Displaying publications 1 - 20 of 220 in total

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  1. Braima KA, Sum JS, Ghazali AR, Muslimin M, Jeffery J, Lee WC, et al.
    PLoS One, 2013;8(10):e77924.
    PMID: 24194901 DOI: 10.1371/journal.pone.0077924
    BACKGROUND: The suburban transmission of malaria in Selangor, Malaysia's most developed and populous state still remains a concern for public health in this region. Despite much successful control efforts directed at its reduction, sporadic cases, mostly brought in by foreigners have continued to occur. In addition, cases of simian malaria caused by Plasmodium knowlesi, some with fatal outcome have caused grave concern to health workers. The aim of this study was to investigate the possibility of local malaria transmission in suburban regions of Selangor, which are adjacent to secondary rainforests.

    FINDINGS: A malaria survey spanning 7 years (2006 - 2012) was conducted in Selangor. A total of 1623 laboratory confirmed malaria cases were reported from Selangor's nine districts. While 72.6% of these cases (1178/1623) were attributed to imported malaria (cases originating from other countries), 25.5% (414/1623) were local cases and 1.9% (31/1623) were considered as relapse and unclassified cases combined. In this study, the most prevalent infection was P. vivax (1239 cases, prevalence 76.3%) followed by P. falciparum (211, 13.0%), P. knowlesi (75, 4.6%), P. malariae (71, 4.4%) and P. ovale (1, 0.06%). Mixed infections comprising of P. vivax and P. falciparum were confirmed (26, 1.6%). Entomological surveys targeting the residences of malaria patients' showed that the most commonly trapped Anopheles species was An. maculatus. No oocysts or sporozoites were found in the An. maculatus collected. Nevertheless, the possibility of An. maculatus being the malaria vector in the investigated locations was high due to its persistent occurrence in these areas.

    CONCLUSIONS: Malaria cases reported in this study were mostly imported cases. However the co-existence of local cases and potential Plasmodium spp. vectors should be cause for concern. The results of this survey reflect the need of maintaining closely monitored malaria control programs and continuous extensive malaria surveillance in Peninsula Malaysia.

  2. Mokhtar AS, Braima KA, Peng Chin H, Jeffery J, Mohd Zain SN, Rohela M, et al.
    J Med Entomol, 2016 Apr 25.
    PMID: 27113101 DOI: 10.1093/jme/tjw014
    We report a case of human intestinal myiasis in a 41-yr-old female patient presented at a clinic in Seri Kembangan, Selangor, Malaysia. Larvae passed out in the patient's feces were sent to the Department of Parasitology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia. DNA barcoding confirmed the second case of intestinal myiasis in Malaysia involving the larvae of Clogmia albipunctatus (Duckhouse) (Diptera: Psychodidae). We review reported cases of myiasis and discuss the present case of intestinal myiasis in an urban patient.
  3. Mokhtar AS, Sridhar GS, Mahmud R, Jeffery J, Lau YL, Wilson JJ, et al.
    J Med Entomol, 2016 Sep 01;53(5):1234-1237.
    PMID: 27208008 DOI: 10.1093/jme/tjw071
    We report an unusual cause of gastrointestinal infection occurring in a 1-year-old infant patient who was brought to a public hospital in Kuala Lumpur, Malaysia. Larvae passed out in the patient's feces were confirmed by DNA barcoding as belonging to the species, Lasioderma serricorne (F.), known as the cigarette beetle. We postulate that the larvae were acquired from contaminated food and were responsible for gastrointestinal symptoms in the patient. To our knowledge, this the first report of human canthariasis caused by larvae of L. serricorne.
  4. Muslimin M, Wilson JJ, Ghazali AR, Braima KA, Jeffery J, Wan-Nor F, et al.
    PMID: 25995738 DOI: 10.1186/s40409-015-0010-2
    The brown widow spider (Latrodectus geometricus Koch, 1841) has colonised many parts of the world from its continent of origin, Africa. By at least 1841, the species had successfully established populations in South America and has more recently expanded its range to the southern states of North America. This highly adaptable spider has been far more successful in finding its niche around the world than its famous cousins, the black widow, Latrodectus mactans, found in the south-eastern states of North America, and the red-back, Latrodectus hasselti, found mostly in Australia, New Zealand and Japan.
