Displaying publications 1 - 20 of 131 in total

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  1. Aziz S, Ngui R, Lim YA, Sholehah I, Nur Farhana J, Azizan AS, et al.
    Trop Biomed, 2012 Mar;29(1):113-20.
    PMID: 22543611 MyJurnal
    In the last few years in Malaysia, dengue fever has increased dramatically and has caused huge public health concerns. The present study aimed to establish a spatial distribution of dengue cases in the city of Kuala Lumpur using a combination of Geographic Information System (GIS) and spatial statistical tools. Collation of data from 1,618 dengue cases in 2009 was obtained from Kuala Lumpur City Hall (DBKL). These data were processed and then converted into GIS format. Information on the average monthly rainfall was also used to correlate with the distribution pattern of dengue cases. To asses the spatial distribution of dengue cases, Average Nearest Neighbor (ANN) Analysis was applied together with spatial analysis with the ESRI ArcGIS V9.3 programme. Results indicated that the distribution of dengue cases in Kuala Lumpur for the year 2009 was spatially clustered with R value less than 1 (R = 0.42; z-scores = - 4.47; p < 0.001). Nevertheless, when this pattern was further analyzed according to month by each zone within Kuala Lumpur, two distinct patterns were observed which include a clustered pattern (R value < 1) between April to June and a dispersed pattern (R value > 1) between August and November. In addition, the mean monthly rainfall has not influenced the distribution pattern of the dengue cases. Implementation of control measures is more difficult for dispersed pattern compared to clustered pattern. From this study, it was found that distribution pattern of dengue cases in Kuala Lumpur in 2009 was spatially distributed (dispersed or clustered) rather than cases occurring randomly. It was proven that by using GIS and spatial statistic tools, we can determine the spatial distribution between dengue and population. Utilization of GIS tools is vital in assisting health agencies, epidemiologist, public health officer, town planner and relevant authorities in developing efficient control measures and contingency programmes to effectively combat dengue fever.
  2. Lau SM, Chua TH, Sulaiman WY, Joanne S, Lim YA, Sekaran SD, et al.
    Parasit Vectors, 2017 Mar 21;10(1):151.
    PMID: 28327173 DOI: 10.1186/s13071-017-2091-y
    BACKGROUND: Dengue remains a serious public health problem in Southeast Asia and has increased 37-fold in Malaysia compared to decades ago. New strategies are urgently needed for early detection and control of dengue epidemics.

    METHODS: We conducted a two year study in a high human density dengue-endemic urban area in Selangor, where Gravid Ovipositing Sticky (GOS) traps were set up to capture adult Aedes spp. mosquitoes. All Aedes mosquitoes were tested using the NS1 dengue antigen test kit. All dengue cases from the study site notified to the State Health Department were recorded. Weekly microclimatic temperature, relative humidity (RH) and rainfall were monitored.

    RESULTS: Aedes aegypti was the predominant mosquito (95.6%) caught in GOS traps and 23% (43/187 pools of 5 mosquitoes each) were found to be positive for dengue using the NS1 antigen kit. Confirmed cases of dengue were observed with a lag of one week after positive Ae. aegypti were detected. Aedes aegypti density as analysed by distributed lag non-linear models, will increase lag of 2-3 weeks for temperature increase from 28 to 30 °C; and lag of three weeks for increased rainfall.

    CONCLUSION: Proactive strategy is needed for dengue vector surveillance programme. One method would be to use the GOS trap which is simple to setup, cost effective (below USD 1 per trap) and environmental friendly (i.e. use recyclable plastic materials) to capture Ae. aegypti followed by a rapid method of detecting of dengue virus using the NS1 dengue antigen kit. Control measures should be initiated when positive mosquitoes are detected.

  3. Lau SM, Vythilingam I, Doss JI, Sekaran SD, Chua TH, Wan Sulaiman WY, et al.
    Trop Med Int Health, 2015 Oct;20(10):1271-80.
    PMID: 26094839 DOI: 10.1111/tmi.12555
    To determine the effectiveness of using sticky traps and the NS1 dengue antigen kit for the surveillance of Aedes mosquitoes for dengue control.
