Displaying publications 161 - 180 of 220 in total

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  1. Phang WK, Hamid MHBA, Jelip J, Mudin RNB, Chuang TW, Lau YL, et al.
    Front Microbiol, 2023;14:1126418.
    PMID: 36876062 DOI: 10.3389/fmicb.2023.1126418
    The emergence of potentially life-threatening zoonotic malaria caused by Plasmodium knowlesi nearly two decades ago has continued to challenge Malaysia healthcare. With a total of 376 P. knowlesi infections notified in 2008, the number increased to 2,609 cases in 2020 nationwide. Numerous studies have been conducted in Malaysian Borneo to determine the association between environmental factors and knowlesi malaria transmission. However, there is still a lack of understanding of the environmental influence on knowlesi malaria transmission in Peninsular Malaysia. Therefore, our study aimed to investigate the ecological distribution of human P. knowlesi malaria in relation to environmental factors in Peninsular Malaysia. A total of 2,873 records of human P. knowlesi infections in Peninsular Malaysia from 1st January 2011 to 31st December 2019 were collated from the Ministry of Health Malaysia and geolocated. Three machine learning-based models, maximum entropy (MaxEnt), extreme gradient boosting (XGBoost), and ensemble modeling approach, were applied to predict the spatial variation of P. knowlesi disease risk. Multiple environmental parameters including climate factors, landscape characteristics, and anthropogenic factors were included as predictors in both predictive models. Subsequently, an ensemble model was developed based on the output of both MaxEnt and XGBoost. Comparison between models indicated that the XGBoost has higher performance as compared to MaxEnt and ensemble model, with AUCROC values of 0.933 ± 0.002 and 0.854 ± 0.007 for train and test datasets, respectively. Key environmental covariates affecting human P. knowlesi occurrence were distance to the coastline, elevation, tree cover, annual precipitation, tree loss, and distance to the forest. Our models indicated that the disease risk areas were mainly distributed in low elevation (75-345 m above mean sea level) areas along the Titiwangsa mountain range and inland central-northern region of Peninsular Malaysia. The high-resolution risk map of human knowlesi malaria constructed in this study can be further utilized for multi-pronged interventions targeting community at-risk, macaque populations, and mosquito vectors.
  2. Phang WK, Hamid MHBA, Jelip J, Mudin RNB, Chuang TW, Lau YL, et al.
    Front Microbiol, 2023;14:1178864.
    PMID: 37007492 DOI: 10.3389/fmicb.2023.1178864
    [This corrects the article DOI: 10.3389/fmicb.2023.1126418.].
  3. Lee WC, Cheong FW, Amir A, Lai MY, Tan JH, Phang WK, et al.
    Malar J, 2023 Oct 19;22(1):316.
    PMID: 37858164 DOI: 10.1186/s12936-023-04732-x
  4. Latif ENM, Noordin NR, Shahari S, Amir A, Lau YL, Cheong FW, et al.
    Parasitol Res, 2024 Jan 19;123(1):105.
    PMID: 38240877 DOI: 10.1007/s00436-024-08125-0
    Plasmodium cynomolgi is a simian malaria parasite that has been increasingly infecting humans. It is naturally present in the long-tailed and pig-tailed macaques in Southeast Asia. The P. cynomolgi Duffy binding protein 1 region II [PcDBP1(II)] plays an essential role in the invasion of the parasite into host erythrocytes. This study investigated the genetic polymorphism, natural selection and haplotype clustering of PcDBP1(II) from wild macaque isolates in Peninsular Malaysia. The genomic DNA of 50 P. cynomolgi isolates was extracted from the macaque blood samples. Their PcDBP1(II) gene was amplified using a semi-nested PCR, cloned into a plasmid vector and subsequently sequenced. The polymorphism, natural selection and haplotypes of PcDBP1(II) were analysed using MEGA X and DnaSP ver.6.12.03 programmes. The analyses revealed high genetic polymorphism of PcDBP1(II) (π = 0.026 ± 0.004; Hd = 0.996 ± 0.001), and it was under purifying (negative) selection. A total of 106 haplotypes of PcDBP1(II) were identified. Phylogenetic and haplotype analyses revealed two groups of PcDBP1(II). Amino acid length polymorphism was observed between the groups, which may lead to possible phenotypic difference between them.
