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Fulltext Low efficacy of delthamethrin-treated net against Singapore Aedes aegypti is associated with kdr-type resistance

Pang SC, Chiang LP, Tan CH, Vythilingam I, Lam-Phua SG, Ng LC

Trop Biomed, 2015 Mar;32(1):140-50.
PMID: 25801264 MyJurnal

There has been a worldwide surge in the number and severity of dengue in the past decades. In Singapore, relentless vector control efforts have been put in to control the disease since the 1960's. Space spraying, fogging, chemical treatment and source reduction are some commonly used methodologies for controlling its vectors, particularly Aedes aegypti. Here, as we explored the use of a commercially available delthamethrin-treated net as an alternative strategy and the efficacy of the treated net was found to be limited. Through bioassays and molecular studies, the failure of the treated net to render high mortality rate was found to be associated with the knockdown resistance (kdr) mutation. This is the first report of kdr- mutations in Singapore's Ae. aegypti. At least one point mutation, either homozygous or heterozygous, at amino acid residue V1016G of DIIS6 or F1269C of DIIIS6 was detected in 93% of field strains of Ae. aegypti. Various permutations of wild type and mutant amino acids of the four alleles were found to result in varying degree of survival rate among local field Ae. aegypti when exposed to the deltamethrin treated net. Together with the association of higher survival rate with the presence of both V1016G and F1269C, the data suggest the role of these mutations in the resistance to the deltamethrin. The high prevalence of these mutations were confirmed in a country wide survey where 70% and 72% of the 201 Ae. aegypti analysed possessed the mutations at residues 1016 and 1269 respectively. The highest mutated frequency combination was found to be heterozygous alleles (VG/FC) at both residues 1016 and 1269 (37.8%), followed by homozygous mutation at allele 1269 (24.4%) and homozygous mutation at allele 1016 (22.9%). The kdr- type of resistance among the vector is likely to undermine the effectiveness of pyrethroids treated materials against these mosquitoes.
Fulltext Screening of antiviral activities in medicinal plants extracts against dengue virus using dengue NS2B-NS3 protease assay

Rothan HA, Zulqarnain M, Ammar YA, Tan EC, Rahman NA, Yusof R

Trop Biomed, 2014 Jun;31(2):286-96.
PMID: 25134897 MyJurnal

Dengue virus infects millions of people worldwide and there is no vaccine or anti-dengue therapeutic available. Screening large numbers of medicinal plants for anti-dengue activities is an alternative strategy in order to find the potent therapeutic compounds. Therefore, this study was designed to identify anti-dengue activities in nineteen medicinal plant extracts that are used in traditional medicine. Local medicinal plants Vernonia cinerea, Hemigraphis reptans, Hedyotis auricularia, Laurentia longiflora, Tridax procumbers and Senna angustifolia were used in this study. The highest inhibitory activates against dengue NS2B-NS3pro was observed in ethanolic extract of S. angustifolia leaves, methanolic extract of V. cinerea leaves and ethanol extract of T. procumbens stems. These findings were further verified by in vitro viral inhibition assay. Methanolic extract of V. cinerea leaves, ethanol extract of T. procumbens stems and at less extent ethanolic extract of S. angustifolia leaves were able to maintain the normal morphology of DENV2-infected Vero cells without causing much cytopathic effects (CPE). The percentage of viral inhibition of V. cinerea and T. procumbens extracts were significantly higher than S. angustifolia extract as measured by plaque formation assay and RT-qPCR. In conclusion, The outcome of this study showed that the methanolic extract of V. cinerea leaves and ethanol extract of T. procumbens stems possessed high inhibitory activates against dengue virus that worth more investigation.
Fulltext Efficacies of two in-house indirect ELISAs for diagnosis of amoebic liver abscess