  4. Teh CS, Chua KH, Lim YA, Lee SC, Thong KL
    ScientificWorldJournal, 2014;2014:457839.
    PMID: 24967435 DOI: 10.1155/2014/457839
    We have successfully developed a Loop-mediated isothermal amplification (LAMP) assay that could specifically detect generic Escherichia coli (E. coli). This assay was tested on 85 bacterial strains and successfully identified 54 E. coli strains (average threshold time, Tt = 21.26). The sensitivity of this assay was evaluated on serial dilutions of bacterial cultures and spiked faeces. The assay could detect 10(2) CFU/mL for bacterial culture with Tt = 33.30 while the detection limit for spiked faeces was 10(3) CFU/mL (Tt = 31.12). We have also detected 46 generic E. coli from 50 faecal samples obtained from indigenous individuals with 16% of the positive samples being verocytotoxin-producing E. coli (VTEC) positive. VT1/VT2 allele was present in one faecal sample while the ratio of VT1 to VT2 was 6 : 1. Overall, our study had demonstrated high risk of VTEC infection among the indigenous community and most of the asymptomatic infection occurred among those aged below 15 years. The role of asymptomatic human carriers as a source of dissemination should not be underestimated. Large scale screening of the VTEC infection among indigenous populations and the potential contamination sources will be possible and easy with the aid of this newly developed rapid and simple LAMP assay.
  5. Uni S, Fukuda M, Ogawa K, Lim YA, Agatsuma T, Bunchom N, et al.
    Parasitol Int, 2017 Oct;66(5):593-595.
    PMID: 28648713 DOI: 10.1016/j.parint.2017.06.006
    An 11-year-old boy living in Otsu City, Shiga Prefecture, Kansai Region, Western Honshu, Japan had zoonotic onchocercosis. The patient developed a painful swelling on the little finger of his left hand. The worm detected in the excised mass had external transverse ridges but did not have inner striae in the cuticle. On the basis of the parasite's histopathological characteristics, the causative agent was identified as a female Onchocerca dewittei japonica (Spirurida: Onchocercidae). The species of the filarial parasite was confirmed by sequencing the cox1 gene of the parasite. The Japanese wild boar Sus scrofa leucomystax is a definitive host for O. dewittei japonica, which is then transmitted by blackflies as the vector to humans. The current case described occurred in the Kansai Region, Western Honshu, where such infections were previously not reported.
  6. Choy SH, Al-Mekhlafi HM, Mahdy MA, Nasr NN, Sulaiman M, Lim YA, et al.
    Sci Rep, 2014;4:6909.
    PMID: 25366301 DOI: 10.1038/srep06909
    This study was carried out to investigate the prevalence and risk factors of Giardia infection among indigenous people in rural Malaysia. Faecal samples were collected from 1,330 participants from seven states of Malaysia and examined by wet mount and formalin-ether sedimentation methods while demographic, socioeconomic and environmental information was collected using a pre-tested questionnaire. The overall prevalence of Giardia infection was 11.6% and was significantly higher among those aged ≤ 12 years compared to their older counterparts. Multivariate logistic regression identified age of ≤ 12 years, lacking of toilet at household, not washing hands before eating, not washing hands after playing with animals, not boiling water before consumption, bathing in the river, and not wearing shoes when outside as the significant risk factors of Giardia infection among these communities. Based on a multilocus genotyping approach (including tpi, gdh and bg gene sequences), 69 isolates were identified as assemblage A, and 69 as assemblage B. No association between the assemblages and presence of symptoms was found. Providing proper sanitation, as well as provision of clean drinking water and proper health education regarding good personal hygiene practices will help significantly in reducing the prevalence and burden of Giardia infection in these communities.
  7. Sady H, Al-Mekhlafi HM, Mahdy MA, Lim YA, Mahmud R, Surin J
    PLoS Negl Trop Dis, 2013;7(8):e2377.
    PMID: 23991235 DOI: 10.1371/journal.pntd.0002377
    BACKGROUND: Schistosomiasis, one of the most prevalent neglected tropical diseases, is a life-threatening public health problem in Yemen especially in rural communities. This cross-sectional study aims to determine the prevalence and associated risk factors of schistosomiasis among children in rural Yemen.