  5. Shahari S, Bin Abdullah ML, Binti Isman Rohimly AA, Binti Ashrat N, Amir A, Atroosh WMM, et al.
    Sci Rep, 2024 Mar 12;14(1):6023.
    PMID: 38472278 DOI: 10.1038/s41598-024-54981-2
    The parasite Plasmodium knowlesi has been the sole cause of malaria in Malaysia from 2018 to 2022. The persistence of this zoonotic species has hampered Malaysia's progress towards achieving the malaria-free status awarded by the World Health Organisation (WHO). Due to the zoonotic nature of P. knowlesi infections, it is important to study the prevalence of the parasite in the macaque host, the long-tailed macaque (Macaca fascicularis). Apart from P. knowlesi, the long-tailed macaque is also able to harbour Plasmodium cynomolgi, Plasmodium inui, Plasmodium caotneyi and Plasmodium fieldi. Here we report the prevalence of the 5 simian malaria parasites in the wild long-tailed macaque population in 12 out of the 13 states in Peninsular Malaysia using a nested PCR approach targeting the 18s ribosomal RNA (18s rRNA) gene. It was found that all five Plasmodium species were widely distributed throughout Peninsular Malaysia except for states with major cities such as Kuala Lumpur and Putrajaya. Of note, Pahang reported a malaria prevalence of 100% in the long-tailed macaque population, identifying it as a potential hotspot for zoonotic transmission. Overall, this study shows the distribution of the 5 simian malaria parasite species throughout Peninsular Malaysia, the data of which could be used to guide future malaria control interventions to target zoonotic malaria.
  6. Chin EZ, Chang WJ, Tan HY, Liew SY, Lau YL, Ng YL, et al.
    Bioorg Med Chem Lett, 2024 May 01;103:129701.
    PMID: 38484804 DOI: 10.1016/j.bmcl.2024.129701
    Malaria, a devastating disease, has claimed numerous lives and caused considerable suffering, with young children and pregnant women being the most severely affected group. However, the emergence of multidrug-resistant strains of Plasmodium and the adverse side effects associated with existing antimalarial drugs underscore the urgent need for the development of novel, well-tolerated, and more efficient drugs to combat this global health threat. To address these challenges, six new hydantoins derivatives were synthesized and evaluated for their in vitro antiplasmodial activity. Notably, compound 2c exhibited excellent inhibitory activity against the tested Pf3D7 strain, with an IC50 value of 3.97 ± 0.01 nM, three-fold better than chloroquine. Following closely, compound 3b demonstrated an IC50 value of 27.52 ± 3.37 µM against the Pf3D7 strain in vitro. Additionally, all the hydantoins derivatives tested showed inactive against human MCR-5 cells, with an IC50 value exceeding 100 μM. In summary, the hydantoin derivative 2c emerges as a promising candidate for further exploration as an antiplasmodial compound.
  7. Muh F, Ahmed MA, Han JH, Nyunt MH, Lee SK, Lau YL, et al.
    Sci Rep, 2018 04 10;8(1):5781.
    PMID: 29636493 DOI: 10.1038/s41598-018-23728-1
    The Plasmodium falciparum apical asparagine (Asn)-rich protein (AARP) is one of malarial proteins, and it has been studied as a candidate of malaria subunit vaccine. Basic characterization of PvAARP has been performed with a focus on its immunogenicity and localization. In this study, we further analyzed the immunogenicity of PvAARP, focusing on the longevity of the antibody response, cross-species immunity and invasion inhibitory activity by using the primate malaria parasite Plasmodium knowlesi. We found that vivax malaria patient sera retained anti-PvAARP antibodies for at least one year without re-infection. Recombinant PvAARP protein was strongly recognized by knowlesi malaria patients. Antibody raised against the P. vivax and P. knowlesi AARP N-termini reacted with the apical side of the P. knowlesi merozoites and inhibited erythrocyte invasion by P. knowlesi in a concentration-dependent manner, thereby suggesting a cross-species nature of anti-PvAARP antibody against PkAARP. These results can be explained by B cell epitopes predicted in conserved surface-exposed regions of the AARP N-terminus in both species. The long-lived anti-PvAARP antibody response, cross-reactivity, and invasion inhibitory activity of anti-PvAARP support a critical role of AARP during the erythrocyte invasion and suggest that PvAARP induces long-lived cross-species protective immunity against P. vivax and P. knowlesi.