Tan ZN, Wong WK, Noordin R, Zeehaida M, Olivos GA, Lim BH

Trop Biomed, 2013 Jun;30(2):250-6.
PMID: 23959490 MyJurnal

Entamoeba histolytica causes amoebic diarrhoea, colitis and liver abscess (ALA). Diagnosis of ALA is difficult, as most patients do not have simultaneous intestinal amoebic infection. At Hospital Universiti Sains Malaysia (HUSM), diagnosis of ALA relies on a combination of clinical findings, ultrasound examination of the liver and serodiagnosis using a commercial kit. In this study, two in-house indirect ELISAs were developed and evaluated. One of the in-house assays utilises E. histolytica crude soluble antigen (CSA) to detect serum IgG specific to the parasite whereas the other uses E. histolytica ether extract antigen (EEA). Preparation of CSA requires a sonicator to lyse the amoeba whereas EEA was prepared by chemically solubilizing the trophozoites. Based on the cut-off value of mean optical density + 3SD, CSA-ELISA showed 100% (24/24) sensitivity and 93.33% (210/225) specificity; while EEA-ELISA showed 91.67% (22/24) sensitivity and 95.11% (214/225) specificity. In conclusion, both the in-house indirect ELISAs were found to be efficacious for diagnosis of ALA; and the EEA is easier to prepare than the commonly used CSA.
Fulltext Recombinant proteins from new constructs of SAG1 and GRA7 sequences and their usefulness to detect acute toxoplasmosis

Kotresha D, Poonam D, Muhammad Hafiznur Y, Saadatnia G, Nurulhasanah O, Sabariah O, et al.

Trop Biomed, 2012 Mar;29(1):129-37.
PMID: 22543613 MyJurnal

In this study we have cloned unreported gene fragments of Toxoplasma gondii GRA7 and SAG1 and expressed the corresponding recombinant proteins, followed by evaluation of their usefulness for the serological diagnosis of toxoplasmosis. Both recombinant proteins were expressed efficiently in insoluble form, purified by single step Ni-NTA affinity chromatography and their antigenicity to detect toxoplasma specific IgG antibodies were determined by immunoblotting. A total of 60 serum samples from three groups of individuals based on their anti-toxoplasma antibody profiles were tested, namely (I) IgM+, IgG+ (n=20), (II) IgM-, IgG+ (n=20) and (III) IgM-, IgG- (n=20). Both recombinant proteins exhibited high sensitivity (100%) with sera from Group I. rGRA7 and rSAG1 reacted 40% and 80% respectively with Group II sera. The specificity of the recombinant proteins based on reactivities with Group III sera were 100% and 80% with rGRA7 and rSAG1 respectively. Thus rGRA7 was found to be better at discriminating probable acute from chronic phases of toxoplasmosis, and it also showed higher specificity.
Fulltext Penicilliosis in lupus patients presenting with unresolved fever: a report of 2 cases and literature review

Chong YB, Tan LP, Robinson S, Lim SK, Ng KP, Keng TC, et al.

Trop Biomed, 2012 Jun;29(2):270-6.
PMID: 22735849 MyJurnal

Penicilliosis is a rare occurrence among non human immunodeficiency virus (HIV) infected patients. We report here two cases of Penicillium marneffei infection in patients with systemic lupus erythematosus (SLE). Both patients had a recent flare of lupus and were on immunosuppressive drugs when they presented with prolonged fever without an obvious foci of infection, unresponsive to broad-spectrum antibiotics. They were leucopaenic upon admission, with rapid deterioration during the course of the illness. Diagnosis of penicilliosis via fungal isolation from blood culture was delayed resulting in the late initiation of antifungal agents. While both patients ultimately recovered, the delay in diagnosis led to a prolonged hospital stay with increased morbidity. Clinicians should be aware of this uncommon but emerging fungal pathogen in SLE patients and maintain a high index of suspicion in diagnosing this potentially fatal but treatable disease.
Fulltext Optimal protein extraction methods from diverse sample types for protein profiling by using Two-Dimensional Electrophoresis (2DE)

Tan AA, Azman SN, Abdul Rani NR, Kua BC, Sasidharan S, Kiew LV, et al.