    METHODS/FINDINGS: Urine and faecal samples were collected from 400 children. Urine samples were examined using filtration technique for the presence of Schistosoma haematobium eggs while faecal samples were examined using formalin-ether concentration and Kato Katz techniques for the presence of S. mansoni. Demographic, socioeconomic and environmental information were collected via a validated questionnaire. Overall, 31.8% of the participants were found to be positive for schistosomiasis; 23.8% were infected with S. haematobium and 9.3% were infected with S. mansoni. Moreover, 39.5% of the participants were anaemic whereas 9.5% had hepatosplenomegaly. The prevalence of schistosomiasis was significantly higher among children aged >10 years compared to those aged ≤ 10 years (P<0.05). Multivariate analysis confirmed that presence of other infected family member (P<0.001), low household monthly income (P = 0.003), using unsafe sources for drinking water (P = 0.003), living nearby stream/spring (P = 0.006) and living nearby pool/pond (P = 0.002) were the key factors significantly associated with schistosomiasis among these children.

    CONCLUSIONS/SIGNIFICANCE: This study reveals that schistosomiasis is still highly prevalent in Yemen. These findings support an urgent need to start an integrated, targeted and effective schistosomiasis control programme with a mission to move towards the elimination phase. Besides periodic drug distribution, health education and community mobilisation, provision of clean and safe drinking water, introduction of proper sanitation are imperative among these communities in order to curtail the transmission and morbidity caused by schistosomiasis. Screening and treating other infected family members should also be adopted by the public health authorities in combating this infection in these communities.

  8. Huey CS, Mahdy MA, Al-Mekhlafi HM, Nasr NA, Lim YA, Mahmud R, et al.
    Infect Genet Evol, 2013 Jul;17:269-76.
    PMID: 23624189 DOI: 10.1016/j.meegid.2013.04.013
    Giardia duodenalis is considered the most common intestinal parasite in humans worldwide. In Malaysia, many studies have been conducted on the epidemiology of giardiasis. However, there is a scarcity of information on the genetic diversity and the dynamics of transmission of G. duodenalis. The present study was conducted to identify G. duodenalis assemblages and sub-assemblages based on multilocus analysis of the glutamate dehydrogenase (gdh), beta-giardin (bg) and triose phosphate isomerase (tpi) genes. Faecal specimens were collected from 484 Orang Asli children with a mean age of 7 years and examined using light microscopy. Specimens positive for Giardia were subjected to PCR analysis of the three genes and subsequent sequencing in both directions. Sequences were edited and analysed by phylogenetic analysis. G. duodenalis was detected in 17% (84 of 484) of the examined specimens. Among them, 71 were successfully sequenced using at least one locus. Genotyping results showed that 30 (42%) of the isolates belonged to assemblage A, 32 (45%) belonged to assemblage B, while discordant genotype results were observed in 9 specimens. Mixed infections were detected in 43 specimens using a tpi-based assemblage specific protocol. At the sub-assemblages level, isolates belonged to assemblage A were AII. High nucleotide variation found in isolates of assemblage B made subtyping difficult to achieve. The finding of assemblage B and the anthroponotic genotype AII implicates human-to-human transmission as the most possible mode of transmission among Malaysian aborigines. The high polymorphism found in isolates of assemblage B warrants a more defining tool to discriminate assemblage B at the sub-assemblage level.
  9. Mahdy MA, Lim YA, Ngui R, Siti Fatimah MR, Choy SH, Yap NJ, et al.
    Parasit Vectors, 2012;5:88.
    PMID: 22564445 DOI: 10.1186/1756-3305-5-88
    Canine hookworm infection is endemic in Southeast Asian countries with a prevalence ranging from 70% to 100%, with zoonotic transmission representing a potentially significant public health concern. However, there are limited data available on the prevalence of canine hookworms in Malaysia. This study was conducted to determine the prevalence of hookworm and Ancylostoma species among dogs in Malaysia.