  8. Syahmi AR, Vijayarathna S, Sasidharan S, Latha LY, Kwan YP, Lau YL, et al.
    Molecules, 2010 Nov 10;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.
  9. Andiappan H, Nissapatorn V, Sawangjaroen N, Nyunt MH, Lau YL, Khaing SL, et al.
    Parasit Vectors, 2014;7:564.
    PMID: 25498432 DOI: 10.1186/s13071-014-0564-9
    Toxoplasma gondii, an obligate intracellular protozoan parasite, causes a disease called toxoplasmosis which can sometimes be acquired congenitally by a newborn from an infected mother. This study aimed to determine the seroprevalence of Toxoplasma infection and its associated risks among 219 and 215 pregnant women from Malaysia and Myanmar, respectively.
  10. Andiappan H, Nissapatorn V, Sawangjaroen N, Khaing SL, Salibay CC, Cheung MM, et al.
    Front Microbiol, 2014;5:291.
    PMID: 24966855 DOI: 10.3389/fmicb.2014.00291
    Toxoplasma gondii, is one of the infectious agents of congenital TORCH infections, causes severe clinical outcomes in fetus and newborns. Nevertheless this life-threatening parasitic disease is preventable by simple preventive measures related to lifestyle during pregnancy. We aim to study on the knowledge about toxoplasmosis and practices that prevents this infection among the pregnant women. Total of 2598 pregnant women from Malaysia, Philippines, and Thailand were randomly surveyed to determine the knowledge and their practices on Toxoplasma infection. The questionnaire covered respondents' general information and knowledge on plausible risks factors, symptoms, timing of infection, prevention knowledge, and preventive behavior regarding Toxoplasma infection. Majority of these pregnant women were in their age group of 20-29 years (50.9%), completed secondary level of education (51.7%), in their second trimester of pregnancies (38.1%), non-parous (36.6%), and had no history of abortion (90.4%). Based on this survey, only 11% of these pregnant women had read, heard, or seen information regarding toxoplasmosis and 3.5% of them were aware of being tested for the infection. A small percentage of these pregnant women knew that T. gondii were shed in the feces of infected cats (19.4%) and sometimes found in the raw or undercooked meat (11.0%). There was 16.1% of responding women knew that toxoplasmosis is caused by an infection. Demographic profiles such as age group, level of education, pregnancy term, and number of children of the pregnant women showed significant association with their responses toward prevention knowledge and preventive behavior related questions (P < 0.05). Thus, it is suggested that health education on toxoplasmosis and primary behavioral practices should be consistently offered to reproductive age women in general and pregnant women in particular. This information could help to reduce vertical transmission of Toxoplasma infection during pregnancy.
  11. Onichandran S, Kumar T, Salibay CC, Dungca JZ, Tabo HA, Tabo N, et al.
    Parasit Vectors, 2014;7:244.
    PMID: 24885105 DOI: 10.1186/1756-3305-7-244
    Despite the amount of awareness created, waterborne disease still poses threat, especially in developing countries. Due to the scarcity of reported data on waterborne parasites, the consumption of unsafe water prolongs. Thus, the occurrences of waterborne parasites from various samples were investigated from one of the Southeast Asian country, the Philippines.
  12. 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.
  13. 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.
  14. Atroosh WM, Al-Mekhlafi HM, Al-Jasari A, Sady H, Al-Delaimy AK, Nasr NA, et al.
    Parasit Vectors, 2015;8:388.
    PMID: 26198252 DOI: 10.1186/s13071-015-1008-x
    The genetic variation in the Plasmodium falciparum histidine-rich protein 2 (pfhrp2) gene that may compromise the use of pfhrp2-based rapid diagnostic tests (RDTs) for the diagnosis of malaria was assessed in P. falciparum isolates from Yemen.
  15. Amir A, Shahari S, Liew JWK, de Silva JR, Khan MB, Lai MY, et al.
    Acta Trop, 2020 Nov;211:105596.
