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  1. Fulltext Monoclonal antibody-escape variant of dengue virus serotype 1: Genetic composition and envelope protein expression
    Chem YK, Chua KB, Malik Y, Voon K
    Trop Biomed, 2015 Jun;32(2):344-51.
    PMID: 26691263 MyJurnal
    Monoclonal antibody-escape variant of dengue virus type 1 (MabEV DEN-1) was discovered and isolated in an outbreak of dengue in Klang Valley, Malaysia from December 2004 to March 2005. This study was done to investigate whether DEN152 (an isolate of MabEV DEN-1) is a product of recombination event or not. In addition, the non-synonymous mutations that correlate with the monoclonal antibody-escape variant were determined in this study. The genomes of DEN152 and two new DEN-1 isolates, DENB04 and DENK154 were completely sequenced, aligned, and compared. Phylogenetic tree was plotted and the recombination event on DEN152 was investigated. DEN152 is sub-grouped under genotype I and is closely related genetically to a DEN-1 isolated in Japan in 2004. DEN152 is not a recombinant product of any parental strains. Four amino acid substitutions were unique only to DEN 152. These amino acid substitutions were (Ser)[326](Leu), (Ser)[340](Leu) at the deduced E protein, (Ile)[250](Thr) at NS1 protein, and (Thr)[41](Ser) at NS5 protein. Thus, DEN152 is an isolate of the emerging monoclonal antibody-escape variant DEN-1 that escaped diagnostic laboratory detection.
  2. Fulltext Chikungunya virus of Central/East African genotype detected in Malaysia
    Soon YY, Junaidi I, Kumarasamy V, Chem YK, Juliana R, Chua KB
    Med J Malaysia, 2007 Aug;62(3):214-7.
    PMID: 18246910 MyJurnal
    Since its isolation in Tanzania in 1953, chikungunya virus has caused periodic outbreaks in both tropical Africa and Asia. In the last decade, the virus has shown not only increased activity but has expanded its geographical locations, thus classical delineation of various genotypes of chikungunya virus to specific geographic locales no longer holds true. Rapid mass movement of people and the constant presence of the right vectors in this region could have contributed to the change in virus ecology. This paper documents the first detection of chikungunya virus of Central/East genotype in Malaysia from a patient who was most likely infected with the virus during her visit to India. Without good Aedes vector measures, only time will tell whether this genotype rather than the existing endemic genotype will subsequently cause the next chikungunya outbreak in Malaysia.
  3. Fulltext Re-emergence of Chikungunya virus in Malaysia
    Kumarasamy V, Prathapa S, Zuridah H, Chem YK, Norizah I, Chua KB
    Med J Malaysia, 2006 Jun;61(2):221-5.
    PMID: 16898316 MyJurnal
    An outbreak of Chikugunya (CHIK) fever occurred among the fishing community in Bagan Pancor, Perak. The outbreak was laboratory confirmed within 48 hours after the receipt of the specimens. Fifty-three patients' serum samples were submitted for laboratory investigation and 47 (88.7%) were confirmed to be positive for CHIK infection by RT-PCR, and/or virus isolation, and/or in-house immunoflourescent test. RT-PCR and virus isolation were the tests of choice for patients with illness of four days or less and detection of CHIK specific IgM for those with more than four days of fever. The nucleic acid sequence based on the 354- and 294-bp of the nsP1 and E1 genes of the CHIK virus detected from pools of adults Aedes aegypti mosquitoes were identical to those CHIKV virus isolated from humans in the same locality. Phylogenetic analysis of the CHIK virus based on the 257 nts partial E1 gene indicates that Bagan Panchor's strain was closely related to the first CHIK virus isolated during the outbreak in Klang in 1998.
  4. Fulltext A comparative evaluation of dengue diagnostic tests based on single-acute serum samples for laboratory confirmation of acute dengue
    Chua KB, Mustafa B, Abdul Wahab AH, Chem YK, Khairul AH, Kumarasamy V, et al.
    Malays J Pathol, 2011 Jun;33(1):13-20.