  10. Al-Mekhlafi MS, Atiya AS, Lim YA, Mahdy AK, Ariffin WA, Abdullah HC, et al.
    PMID: 18613540
    Despite great development in socioeconomic status throughout 50 years of independence, Malaysia is still plagued with soil-transmitted helminthiases (STH). STH continue to have a significant impact on public health particularly in rural communities. In order to determine the prevalence of STH among rural Orang Asli children and to investigate the possible risk factors affecting the pattern of this prevalence, fecal samples were collected from 292 Orang Asli primary schoolchildren (145 males and 147 females) age 7-12 years, from Pos Betau, Kuala Lipis, Pahang. The samples were examined by Kato-Katz and Harada Mori techniques. Socioeconomic data were collected using pre-tested questionnaires. The overall prevalence of ascariasis, trichuriasis, and hookworm infections were 67.8, 95.5 and 13.4%, respectively. Twenty-nine point eight percent of the children had heavy trichuriasis, while 22.3% had heavy ascariasis. Sixty-seven point seven percent of the children had mixed infections. Age > 10 years (p = 0.016), no toilet in the house (p = 0.012), working mother (p = 0.040), low household income (p = 0.033), and large family size (p = 0.028) were identified as risk factors for ascariasis. Logistic regression confirmed low income, no toilet in the house and working mother as significant risk factors for ascariasis. The prevalence of STH is still very high in rural Malaysian communities. STH may also contribute to other health problems such as micronutrient deficiencies, protein-energy malnutrition and poor educational achievement. Public health personnel need to reassess current control measures and identify innovative and integrated ways in order to reduce STH significantly in rural communities.
  11. Sady H, Al-Mekhlafi HM, Webster BL, Ngui R, Atroosh WM, Al-Delaimy AK, et al.
    Parasit Vectors, 2015;8:544.
    PMID: 26482435 DOI: 10.1186/s13071-015-1168-8
    Human schistosomiasis is a neglected tropical disease of great importance that remains highly prevalent in Yemen, especially amongst rural communities. In order to investigate the genetic diversity of human Schistosoma species, a DNA barcoding study was conducted on S. mansoni and S. haematobium in Yemen.
  12. Sady H, Al-Mekhlafi HM, Ngui R, Atroosh WM, Al-Delaimy AK, Nasr NA, et al.
    Int J Mol Sci, 2015;16(7):16085-103.
    PMID: 26193254 DOI: 10.3390/ijms160716085
    The present study describes a real-time PCR approach with high resolution melting-curve (HRM) assay developed for the detection and differentiation of Schistosoma mansoni and S. haematobium in fecal and urine samples collected from rural Yemen. The samples were screened by microscopy and PCR for the Schistosoma species infection. A pair of degenerate primers were designed targeting partial regions in the cytochrome oxidase subunit I (cox1) gene of S. mansoni and S. haematobium using real-time PCR-HRM assay. The overall prevalence of schistosomiasis was 31.8%; 23.8% of the participants were infected with S. haematobium and 9.3% were infected with S. mansoni. With regards to the intensity of infections, 22.1% and 77.9% of S. haematobium infections were of heavy and light intensities, respectively. Likewise, 8.1%, 40.5% and 51.4% of S. mansoni infections were of heavy, moderate and light intensities, respectively. The melting points were distinctive for S. mansoni and S. haematobium, categorized by peaks of 76.49 ± 0.25 °C and 75.43 ± 0.26 °C, respectively. HRM analysis showed high detection capability through the amplification of Schistosoma DNA with as low as 0.0001 ng/µL. Significant negative correlations were reported between the real-time PCR-HRM cycle threshold (Ct) values and microscopic egg counts for both S. mansoni in stool and S. haematobium in urine (p < 0.01). In conclusion, this closed-tube HRM protocol provides a potentially powerful screening molecular tool for the detection of S. mansoni and S. haematobium. It is a simple, rapid, accurate, and cost-effective method. Hence, this method is a good alternative approach to probe-based PCR assays.
  13. Al-Mekhlafi HM, Al-Maktari MT, Jani R, Ahmed A, Anuar TS, Moktar N, et al.
    PLoS Negl Trop Dis, 2013;7(10):e2516.