Trop Biomed, 2011 Dec;28(3):620-9.
PMID: 22433892 MyJurnal

There is a great diversity of protein samples types and origins, therefore the optimal procedure for each sample type must be determined empirically. In order to obtain a reproducible and complete sample presentation which view as many proteins as possible on the desired 2DE gel, it is critical to perform additional sample preparation steps to improve the quality of the final results, yet without selectively losing the proteins. To address this, we developed a general method that is suitable for diverse sample types based on phenolchloroform extraction method (represented by TRI reagent). This method was found to yield good results when used to analyze human breast cancer cell line (MCF-7), Vibrio cholerae, Cryptocaryon irritans cyst and liver abscess fat tissue. These types represent cell line, bacteria, parasite cyst and pus respectively. For each type of samples, several attempts were made to methodically compare protein isolation methods using TRI-reagent Kit, EasyBlue Kit, PRO-PREP™ Protein Extraction Solution and lysis buffer. The most useful protocol allows the extraction and separation of a wide diversity of protein samples that is reproducible among repeated experiments. Our results demonstrated that the modified TRI-reagent Kit had the highest protein yield as well as the greatest number of total proteins spots count for all type of samples. Distinctive differences in spot patterns were also observed in the 2DE gel of different extraction methods used for each type of sample.
Fulltext Unusual manifestation of cutaneous toxoplasmosis in a HIV-positive patient

Fong MY, Wong KT, Rohela M, Tan LH, Adeeba K, Lee YY, et al.

Trop Biomed, 2010 Dec;27(3):447-50.
PMID: 21399585 MyJurnal

We report a case of unusual cutaneous toxoplasmosis manifestation in a HIV-positive patient. He presented with hard and painful nodular lesions on the arms, hands and chest. Serology tests for anti-Toxoplasma antibody were negative. However, histopathologic examination of the lesion revealed foci of macrophages containing crescent-shaped organisms resembling the zoites of the protozoan parasite Toxoplasma gondii. Ultrastructure examination under electron microscopy and PCR confirmed the organism as T. gondii.
Fulltext New mosquito species records (Diptera: Culicidae) from Singapore

Jeffery J, Lee RM, Tan SY, Liew C, Ng LC, Lam-Phua SG

Trop Biomed, 2010 Apr;27(1):138-42.
PMID: 20562825

Nine species of mosquitoes in eight genera are recorded for the first time in Singapore. An additional two species were overlooked in a 1986 checklist for mosquitoes in Singapore, and one was described after 1986. Location and habitat data are provided for the nine new records. With the inclusion of these new records the number of species reported from Singapore is 137.
Fulltext The protective effects of Mucuna pruriens seed extract against histopathological changes induced by Malayan cobra (Naja sputatrix) venom in rats

Fung SY, Tan NH, Liew SH, Sim SM, Aguiyi JC

Trop Biomed, 2009 Apr;26(1):80-4.
PMID: 19696731

Seed of Mucuna pruriens (Velvet beans) has been prescribed by traditional medicine practitioners in Nigeria as a prophylactic oral antisnake remedy. In the present studies, we investigated the protective effects of M. pruriens seed extract (MPE) against histopathological changes induced by intravenous injection of Naja sputatrix (Malayan cobra) venom in rats pretreated with the seed extract. Examination by light microscope revealed that the venom induced histopathological changes in heart and blood vessels in liver, but no effect on brain, lung, kidney and spleen. The induced changes were prevented by pretreatment of the rats with MPE. Our results suggest that MPE pretreatment protects rat heart and liver blood vessels against cobra venom-induced damages.
Fulltext Sequence variation in the cytochrome oxidase subunit I and II genes of two commonly found blow fly species, Chrysomya megacephala (Fabricius) and Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae) in Malaysia

Tan SH, Aris EM, Surin J, Omar B, Kurahashi H, Mohamed Z

Trop Biomed, 2009 Aug;26(2):173-81.
PMID: 19901904

The mitochondiral DNA region encompassing the cytochrome oxidase subunit I (COI) and cytochrome oxidase subunit II (COII) genes of two Malaysian blow fly species, Chrysomya megacephala (Fabricius) and Chrysomya rufifacies (Macquart) were studied. This region, which spans 2303bp and includes the COI, tRNA leucine and partial COII was sequenced from adult fly and larval specimens, and compared. Intraspecific variations were observed at 0.26% for Ch. megacephala and 0.17% for Ch. rufifacies, while sequence divergence between the two species was recorded at a minimum of 141 out of 2303 sites (6.12%). Results obtained in this study are comparable to published data, and thus support the use of DNA sequence to facilitate and complement morphology-based species identification.
Fulltext A new record of Fannia prisca Stein, 1918 (Diptera:Fanniidae) from peninsular Malaysia

Heo CC, Kurahashi H, Nishida K, Tan Siew H, Mohamed Z, Mohamed AM, et al.