  5. Poh AH, Moghavvemi M, Shafiei MM, Leong CS, Lau YL, Mahamd Adikan FR, et al.
    PLoS One, 2017;12(6):e0178766.
    PMID: 28582398 DOI: 10.1371/journal.pone.0178766
    There are many products claiming to be an electronic solution towards repelling mosquitoes. Several reviews were published in debunking these claims. However, there is a lack of a systematic study on effects of electromagnetic (EM) or more specifically, radio frequency (RF) waves against mosquitoes due to the conclusions made in those years. Therefore, we attempt to establish a fundamental study on female Aedes Aegypti (Linnaeus) mosquitoes by quantifying the collective behavior of the mosquitoes against a continuous stream of low-powered RF signals via a broadband horn antenna using image processing methods. By examining the average lateral and vertical positions of the mosquitoes versus frequency and time, the data shows negligible consistency in the reactions of the mosquitoes toward the different frequencies ranging from 10 to 20,000.00 MHz, with a step of 10 MHz. This was done by examining 33 hours of spatiotemporal data, which was divided into three sessions. All three sessions showed totally different convolutions in the positions in arbitrary units based on the raster scan of the image processing output. Several frequencies apparently showed up to 0.2-70% shift in both lateral and vertical components along the spectrum, without repeatability for all three sessions. This study contributes to the following: A pilot study for establishing the collective effects of RF against mosquitoes, open-source use, and finally a low-cost and easily adaptable platform for the study of EM effects against any insects.
  6. Lau YL, Lai MY, Teoh BT, Abd-Jamil J, Johari J, Sam SS, et al.
    PLoS One, 2015;10(9):e0138694.
    PMID: 26384248 DOI: 10.1371/journal.pone.0138694
    Dengue is usually diagnosed by isolation of the virus, serology or molecular diagnostic methods. Several commercial kits for the diagnosis of dengue are existing, but concerns have arisen regarding to the affordability and performance characteristics of these kits. Hence, the loop-mediated isothermal amplification (LAMP) is potentially ideal to be used especially in resource limited environments. Serum was collected from healthy donors and patients diagnosed with dengue infection. RNA extracted from the serum samples were tested by reverse-transcription-LAMP assay developed based on 3'-NCR gene sequences for DENV 1-4. Results were interpreted by a turbidity meter in real time or visually at the end of the assay. Sensitivity and specificity of RT-LAMP results were calculated and compared to qRT-PCR and ELISA. RT-LAMP is highly sensitive with the detection limit of 10 RNA copies for all serotypes. Dengue virus RNA was detected in all positive samples using RT-LAMP and none of the negative samples within 30-45 minutes. With continuing efforts in the optimization of this assay, RT-LAMP may provide a simple and reliable test for detecting DENV in areas where dengue is prevalent.
  7. Fong MY, Lau YL, Chin LC, Al-Mekhlafi AM
    Trop Biomed, 2011 Aug;28(2):457-63.
    PMID: 22041769
    The cytochrome oxidase subunit I (COXI) gene sequences of three recent (2007-2008) clinical Plasmodium knowlesi isolates from Klang Valley, peninsular Malaysia, were determined and compared with those of older (1960's) peninsular Malaysia, recent isolates from Sarawak (on Borneo Island), and an isolate from Thailand. Multiple alignment of the sequences showed that the three clinical isolates were more similar to the older peninsular Malaysia isolates than to those from Sarawak and Thailand. Phylogenetic tree based on the COXI sequences revealed three distinct clusters of P. knowlesi. The first cluster consisted of isolates from peninsular Malaysia, the second consisted of Sarawak isolates and the third composed of the Thailand isolate. The findings of this study highlight the usefulness of mitochondrial COXI gene as a suitable marker for phylogeographic studies of P. knowlesi.
  8. Madkhali AM, Abdulhaq AA, Atroosh WM, Ghzwani AH, Zain KA, Ghailan KY, et al.
    Parasitol Res, 2021 Nov;120(11):3771-3781.