    PMID: 24205426 DOI: 10.1371/journal.pntd.0002516
    Giardia duodenalis infection and malnutrition are still considered as public health problems in many developing countries especially among children in rural communities. This study was carried out among Aboriginal (Orang Asli) primary schoolchildren in rural peninsular Malaysia to investigate the burden and the effects of Giardia infection on growth (weight and height) of the children.
  14. Roslan MA, Shafie A, Ngui R, Lim YA, Sulaiman WY
    J Am Mosq Control Assoc, 2013 Dec;29(4):328-36.
    PMID: 24551965
    Dengue is a serious public health problem in Malaysia. The aim of this study was to compare the vertical infestation of Aedes population in 2 apartments in Kuala Lumpur with different status of dengue incidence (i.e., high-dengue-incidence area and area with no reported dengue cases). The study was also conducted to assess the relationship between environmental factors such as rainfall, temperature, and humidity and Aedes population that may influence Aedes infestation. Surveillance with a mosquito larvae trapping device was conducted for 28 continuous weeks (January to July 2012) in Vista Angkasa (VA) and Inderaloka (IL) apartments located in Kuala Lumpur, Malaysia. The results indicated that both Aedes spp. could be found from ground to higher floor levels of the apartments, with Aedes aegypti being more predominant than Ae. albopictus. Data based on mixed and single breeding of Aedes spp. on different floors did not show any significant difference. Both rainfall (R3; i.e., the amount of rainfall collected during the previous 3 wk before the surveillance period began) and RH data showed significant relationship with the number of Aedes larvae collected in VA and IL. No significant difference was found between the numbers of Aedes larvae in both study areas as well as maximum and minimum temperatures. Results also indicated adaptations of Ae. aegypti to the ecosystem at each elevation of high-rise buildings, with Ae. albopictus staying inside of apartment units.
  15. Shafie A, Roslan MA, Ngui R, Lim YA, Sulaiman WY
    J Am Mosq Control Assoc, 2016 Dec;32(4):273-281.
    PMID: 28206867 DOI: 10.2987/16-6604.1
    Mosquito-borne diseases have been increasing at an alarming rate over the past decades. In Malaysia, one finds several important mosquito-borne diseases such as Japanese encephalitis, dengue, malaria, and chikungunya. Mosquito surveillance and control programs are the most effective way of detecting and controlling mosquito-borne diseases, but these programs are less effective without an aware and well-informed general public. In 2014 we used a questionnaire to evaluate the extent of awareness of basic mosquito biology and mosquito-borne diseases in 6 villages, Kampung Masjid, Kampung Teluk Gedung, Kampung Teluk Dalam, Kampung Ujung Kelawai, Kampung Sungai Pinang Besar, and Kampung Sungai Pinang Kechil on Pangkor Island, Malaysia. A total of 1,012 individuals responded to the questionnaire, consisting of 790 Malay (78.1%), 164 Chinese (16.2%), and 58 Indian (5.7%). More than 60% (Malay = 73.7%, Chinese = 64.0%, Indian = 79.3%) of the respondents were familiar with basic mosquito biology and practiced personal protection against mosquito bites, and the association was statistically significant (P = 0.02). However, the majority of the respondents had limited knowledge on mosquito-borne diseases, and this varied significantly among the 3 ethnic groups (P = 0.0001). Our recommendations are to improve and intensify public health education outreach programs to the island residents and to encourage community participation in vector control programs.
  16. Low VL, Adler PH, Takaoka H, Ya'cob Z, Lim PE, Tan TK, et al.
    PLoS One, 2014;9(6):e100512.