Trop Biomed, 2008 Dec;25(3):254-6.
PMID: 19287366

Fannia prisca Stein, 1918 is newly recorded from peninsular Malaysia. This record is based on 4 male specimens from Mount Berembun, Brinchang, Cameron Highland, Pahang state, peninsular Malaysia. It is previously recorded from China, Mongolia, Korea, Japan, Taiwan, Bonin Island, Thailand and oriental region. The male of Fannia prisca can be differentiated from male Fannia scalaris by the following features: for F. prisca, mid-coxa without spine; mid-tibia normal or without stout triangular ventral projection; and hind tibia usually with 2 av, while F. scalaris has several stout hook-like spines on the anterior margin; mid-tibia with stout triangular ventral projection and hind tibia usually with 3 av. Both F. prisca and F. scalaris can be differentiated from Fannia leucosticta by looking at its hind tibia, which only has 1 av.
DNA barcoding relates Trichuris species from a human and a man's best friend to non-human primate sources

Brandon-Mong GJ, Ketzis JK, Choy JS, Boonroumkaew P, Tooba M, Sawangjaroen N, et al.

Trop Biomed, 2018 Dec 01;35(4):1131-1139.
PMID: 33601860

Trichuris trichiura, the whipworm of humans, is one of the most prevalent soiltransmitted helminths (STH) reported worldwide. According to a recent study, out of 289 STH studies in Southeast Asia, only three studies used molecular methods. Hence, the genetic assemblages of Trichuris in Southeast Asia are poorly understood. In this study, we used partial mitochondrial DNA (cytochrome c oxidase subunit 1 or COI) sequences for analysis. Trichuris grouped in a same clade with different hosts indicate the potential of cross infection between hosts. Based on COI, the adult Trichuris isolated from a Malaysian patient was most closely related to Trichuris isolated from Papio anubis (olive baboons) from the USA. The Trichuris isolated from the dog from Malaysia was genetically similar to a Trichuris species isolated from Macaca silenus (lion-tailed macaque) from Czech Republic. Both the human and dog isolated Trichuris grouped in clades with different hosts indicating the potential of cross infection between hosts. Specific PCR primers based on the partial COI of T. trichiura isolated from African green monkey and T. serrata were designed and successfully amplified using multiplex PCR of the pooled DNA samples. Our results suggest a complex parasite-host relationship, and support the theory of cross infection of Trichuris between humans and non-human primates as suggested in previous publications.
Fulltext Revisiting Spasticity After Stroke: Clustering Clinical Characteristics for Identifying At-Risk Individuals

Ahmedy F, Mohd Tuah N, Mohamad Hashim N, Sybil Shah S, Ahmedy I, Tan SF

J Multidiscip Healthc, 2021;14:2391-2396.
PMID: 34511922 DOI: 10.2147/JMDH.S320543