    PMID: 34561749 DOI: 10.1007/s00436-021-07323-4
    This study investigated the polymorphism in the P. falciparum chloroquine resistance transporter (pfcrt) gene 11 years after chloroquine (CQ) cessation in Jazan region, southwestern Saudi Arabia. Two hundred and thirty-five P. falciparum isolates were amplified to detect mutations in the pfcrt gene. The pfcrt 76 T molecular marker for CQ resistance was detected in 66.4% (156/235) of the isolates, while the K76 CQ-sensitive wild type was detected in 33.6%. The pfcrt 74I and pfcrt 75E point mutations were each found to be present in 56.2% of isolates, while only four isolates (1.7%) were found to carry the pfcrt 72S mutation. Moreover, four pfcrt haplotypes were identified as follows: the CVIET triple-allele (56.2%), SVMET double-allele (1.7%) and CVMNT single-allele (8.5%) mutant haplotypes and the CVMNK wild haplotype (33.6%). The analysis also revealed significant associations between the prevalence of mutant pfcrt alleles and haplotypes and the age group, governorate and nationality of the patients as well as the parasitaemia level (p 
  9. Atroosh WM, Lau YL, Snounou G, Azzani M, Al-Mekhlafi HM
    Malar J, 2022 Jan 04;21(1):2.
    PMID: 34983529 DOI: 10.1186/s12936-021-04014-4
    BACKGROUND: Genotyping of the three Plasmodium falciparum polymorphic genes, msp1, msp2 and glurp, has been adopted as a standard strategy to distinguish recrudescence from new infection in drug efficacy clinical trials. However, the suitability of a particular gene is compromised in areas where its allelic variants distribution is significantly skewed, a phenomenon that might occur in isolated parasite populations or in areas of very low transmission. Moreover, observation of amplification bias has diminished the value of glurp as a marker.

    METHODS: The suitability of the polymorphic P. falciparum histidine-rich protein 2 (pfhrp2) gene was assessed to serve as an alternative marker using a PCR-sequencing or a PCR-RFLP protocol for genotyping of samples in drug efficacy clinical trials. The value of pfhrp2 was validated by side-by-side analyses of 5 admission-recrudescence sample pairs from Yemeni malaria patients.

    RESULTS: The outcome of the single pfhrp2 gene discrimination analysis has been found consistent with msp1, msp2 and glurp pool genotyping analysis for the differentiation of recrudescence from new infection.

    CONCLUSION: The findings suggest that under the appropriate circumstances, pfhrp2 can serve as an additional molecular marker for monitoring anti-malarials efficacy. However, its use is restricted to endemic areas where only a minority of P. falciparum parasites lack the pfhrp2 gene.

  10. Ching XT, Lau YL, Fong MY, Nissapatorn V, Andiappan H
    Biomed Res Int, 2014;2014:690529.
    PMID: 24987700 DOI: 10.1155/2014/690529
    Toxoplasma gondii infects all warm-blooded animals, including humans, causing serious public health problems and great economic loss for the food industry. Commonly used serological tests require costly and hazardous preparation of whole Toxoplasma lysate antigens from tachyzoites. Here, we have evaluated an alternative method for antigen production, which involved a prokaryotic expression system. Specifically, we expressed T. gondii dense granular protein-5 (GRA5) in Escherichia coli and isolated it by affinity purification. The serodiagnostic potential of the purified recombinant GRA5 (rGRA5) was tested through Western blot analysis against 212 human patient serum samples. We found that rGRA5 protein was 100% specific for analysis of toxoplasmosis-negative human sera. Also, rGRA5 was able to detect acute and chronic T. gondii infections (sensitivities of 46.8% and 61.2%, resp.).
  11. 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.
  12. Andiappan H, Nissapatorn V, Sawangjaroen N, Chemoh W, Lau YL, Kumar T, et al.
    Parasit Vectors, 2014;7:239.
    PMID: 24886651 DOI: 10.1186/1756-3305-7-239
    Toxoplasmosis, being one of the TORCH's infections in pregnant women, is caused by Toxoplasma gondii, an obligate intracellular protozoan parasite. This parasitic infection in pregnancy congenitally causes severe outcomes to their fetus and newborn. This study aimed to determine the seroprevalence and stages of Toxoplasma infection in pregnant women and its associated risks exposures.
  13. Wong YP, Othman S, Lau YL, Radu S, Chee HY
    J Appl Microbiol, 2018 Mar;124(3):626-643.