    PMID: 21874746
    A prospective study was carried out to evaluate the sensitivity of dengue NS1 antigen-capture ELISA in comparison with dengue virus isolation, conventional RT-PCR and real-time RT-PCR for laboratory confirmation of acute dengue based on single-acute serum samples. Four primary healthcare centres were involved to recruit patients with clinical diagnosis of dengue illness. Patient's demographic, epidemiological and clinical information were collected on a standardized data entry form and 5 ml of venous blood was collected upon consent. In the laboratory, six types of laboratory tests were performed on each of the collected acute serum sample. Of the 558 acute serum samples collected from 558 patients with clinical diagnosis of dengue from mid-August 2006 to March 2009, 174 serum samples were tested positive by the dengue NS1 antigen-capture ELISA, 77 by virus isolation, 92 by RT-PCR and 112 by real-time RT-PCR. A total of 190 serum samples were tested positive by either one or a combination of the four methods whereas, only 59 serum samples were tested positive by all four methods. Thus, based on single-acute serum samples, 190 of the 558 patients (34.1%) were laboratory-confirmed acute dengue. The overall test sensitivity was 91.6%, 40.5%, 48.4% and 58.9% for dengue NS1 antigen-capture ELISA, virus isolation, conventional RT-PCR and real-time RT-PCR respectively. Statistically, dengue NS1 antigen-capture ELISA was the most sensitive and virus isolation was the least sensitive test for the laboratory confirmation of acute dengue based on single-acute serum specimens. Real-time RT-PCR was significantly more sensitive than the conventional RT-PCR.
  5. Fulltext Epidemiological and clinical features of dengue versus other acute febrile illnesses amongst patients seen at government polyclinics
    Mustafa B, Hani AW, Chem YK, Mariam M, Khairul AH, Abdul Rasid K, et al.
    Med J Malaysia, 2010 Dec;65(4):291-6.
    PMID: 21901948
    Classical dengue fever is characterized by the clinical features of fever, headache, severe myalgia and occasionally rash, which can also be caused by a number of other viral and bacterial infections. Five hundred and fifty eight patients who fulfilled the criteria of clinical diagnosis of acute dengue from 4 government outpatient polyclinics were recruited in this prospective field study. Of the 558 patients, 190 patients were categorized as acute dengue fever, 86 as recent dengue and 282 as non-dengue febrile illnesses based on the results of a number of laboratory tests. Epidemiological features of febrile patients showed that the mean age of patients in the dengue fever group was significantly younger in comparison with patients in the non-dengue group. There was no significant difference between the two groups with respect to gender but there was significant ethnic difference with foreign workers representing a higher proportion in the dengue fever group. Patients with acute dengue fever were more likely to have patient-reported rash and a history of dengue in family or neighbourhood but less likely to have respiratory symptoms, sore-throat and jaundice in comparison to patients with non-dengue febrile illnesses. As with patients with dengue fever, patients in the recent dengue group were more likely to have history of patient-reported rash and a history of dengue contact and less likely to have respiratory symptoms in comparison to patients with non-dengue febrile illnesses. In contrast to patients with dengue fever, patients in the recent dengue group were more likely to have abdominal pain and jaundice in comparison to non-dengue febrile patients. The finding strongly suggests that a proportion of patients in the recent dengue group may actually represent a subset of patients with acute dengue fever at the late stage of illness.
    Study site: Klinik Kesihatan Seksyen 7, Shah Alam; Klinik Kesihatan Kelana Jaya, Petaling Jaya; Klinik Kesihatan Sg. Buloh; Klinik Kesihatan Jinjang, Selangor, Kuala Lumpur, Malaysia
  6. Fulltext A fatal case of chikungunya virus infection with liver involvement
    Chua HH, Abdul Rashid K, Law WC, Hamizah A, Chem YK, Khairul AH, et al.
    Med J Malaysia, 2010 Mar;65(1):83-4.
    PMID: 21265260 MyJurnal
    Recovery from chikungunya is previously considered universal and mortality due to the virus is rare and unusual. Findings from recent chikungunya outbreaks occurred in Reunion Island and India have since challenged the conventional view on the benign nature of the illness. Malaysia has experienced at least of 4 outbreaks of chikungunya since 1998. In the present on-going large outbreak due to chikungunya virus of Central/East African genotype, a previous healthy sixty six years gentleman without co-morbidity was noted to have severe systemic infection by the virus and involvement of his liver. He subsequently passed away due to cardiovascular collapse after 5 days of illness.
