F, Grigg MJ, Yeo TW, et al.
    Malar J, 2012;11:401.
    PMID: 23216947 DOI: 10.1186/1475-2875-11-401
    The simian parasite Plasmodium knowlesi is a common cause of human malaria in Malaysian Borneo, with a particularly high incidence in Kudat, Sabah. Little is known however about the epidemiology in this substantially deforested region.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  17. William T, Rahman HA, Jelip J, Ibrahim MY, Menon J, Grigg MJ, et al.
    PLoS Negl Trop Dis, 2013;7(1):e2026.
    PMID: 23359830 DOI: 10.1371/journal.pntd.0002026
    BACKGROUND: The simian parasite Plasmodium knowlesi is a common cause of human malaria in Malaysian Borneo and threatens the prospect of malaria elimination. However, little is known about the emergence of P. knowlesi, particularly in Sabah. We reviewed Sabah Department of Health records to investigate the trend of each malaria species over time.

    METHODS: Reporting of microscopy-diagnosed malaria cases in Sabah is mandatory. We reviewed all available Department of Health malaria notification records from 1992-2011. Notifications of P. malariae and P. knowlesi were considered as a single group due to microscopic near-identity.

    RESULTS: From 1992-2011 total malaria notifications decreased dramatically, with P. falciparum peaking at 33,153 in 1994 and decreasing 55-fold to 605 in 2011, and P. vivax peaking at 15,857 in 1995 and decreasing 25-fold to 628 in 2011. Notifications of P. malariae/P. knowlesi also demonstrated a peak in the mid-1990s (614 in 1994) before decreasing to ≈ 100/year in the late 1990s/early 2000s. However, P. malariae/P. knowlesi notifications increased >10-fold between 2004 (n = 59) and 2011 (n = 703). In 1992 P. falciparum, P. vivax and P. malariae/P. knowlesi monoinfections accounted for 70%, 24% and 1% respectively of malaria notifications, compared to 30%, 31% and 35% in 2011. The increase in P. malariae/P. knowlesi notifications occurred state-wide, appearing to have begun in the southwest and progressed north-easterly.

    CONCLUSIONS: A significant recent increase has occurred in P. knowlesi notifications following reduced transmission of the human Plasmodium species, and this trend threatens malaria elimination. Determination of transmission dynamics and risk factors for knowlesi malaria is required to guide measures to control this rising incidence.

    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  18. Faber BW, Abdul Kadir K, Rodriguez-Garcia R, Remarque EJ, Saul FA, Vulliez-Le Normand B, et al.
    PLoS One, 2015;10(4):e0124400.
    PMID: 25881166 DOI: 10.1371/journal.pone.0124400
    Infection with Plasmodium knowlesi, a zoonotic primate malaria, is a growing human health problem in Southeast Asia. P. knowlesi is being used in malaria vaccine studies, and a number of proteins are being considered as candidate malaria vaccine antigens, including the Apical Membrane Antigen 1 (AMA1). In order to determine genetic diversity of the ama1 gene and to identify epitopes of AMA1 under strongest immune selection, the ama1 gene of 52 P. knowlesi isolates derived from human infections was sequenced. Sequence analysis of isolates from two geographically isolated regions in Sarawak showed that polymorphism in the protein is low compared to that of AMA1 of the major human malaria parasites, P. falciparum and P. vivax. Although the number of haplotypes was 27, the frequency of mutations at the majority of the polymorphic positions was low, and only six positions had a variance frequency higher than 10%. Only two positions had more than one alternative amino acid. Interestingly, three of the high-frequency polymorphic sites correspond to invariant sites in PfAMA1 or PvAMA1. Statistically significant differences in the quantity of three of the six high frequency mutations were observed between the two regions. These analyses suggest that the pkama1 gene is not under balancing selection, as observed for pfama1 and pvama1, and that the PkAMA1 protein is not a primary target for protective humoral immune responses in their reservoir macaque hosts, unlike PfAMA1 and PvAMA1 in humans. The low level of polymorphism justifies the development of a single allele PkAMA1-based vaccine.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification*
  19. Pinheiro MM, Ahmed MA, Millar SB, Sanderson T, Otto TD, Lu WC, et al.
    PLoS One, 2015;10(4):e0121303.
    PMID: 25830531 DOI: 10.1371/journal.pone.0121303
    Plasmodium knowlesi is a newly described zoonosis that causes malaria in the human population that can be severe and fatal. The study of P. knowlesi parasites from human clinical isolates is relatively new and, in order to obtain maximum information from patient sample collections, we explored the possibility of generating P. knowlesi genome sequences from archived clinical isolates. Our patient sample collection consisted of frozen whole blood samples that contained excessive human DNA contamination and, in that form, were not suitable for parasite genome sequencing. We developed a method to reduce the amount of human DNA in the thawed blood samples in preparation for high throughput parasite genome sequencing using Illumina HiSeq and MiSeq sequencing platforms. Seven of fifteen samples processed had sufficiently pure P. knowlesi DNA for whole genome sequencing. The reads were mapped to the P. knowlesi H strain reference genome and an average mapping of 90% was obtained. Genes with low coverage were removed leaving 4623 genes for subsequent analyses. Previously we identified a DNA sequence dimorphism on a small fragment of the P. knowlesi normocyte binding protein xa gene on chromosome 14. We used the genome data to assemble full-length Pknbpxa sequences and discovered that the dimorphism extended along the gene. An in-house algorithm was developed to detect SNP sites co-associating with the dimorphism. More than half of the P. knowlesi genome was dimorphic, involving genes on all chromosomes and suggesting that two distinct types of P. knowlesi infect the human population in Sarawak, Malaysian Borneo. We use P. knowlesi clinical samples to demonstrate that Plasmodium DNA from archived patient samples can produce high quality genome data. We show that analyses, of even small numbers of difficult clinical malaria isolates, can generate comprehensive genomic information that will improve our understanding of malaria parasite diversity and pathobiology.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification
  20. Sonaimuthu P, Cheong FW, Chin LC, Mahmud R, Fong MY, Lau YL
    Exp Parasitol, 2015 Jun;153:118-22.
    PMID: 25812552 DOI: 10.1016/j.exppara.2015.03.010
    Malaria remains one of the world's most important infectious diseases and is responsible for enormous mortality and morbidity. Human infection with Plasmodium knowlesi is widely distributed in Southeast Asia. Merozoite surface protein-1₁₉ (MSP-1₁₉), which plays an important role in protective immunity against asexual blood stage malaria parasites, appears as a leading immunogenic antigen of Plasmodium sp. We evaluated the sensitivity and specificity of recombinant P. knowlesi MSP-1₁₉ (rMSP-1₁₉) for detection of malarial infection. rMSP-1₁₉ was expressed in Escherichia coli expression system and the purified rMSP-1₁₉ was evaluated with malaria, non-malaria and healthy human serum samples (n = 215) in immunoblots. The sensitivity of rMSP-1₁₉ for detection of P. knowlesi, Plasmodium falciparum, Plasmodium  vivax and Plasmodium  ovale infection was 95.5%, 75.0%, 85.7% and 100%, respectively. rMSP-1₁₉ did not react with all the non-malaria and healthy donor sera, which represents 100% specificity. The rMSP-1₁₉ could be used as a potential antigen in serodiagnosis of malarial infection in humans.
    Matched MeSH terms: Plasmodium knowlesi/isolation & purification
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