    PMID: 32589995 DOI: 10.1016/j.actatropica.2020.105596
    Zoonotic cases of Plasmodium knowlesi account for most malaria cases in Malaysia, and humans infected with P. cynomolgi, another parasite of macaques have recently been reported in Sarawak. To date the epidemiology of malaria in its natural Macaca reservoir hosts remains little investigated. In this study we surveyed the prevalence of simian malaria in wild macaques of three states in Peninsular Malaysia, namely Pahang, Perak and Johor using blood samples from 103 wild macaques (collected by the Department of Wildlife and National Parks Peninsular Malaysia) subjected to microscopic examination and nested PCR targeting the Plasmodium small subunit ribosomal RNA gene. As expected, PCR analysis yielded significantly higher prevalence (64/103) as compared to microscopic examination (27/103). No relationship between the age and/or sex of the macaques with the parasitaemia and the Plasmodium species infecting the macaques could be identified. Wild macaques in Pahang had the highest prevalence of Plasmodium parasites (89.7%), followed by those of Perak (69.2%) and Johor (28.9%). Plasmodium inui and P. cynomolgi were the two most prevalent species infecting the macaques from all three states. Half of the macaques (33/64) harboured two or more Plasmodium species. These data provide a baseline survey, which should be extended by further longitudinal investigations that should be associated with studies on the bionomics of the anopheline vectors. This information will allow an accurate evaluation of the risk of zoonotic transmission to humans, and to elaborate effective strategies to control simian malaria.
  16. Yang W, Lee PP, Thong MK, Ramanujam TM, Shanmugam A, Koh MT, et al.
    Clin Genet, 2015 Dec;88(6):542-9.
    PMID: 25534311 DOI: 10.1111/cge.12553
    Familial multiple intestinal atresias is an autosomal recessive disease with or without combined immunodeficiency. In the last year, several reports have described mutations in the gene TTC7A as causal to the disease in different populations. However, exact correlation between different genotypes and various phenotypes are not clear. In this study, we report identification of novel compound heterozygous mutations in TTC7A gene in a Malay girl with familial multiple intestinal atresias and severe combined immunodeficiency (MIA-SCID) by whole exome sequencing. We found two mutations in TTC7A: one that destroyed a putative splicing acceptor at the junction of intron 17/exon 18 and one that introduced a stop codon that would truncate the last two amino acids of the encoded protein. Reviewing the recent reports on TTC7A mutations reveals correlation between the position and nature of the mutations with patient survival and clinical manifestations. Examination of public databases also suggests carrier status for healthy individuals, making a case for population screening on this gene, especially in populations with suspected frequent founder mutations.
  17. Lau YL, Ismail IB, Izati Binti Mustapa N, Lai MY, Tuan Soh TS, Hassan AH, et al.
    Am J Trop Med Hyg, 2020 Dec;103(6):2350-2352.
    PMID: 33098286 DOI: 10.4269/ajtmh.20-1079
    A simple and rapid reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay was developed for the detection of SARS-CoV-2. The RT-LAMP assay was highly specific for SARS-CoV-2 and was able to detect one copy of transcribed SARS-CoV-2 RNA within 24 minutes. Assay validation performed using 50 positive and 32 negative clinical samples showed 100% sensitivity and specificity. The RT-LAMP would be valuable for clinical diagnosis and epidemiological surveillance of SARS-CoV-2 infection in resource-limited areas as it does not require the use of sophisticated and costly equipment.
  18. Lee WC, Malleret B, Lau YL, Mauduit M, Fong MY, Cho JS, et al.
    Blood, 2014 May 01;123(18):e100-9.
    PMID: 24652986 DOI: 10.1182/blood-2013-12-541698
    Rosetting phenomenon has been linked to malaria pathogenesis. Although rosetting occurs in all causes of human malaria, most data on this subject has been derived from Plasmodium falciparum. Here, we investigate the function and factors affecting rosette formation in Plasmodium vivax. To achieve this, we used a range of novel ex vivo protocols to study fresh and cryopreserved P vivax (n = 135) and P falciparum (n = 77) isolates from Thailand. Rosetting is more common in vivax than falciparum malaria, both in terms of incidence in patient samples and percentage of infected erythrocytes forming rosettes. Rosetting to P vivax asexual and sexual stages was evident 20 hours postreticulocyte invasion, reaching a plateau after 30 hours. Host ABO blood group, reticulocyte count, and parasitemia were not correlated with P vivax rosetting. Importantly, mature erythrocytes (normocytes), rather than reticulocytes, preferentially form rosetting complexes, indicating that this process is unlikely to directly facilitate merozoite invasion. Although antibodies against host erythrocyte receptors CD235a and CD35 had no effect, Ag-binding fragment against the BRIC 4 region of CD236R significantly inhibited rosette formation. Rosetting assays using CD236R knockdown normocytes derived from hematopoietic stem cells further supports the role of glycophorin C as a receptor in P vivax rosette formation.