Purpose: To collectively identify the clinical characteristics determining the risk of developing spasticity after stroke.
Patients and Methods: A cross-sectional study was conducted at a single rehabilitation outpatient clinic from June to December 2019. Inclusion criteria were stroke duration of over four weeks, aged 18 years and above. Exclusion criteria were presence of concurrent conditions other than stroke that could also lead to spasticity. Recruited patients were divided into "Spasticity" and "No spasticity" groups. Univariate analysis was deployed to identify significant predictive spasticity factors between the two groups followed by a two-step clustering approach for determining group of characteristics that collectively contributes to the risk of developing spasticity in the "Spasticity" group.
Results: A total of 216 post-stroke participants were recruited. The duration after stroke (p < 0.001) and the absence of hemisensory loss (p = 0.042) were two significant factors in the "Spasticity" group revealed by the univariate analysis. From a total of 98 participants with spasticity, the largest cluster of individuals (40 patients, 40.8%) was those within less than 20 months after stroke with moderate stroke and absence of hemisensory loss, while the smallest cluster was those within less than 20 months after severe stroke and absence of hemisensory loss (21 patients, 21.4%).
Conclusion: Analyzing collectively the significant factors of developing spasticity may have the potential to be more clinically relevant in a heterogeneous post-stroke population that may assist in the spasticity management and treatment.
Fulltext The Site of Airway Collapse in Sleep Apnea, Its Associations with Disease Severity and Obesity, and Implications for Mechanical Interventions

Sung CM, Tan SN, Shin MH, Lee J, Kim HC, Lim SC, et al.

Am J Respir Crit Care Med, 2021 07 01;204(1):103-106.
PMID: 33826879 DOI: 10.1164/rccm.202011-4266LE
First molecular detection of Tritrichomonas foetus in domestic cats in Klang Valley, Malaysia

Tan LP, Megat Abd Rani PA, Sharma RSK, Syed Hussain SS, Watanabe M

Trop Biomed, 2020 Sep 01;37(3):756-762.
PMID: 33612788 DOI: 10.47665/tb.37.3.756

Tritrichomonas foetus is known to cause chronic diarrhea in the feline species in many different regions of the world. However, there is a paucity of information on T. foetus among cats in Malaysia. This study was conducted to determine the prevalence of Tritrichomonas foetus in the pet and stray cat population in Klang Valley, Malaysia. A total of 201 pet and stray cats' fecal samples were collected in Klang Valley. 24 samples were cultured in the InPouch® TF Feline to observe for motile trophozoites. A nested PCR protocol was used to screen for T. foetus in the collected samples. The prevalence of T. foetus in the cat population in Klang Valley was 33%. There was no association between Tritrichomonas infection and age, sex, breed or management of the cats. However, statistical analysis revealed that stray cats were more likely to be infected with T. foetus compared to pet cats. This study confirmed for the first time the presence of T. foetus among the cat population in Klang Valley, Malaysia.
Prevalence of Toxoplasma gondii in pet and stray cats in Klang Valley, Malaysia

Tan LP, Megat Abd Rani PA, Sharma RSK, Syed Hussain SS, Watanabe M

Trop Biomed, 2020 Sep 01;37(3):542-550.
PMID: 33612769 DOI: 10.47665/tb.37.3.542

Toxoplasma gondii, a zoonotic protozoan that has a worldwide distribution, is known to infect many warm-blooded vertebrates. The feline species including domestic cats are the definitive hosts for Toxoplama gondii and shed the infective oocyst. There is lack of information on the prevalence of Toxoplasma gondii in cats in Malaysia. The objective of this study was to determine both the seroprevalence of T. gondii and the prevalence of T. gondii DNA in cats' feces in Klang Valley, Malaysia. 198 blood and 201 fecal samples were collected from pet and stray cats from the local council, Dewan Bandaraya Kuala Lumpur (DBKL) and University Veterinary Hospital, Universiti Putra Malaysia respectively. The overall seroprevalence of Toxoplasma gondii in cats in the Klang Valley was found to be 5.5%. There was a high prevalence (10.5%) of T. gondii DNA detected in the cat fecal samples in both pet and stray cats suggestive of T. gondii oocyst shedding. Stray cats showed a higher seroprevalence and molecular prevalence of T. gondii than the pet cats. However, comparative analysis using Chi-square test showed no significant difference between both groups (P>0.05). Higher prevalence (10.5%) of cats shedding T. gondii DNA as compared to the seroprevalence (5.5%) was found in the cat population in the Klang Valley. The high prevalence of cats shedding T. gondii DNA is alarming as this may directly reflect the number of oocysts excreted into the environment posing a significant public health hazard.
Effect of disaccharide-polyol systems on the thermal stability of freeze-dried Mycobacterium bovis