  7. Fulltext Broad reactive monoclonal antibodies for rapid identification of enteroviruses show cross-reactivity with chikungunya virus infected cells
    Khairul AH, Chem YK, Keniscope C, Rosli J, Hassan S, Mat J, et al.
    Malays J Pathol, 2010 Jun;32(1):49-52.
    PMID: 20614726 MyJurnal
    In the past decade, enterovirus 71 (EV71) and chikungunya (CHIK) virus have re-emerged periodically causing serious public health problems in Malaysia, since their first emergence in 1997 and 1998 respectively. This study demonstrates that CHIK virus causes similar patterns of cytopathic effect in cultured Vero cells as some enteroviruses. They also show positive cross-reaction on direct immunofluorescence staining using monoclonal antibodies meant for typing enteroviruses. Without adequate clinical and epidemiological information for correlation, CHIK virus isolated from patients with acute febrile rash can be wrongly reported as untypeable enterovirus due to its cross-reactivity with commercial pan-enterovirus monoclonal antibodies. This is due to the diagnostic laboratory being unaware of such cross-reactions as it has not been reported previously. Final identification of the virus could be determined with specific antibodies or molecular typing using specific oligonucleotide primers for the CHIK virus.
  8. Fulltext Molecular epidemiology of chikungunya virus in Malaysia since its first emergence in 1998
    Chem YK, Zainah S, Berendam SJ, Rogayah TA, Khairul AH, Chua KB
    Med J Malaysia, 2010 Mar;65(1):31-5.
    PMID: 21265245 MyJurnal
    Malaysia experienced the first outbreak of chikungunya (CHIK) in Klang in late 1998 due to CHIK virus of Asian genotype. The CHIK virus of Asian genotype reemerged causing outbreak in Bangan Panchor, Perak in March 2006. CHIK virus of Central/East African genotype was first detected from a patient who returned from India in August 2006. In December 2006, CHIK virus of Central/East African genotype was re-introduced into Malaysia from India and caused an outbreak in Kinta district, Perak but was successfully controlled following an early detection and institution of intensive vector control measures. In late April 2008, CHIK virus of Central/East African genotype was laboratory confirmed as the cause of CHIK outbreak in Johore which spread to other parts of Malaysia by August 2008. Phylogenetic analysis based on the 254-bp fragment of the virus envelope protein gene as the genetic marker showed that three different strains of CHIK virus of Central/East African genotype were introduced into Malaysia on three separate occasions from 2006 to 2008. The strain that was introduced into Johor state was responsible for its subsequent spread to other parts of Malaysia, inclusive of Sarawak.
  9. Fulltext Outbreak of chikungunya due to virus of Central/East African genotype in Malaysia
    Noridah O, Paranthaman V, Nayar SK, Masliza M, Ranjit K, Norizah I, et al.
    Med J Malaysia, 2007 Oct;62(4):323-8.
    PMID: 18551938 MyJurnal
    Chikungunya is an acute febrile illness caused by an alphavirus which is transmitted by infective Aedes mosquitoes. Two previous outbreaks of chikungunya in Malaysia were due to chikungunya virus of Asian genotype. The present outbreak involved two adjoining areas in the suburb of Ipoh city within the Kinta district of Perak, a state in the northern part of Peninsular Malaysia. Thirty seven residents in the main outbreak area and two patients in the secondary area were laboratory confirmed to be infected with the virus. The index case was a 44-year Indian man who visited Paramakudi, Tamil Naidu, India on 21st November 2006 and returned home on 30th of November 2006, and subsequently developed high fever and joint pain on the 3rd of December 2006. A number of chikungunya virus isolates were isolated from both patients and Aedes albopictus mosquitoes in the affected areas. Molecular study showed that the chikungunya virus causing the Kinta outbreak was of the Central/East African genotype which occurred for the first time in Malaysia.
  10. Fulltext Co-infection of dengue virus and chikungunya virus in two patients with acute febrile illness
    Nayar SK, Noridah O, Paranthaman V, Ranjit K, Norizah I, Chem YK, et al.
    Med J Malaysia, 2007 Oct;62(4):335-6.
    PMID: 18551940 MyJurnal
    During an outbreak of chikungunya in a dengue hyperendemic area within the Kinta district of Perak, two patients with acute febrile illness were laboratory confirmed to have co-infection of both dengue and chikungunya viruses in their blood. The concomitant presence of two types of viruses transmitted by the same vector in a susceptible population contributed to the resultant event. A good understanding of virus vector ecology in association with population dynamics and wider application of improved laboratory techniques by using different cell-lines suited for optimal replication of each type of virus and the correct utilization of powerful molecular techniques will enhance accurate diagnosis of these infectious diseases.