  19. Al-Areeqi MA, Sady H, Al-Mekhlafi HM, Anuar TS, Al-Adhroey AH, Atroosh WM, et al.
    Trop Med Int Health, 2017 04;22(4):493-504.
    PMID: 28151567 DOI: 10.1111/tmi.12848
    OBJECTIVES: To investigate the molecular epidemiology of Entamoeba histolytica, E. dispar and E. moshkovskii infections among rural communities in Yemen.

    METHODS: In a community-based study, faecal samples were collected from 605 participants and examined by wet mount, formalin-ether sedimentation, trichrome staining and nested multiplex PCR techniques. Demographic, socio-economic and environmental information was collected using a pre-tested questionnaire.

    RESULTS: Overall, 324 (53.6%) of the samples were positive for Entamoeba cysts and/or trophozoites by microscopic examination. Molecular analysis revealed that 20.2%, 15.7% and 18.2% of the samples were positive for E. histolytica, E. dispar and E. moshkovskii, respectively. Multivariate analysis showed different sets of species-specific risk factors among these communities. Educational level was identified as the significant risk factor for E. histolytica; age and gender were the significant risk factors for E. moshkovskii; and sources of drinking water and consumption of unwashed vegetables were the significant risk factors for E. dispar. Moreover, living in coastal/foothill areas and presence of other infected family members were risk factors for both E. histolytica and E. moshkovskii infections.

    CONCLUSION: The study reveals that Entamoeba spp. infection is highly prevalent among rural communities in Yemen, with E. histolytica, E. dispar and E. moshkovskii differentiated for the first time. Identifying and treating infected family members, providing health education pertinent to good personal and food hygiene practices and providing clean drinking water should be considered in developing a strategy to control intestinal parasitic infections in these communities, particularly in the coastal/foothill areas of the country.

  20. Barber BE, Russell B, Grigg MJ, Zhang R, William T, Amir A, et al.
    Blood Adv, 2018 02 27;2(4):433-443.
    PMID: 29487058 DOI: 10.1182/bloodadvances.2017013730
    The simian parasite Plasmodium knowlesi can cause severe and fatal human malaria. However, little is known about the pathogenesis of this disease. In falciparum malaria, reduced red blood cell deformability (RBC-D) contributes to microvascular obstruction and impaired organ perfusion. In P knowlesi infection, impaired microcirculatory flow has been observed in Macaca mulatta (rhesus macaques), unnatural hosts who develop severe and fatal disease. However, RBC-D has not been measured in human infection or in the natural host M fascicularis (long-tailed macaques). Using ektacytometry, we measured RBC-D in adults with severe and non-severe knowlesi and falciparum malaria and in healthy controls. In addition, we used micropipette aspiration to determine the relative stiffness of infected RBCs (iRBCs) and uninfected RBCs (uRBCs) in P knowlesi-infected humans and M fascicularis Ektacytometry demonstrated that RBC-D overall was reduced in human knowlesi malaria in proportion to disease severity, and in severe knowlesi malaria, it was comparable to that of severe falciparum malaria. RBC-D correlated inversely with parasitemia and lactate in knowlesi malaria and HRP2 in falciparum malaria, and it correlated with hemoglobin nadir in knowlesi malaria. Micropipette aspiration confirmed that in humans, P knowlesi infection increased stiffness of both iRBCs and uRBCs, with the latter mostly the result of echinocytosis. In contrast, in the natural host M fascicularis, echinocyte formation was not observed, and the RBC-D of uRBCs was unaffected. In unnatural primate hosts of P knowlesi, including humans, reduced deformability of iRBCs and uRBCs may represent a key pathogenic mechanism leading to microvascular accumulation, impaired organ perfusion, and anemia.
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