    PMID: 24941043 DOI: 10.1371/journal.pone.0100512
    The population genetic structure of Simulium tani was inferred from mitochondria-encoded sequences of cytochrome c oxidase subunits I (COI) and II (COII) along an elevational gradient in Cameron Highlands, Malaysia. A statistical parsimony network of 71 individuals revealed 71 haplotypes in the COI gene and 43 haplotypes in the COII gene; the concatenated sequences of the COI and COII genes revealed 71 haplotypes. High levels of genetic diversity but low levels of genetic differentiation were observed among populations of S. tani at five elevations. The degree of genetic diversity, however, was not in accordance with an altitudinal gradient, and a Mantel test indicated that elevation did not have a limiting effect on gene flow. No ancestral haplotype of S. tani was found among the populations. Pupae with unique structural characters at the highest elevation showed a tendency to form their own haplotype cluster, as revealed by the COII gene. Tajima's D, Fu's Fs, and mismatch distribution tests revealed population expansion of S. tani in Cameron Highlands. A strong correlation was found between nucleotide diversity and the levels of dissolved oxygen in the streams where S. tani was collected.
  17. Low VL, Chen CD, Lim PE, Lee HL, Tan TK, Lim YA, et al.
    Pestic Biochem Physiol, 2013 Sep;107(1):127-31.
    PMID: 25149246 DOI: 10.1016/j.pestbp.2013.06.004
    A nationwide investigation was performed to detect the presence of 1014 mutation(s) in voltage gated sodium channel (kdr) gene of Culex quinquefasciatus from 14 residential areas across 13 states and a federal territory in Malaysia. Molecular genotyping of kdr mutation was performed via a modified three tubes allele-specific-polymerase chain reaction (AS-PCR) and direct sequencing of kdr gene. Based on the results of AS-PCR, homozygous susceptible (SS) genotype was found in nine out of 14 populations with 38 individuals from a total sample size of 140. Heterozygous (RS) genotype was most predominant (99 individuals) and distributed across all study sites. Homozygous resistance (RR) genotype was detected in Perak (one individual) and Selangor (two individuals). The resistance kdr allele frequencies ranged from 0.1 to 0.55, with the highest being detected in Cx. quinquefasciatus population from Selangor. This study has documented the first field-evolved instance of 1014F mutation in Malaysian mosquitoes and the findings of this study could be utilized in the implementation of strategic measures in vector control programs in Malaysia.
  18. Low VL, Tan TK, Lim PE, Domingues LN, Tay ST, Lim YA, et al.
    Vet Parasitol, 2014 Aug 29;204(3-4):439-42.
    PMID: 24912955 DOI: 10.1016/j.vetpar.2014.05.036
    A multilocus sequence analysis using mitochondria-encoded cytochrome c oxidase subunit I (COI), cytochrome B (CytB), NADH dehydrogenase subunit 5 (ND5); nuclear encoded 18S ribosomal RNA (18S) and 28S ribosomal RNA (28S) genes was performed to determine the levels of genetic variation between the closely related species Haematobia irritans Linnaeus and Haematobia exigua de Meijere. Among these five genes, ND5 and CytB genes were found to be more variable and informative in resolving the interspecific relationships of both species. In contrast, the COI gene was more valuable in inferring the intraspecific relationships. The ribosomal 18S and 28S sequences of H. irritans and H. exigua were highly conserved with limited intra- and inter-specific variation. Molecular evidence presented in this study demonstrated that both flies are genetically distinct and could be differentiated based on sequence analysis of mitochondrial genes.
  19. Low VL, Chen CD, Lee HL, Tan TK, Chen CF, Leong CS, et al.
    PLoS One, 2013;8(11):e79928.
    PMID: 24278220 DOI: 10.1371/journal.pone.0079928
    There has been no comprehensive study on biochemical characterization of insecticide resistance mechanisms in field populations of Malaysian Culex quinquefasciatus. To fill this void in the literature, a nationwide investigation was performed to quantify the enzyme activities, thereby attempting to characterize the potential resistance mechanisms in Cx. quinquefasciatus in residential areas in Malaysia.
  20. Low VL, Tay ST, Kho KL, Koh FX, Tan TK, Lim YA, et al.
    Parasit Vectors, 2015;8:341.
    PMID: 26104478 DOI: 10.1186/s13071-015-0956-5
    The morphotaxonomy of Rhipicephalus microplus complex has been challenged in the last few years and prompted many biologists to adopt a DNA-based method for distinguishing the members of this group. In the present study, we used a mitochondrial DNA analysis to characterise the genetic assemblages, population structure and dispersal pattern of R. microplus from Southeast Asia, the region where the species originated.
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