    PMID: 29165905 DOI: 10.1111/jam.13647
    Loop-mediated isothermal amplification (LAMP) amplifies DNA with high specificity, efficiency and rapidity under isothermal conditions by using a DNA polymerase with high displacement strand activity and a set of specifically designed primers to amplify targeted DNA strands. Following its first discovery by Notomi et al. ( Nucleic Acids Res 28: E63), LAMP was further developed over the years which involved the combination of this technique with other molecular approaches, such as reverse transcription and multiplex amplification for the detection of infectious diseases caused by micro-organisms in humans, livestock and plants. In this review, available types of LAMP techniques will be discussed together with their applications in detection of various micro-organisms. Up to date, there are varieties of LAMP detection methods available including colorimetric and fluorescent detection, real-time monitoring using turbidity metre and detection using lateral flow device which will also be highlighted in this review. Apart from that, commercialization of LAMP technique had also been reported such as lyophilized form of LAMP reagents kit and LAMP primer sets for detection of pathogenic micro-organisms. On top of that, advantages and limitations of this molecular detection method are also described together with its future potential as a diagnostic method for infectious disease.
  14. Mu AK, Bee PC, Lau YL, Chen Y
    Int J Mol Sci, 2014;15(11):19952-61.
    PMID: 25372941 DOI: 10.3390/ijms151119952
    Malaria is caused by parasitic protozoans of the genus Plasmodium and is one of the most prevalent infectious diseases in tropical and subtropical regions. For this reason, effective and practical diagnostic methods are urgently needed to control the spread of malaria. The aim of the current study was to identify a panel of new malarial markers, which could be used to diagnose patients infected with various Plasmodium species, including P. knowlesi, P. vivax and P. falciparum. Sera from malaria-infected patients were pooled and compared to control sera obtained from healthy individuals using the isobaric tags for relative and absolute quantitation (iTRAQ) technique. Mass spectrometry was used to identify serum proteins and quantify their relative abundance. We found that the levels of several proteins were increased in pooled serum from infected patients, including cell adhesion molecule-4 and C-reactive protein. In contrast, the serum concentration of haptoglobin was reduced in malaria-infected individuals, which we verified by western blot assay. Therefore, these proteins might represent infectious markers of malaria, which could be used to develop novel diagnostic tools for detecting P. knowlesi, P. vivax and P. falciparum. However, these potential malarial markers will need to be validated in a larger population of infected individuals.
  15. 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.
  16. Syahmi AR, Vijayarathna S, Sasidharan S, Latha LY, Kwan YP, Lau YL, et al.
    Molecules, 2010 Nov;15(11):8111-21.
    PMID: 21072022 DOI: 10.3390/molecules15118111
    Elaeis guineensis (Arecaceae) is widely used in West African traditional medicine for treating various ailments. An evaluation on the toxicity of extracts of this plant is crucial to support the therapeutic claims. The acute oral toxicity and brine shrimp lethality of a methanolic extract of this plant was tested. Oral administration of crude extract at the highest dose of 5,000 mg/kg resulted in no mortalities or evidence of adverse effects, implying that E. guineensis is nontoxic. Normal behavioral pattern, clinical signs and histology of vital organs confirm this evidence. The E. guineensis extracts screened for toxicity against brine shrimp had 50% lethal concentration (LC₅₀) values of more than 1.0 mg/mL (9.00 and 3.87 mg/mL, at 6 and 24 h, respectively), confirming that the extract was not toxic. Maximum mortalities occurred at 100 mg/mL concentration while the least mortalities happened to be at 0.195 mg/mL concentration. The results of both tests confirm that E. guineensis is nontoxic and hence safe for commercial utilization.
  17. Lau YL, Meganathan P, Sonaimuthu P, Thiruvengadam G, Nissapatorn V, Chen Y
    J Clin Microbiol, 2010 Oct;48(10):3698-702.
    PMID: 20660217 DOI: 10.1128/JCM.00462-10
    Loop-mediated isothermal amplification (LAMP), a rapid nucleic acid amplification method, was developed for the clinical diagnosis of toxoplasmosis. Three LAMP assays based on the SAG1, SAG2, and B1 genes of Toxoplasma gondii were developed. The sensitivities and specificities of the LAMP assays were evaluated by comparison with the results of conventional nested PCR. The LAMP assays were highly sensitive and had a detection limit of 0.1 tachyzoite, and no cross-reactivity with the DNA of other parasites was observed. Blood was collected from 105 individuals to test the LAMP assays: 40 patients with active toxoplasmosis, 40 negative controls, and 25 patients with other parasitic infections. The SAG2-based LAMP (SAG2-LAMP) had a greater sensitivity (87.5%) than the SAG1-LAMP (80%), B1-LAMP (80%), and nested PCR (62.5%). All the LAMP assays and nested PCR were 100% specific. This is the first report of a study which applied the LAMP method to diagnose toxoplasmosis from human blood samples. Due to its simplicity, sensitivity, and specificity, LAMP is suggested as an appropriate method for routine diagnosis of active toxoplasmosis in humans.