Tan YZ, Chong YQ, Khong E, Liew YK, Chieng N

Int J Pharm, 2019 Jul 20;566:400-409.
PMID: 31136777 DOI: 10.1016/j.ijpharm.2019.05.063

Live attenuated Mycobacterium bovis (M. bovis), marketed as Bacille Calmette-Guérin is the only FDA-approved vaccine against tuberculosis. The prerequisite of cold chain storage between 2 and 8 °C hinders the global vaccination effort. The study aims to investigate the effect of trehalose, sucrose and glycerol combinations in enhancing the stability of M. bovis. The bacilli were formulated in various ratios of trehalose-glycerol, sucrose-glycerol, trehalose-sucrose-glycerol systems (test samples) and sodium glutamate (control), freeze-dried and stored for 28 days at 4 °C, 25 °C and 37 °C. Bacteria viability at pre-, post-freeze-drying and after storage were quantified by its density in colony-forming unit per milliliter (CFU/mL) as obtained through the pour plate method. Formulations were characterized using differential scanning calorimetry. Structural collapsed cakes were found on all freeze-dried formulations because of the low Tg'. Comparing between binary and ternary formulations, trehalose-sucrose-glycerol was found to be a superior lyoprotectant. Upon storage, the viability of bacteria in disaccharide-polyol formulations was highest when stored at 4 °C followed by 25 °C. The lowest viability was found after storage at 37 °C. While the ternary disaccharide-polyol system may be used as a thermoprotectant up to 25 °C, sodium glutamate has a superior thermoprotective effect at temperature above 25 °C.
Relative bioavailability of the hydrochloride, sulphate and ethyl carbonate salts of quinine

Jamaludin A, Mohamad M, Navaratnam V, Selliah K, Tan SC, Wernsdorfer WH, et al.

Br J Clin Pharmacol, 1988 Feb;25(2):261-3.
PMID: 3358888

The hydrochloride, sulphate and ethylcarbonate salts of quinine were given in single oral doses (600 mg base equivalent) to nine healthy male subjects according to a cross-over design. No statistically significant differences were noted in the plasma drug concentration-time profiles although inter- and intra-subject variation in AUC, Cmax and tmax values was appreciable. The ethylcarbonate salt may be preferred for use in paediatric patients because of its neutral taste.
Familial neuromyelitis optica spectrum disorder in a pair of sisters

Cheo SW, Ong SAM, Low QJ, Tan YA, Chia YK

QJM, 2020 Oct 01;113(10):743-746.
PMID: 32240316 DOI: 10.1093/qjmed/hcaa107
Emulsion liquid membrane modeling for chromium removal from electroplating wastewater using TOMAC as a carrier

Othman N, Noah NFM, Sulaiman RNR, Jusoh N, Tan WT

Water Environ Res, 2021 Sep;93(9):1669-1679.
PMID: 33704848 DOI: 10.1002/wer.1551

Hexavalent chromium, emanating primarily from the electroplating industries, can be reduced to the less toxic trivalent variety by several methods, including emulsion liquid membrane (ELM). In this work, studies on the continuous removal of chromium from authentic electroplating wastewater by ELM are reported. The effects of treat ratio, external feed phase, and stripping agent concentration were examined. A mathematical boundary breakage model was used to study the extraction efficiency of chromium through the ELM process. The model representing the prediction of ELM extraction performance for chromium was validated through the comparison between the simulation and experimental results. The result showed the simulation model is found to be in good agreement with the experimental result. Almost 100% of 40 ppm chromium in the external feed phase was extracted within 3 to 5 min using 0.022 M TOMAC as extractant, 1.0 M acidic thiourea in the internal phase, and 1 to 5 of treat ratio. PRACTITIONER POINTS: Hexavalent chromium, emanating primarily from electroplating industries, can be reduced to the less toxic trivalent using ELM process. The developed method was tested for its applicability with predominant species of Cr2 O7 2- in real rinse electroplating wastewater. The extraction efficiency (%) of Cr (VI) was almost 100% for 40 ppm Cr in the external feed phase within 3 to 5 min. The result showed the simulation model is found to be in good agreement with the experimental result.

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