  18. Fong MY, Lau YL, Jelip J, Ooi CH, Cheong FW
    J Genet, 2019 Sep;98.
    PMID: 31544794
    Plasmodium knowlesi contributes to the majority of human malaria incidences in Malaysia. Its uncontrollable passage among the natural monkey hosts can potentially lead to zoonotic outbreaks. The merozoite of this parasite invades host erythrocytes through interaction between its erythrocyte-binding proteins (EBPs) and their respective receptor on the erythrocytes. The regionII of P. knowlesi EBP, P. knowlesi beta (PkβII) protein is found to be mediating merozoite invasion into monkey erythrocytes by interacting with sialic acid receptors. Hence, the objective of this study was to investigate the genetic diversity, natural selection and haplotype grouping of PkβII of P. knowlesi isolates in Malaysia. Polymerase chain reaction amplifications of PkβII were performed on archived blood samples from Malaysia and 64 PkβII sequences were obtained. Sequence analysis revealed length polymorphism, and its amino acids at critical residues indicate the ability of PkβII to mediate P. knowlesi invasion into monkey erythrocytes. Low genetic diversity (π = 0.007) was observed in the PkβII of Malaysia Borneo compared to Peninsular Malaysia (π = 0.015). The PkβII was found to be under strong purifying selection to retain infectivity in monkeys and it plays a limited role in the zoonotic potential of P. knowlesi. Its haplotypes could be clustered into Peninsular Malaysia and Malaysia Borneo groups, indicating the existence of two distinct P. knowlesi parasites in Malaysia as reported in an earlier study.
  19. Liew CC, Lau YL, Fong MY, Cheong FW
    Am J Trop Med Hyg, 2020 05;102(5):1068-1071.
    PMID: 32189613 DOI: 10.4269/ajtmh.19-0836
    Invasion of human erythrocytes by merozoites of Plasmodium knowlesi involves interaction between the P. knowlesi Duffy binding protein alpha region II (PkDBPαII) and Duffy antigen receptor for chemokines (DARCs) on the erythrocytes. Information is scarce on the binding level of PkDBPαII to different Duffy antigens, Fya and Fyb. This study aims to measure the binding level of two genetically distinct PkDBPαII haplotypes to Fy(a+b-) and Fy(a+b+) human erythrocytes using erythrocyte-binding assay. The binding level of PkDBPαII of Peninsular Malaysian and Malaysian Borneon haplotypes to erythrocytes was determined by counting the number of rosettes formed in the assay. Overall, the Peninsular Malaysian haplotype displayed higher binding activity than the Malaysian Borneon haplotype. Both haplotypes exhibit the same preference to Fy(a+b+) compared with Fy(a+b-), hence justifying the vital role of Fyb in the binding to PkDBPαII. Further studies are needed to investigate the P. knowlesi susceptibility on individuals with different Duffy blood groups.
  20. Lau YL, Fong MY, Idris MM, Ching XT
    PMID: 23082548
    Detection of Toxoplasma gondii infection is essential in pregnant women and immunosuppressed patients. Numerous studies have shown that the recombinant production of several Toxoplasma antigens, including dense granule antigens (GRAs) has high potential as diagnostic reagents. In the present study, we produced GRA2 using Pichia pastoris system. RNA of T. gondii RH strain tachyzoite was used as a template to produce cDNA clones of full-length GRA2 via reverse transcriptase PCR. Amplicons were inserted into pPICZalpha A and the recombinant plasmid transformed into P. pastoris, X-33 strain. The expressed recombinant protein was identified by SDS-PAGE and Western blotting. A recombinant protein of -28 kDa was produced, which could be detected by toxoplasmosis positive human sera indicating that the recombinant protein retained its antigenicity. The present study indicates that P. pastoris-expressed GRA2 should be useful for detection of Toxoplasma infection.
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