  11. Genetic diversity of enterovirus 71 isolated from cases of hand, foot and mouth disease in the 1997, 2000 and 2005 outbreaks, Peninsular Malaysia
    Chua KB, Chua BH, Lee CS, Chem YK, Ismail N, Kiyu A, et al.
    Malays J Pathol, 2007 Dec;29(2):69-78.
    PMID: 19108398
    All known field isolates of enterovirus 71 (EV71) can be divided into three distinct genogroups (A, B, C) and 10 subgenogroups (A, B1-5, C1-4) based on VP1 gene sequences. We examined VP1 gene sequences of 10, 12 and 11 EV71 strains isolated in peninsular Malaysia during the outbreaks of hand, foot and mouth disease in 1997, 2000 and 2005 respectively. Four EV71 strains isolated in the hand, foot and mouth disease outbreak of 2006 in Sarawak (Malaysian Borneo) were included to describe their genetic relationship. Four subgenogroups (C1, C2, B3 and B4) of EV71 co-circulated and caused the outbreak of hand, foot and mouth disease in peninsular Malaysia in 1997. Two subgenogroups (C1 and B4) were noted to cause the outbreak in 2000. In the 2005 outbreak, besides EV71 strains of subgenogroup C1, EV71 strains belonged to subgenogroup B5 were isolated but formed a cluster which was distinct from EV71 strains of the subgenogroup B5 isolated in 2003. The four EV71 strains isolated from clinical specimens of patients with hand, foot and mouth disease in the Sarawak outbreak in early 2006 also belonged to subgenogroup B5. Phylogenetic analysis of the VP1 gene sequences showed that the four Sarawak EV71 isolates belonged to the same cluster as the EV71 strains that were isolated in peninsular Malaysia as early as May 2005. The data suggested that the EV71 strains causing the outbreak in Sarawak could have originated from peninsular Malaysia.
  12. Fulltext Acute dengue in a neonate secondary to perinatal transmission
    Chin PS, Khoo AP, Asmah Hani AW, Chem YK, Norizah I, Chua KB
    Med J Malaysia, 2008 Aug;63(3):265-6.
    PMID: 19248708 MyJurnal
    We report a newborn baby girl with acute dengue due to vertical transmission. A 31 year old factory worker of 38+ week gestation, gravida 5 para 3+1, developed acute dengue fever two days prior to delivery. She delivered a normal term baby girl by spontaneous vaginal delivery and recovered uneventfully without peripartum haemorrhage despite the presence of thrombocytopenia. The baby girl developed low grade fever on day four of post-natal life and except for the transient thrombocytopenia, also recovered uneventfully following three days of mild illness. The clinical diagnosis of acute dengue virus infection was confirmed by laboratory tests.
  13. Fulltext 2013 dengue outbreaks in Singapore and Malaysia caused by different viral strains
    Ng LC, Chem YK, Koo C, Mudin RNB, Amin FM, Lee KS, et al.
    Am J Trop Med Hyg, 2015 Jun;92(6):1150-1155.
    PMID: 25846296 DOI: 10.4269/ajtmh.14-0588
    Characterization of 14,079 circulating dengue viruses in a cross-border surveillance program, UNITEDengue, revealed that the 2013 outbreaks in Singapore and Malaysia were associated with replacement of predominant serotype. While the predominant virus in Singapore switched from DENV2 to DENV1, DENV2 became predominant in neighboring Malaysia. Dominance of DENV2 was most evident on the southern states where higher fatality rates were observed.
  14. Fulltext Isolation of monoclonal antibodies-escape variant of dengue virus serotype 1
    Chua SK, Selvanesan S, Sivalingam B, Chem YK, Norizah I, Zuridah H, et al.
    Singapore Med J, 2006 Nov;47(11):940-6.
    PMID: 17075660
    During an outbreak from December 2004 to March 2005, 138 isolates of dengue virus were prospectively obtained from acute-phase serum samples of 1,067 patients with the provisional clinical diagnosis of acute dengue illness admitted to the adult wards of Hospital Tengku Ampuan Rahimah, Klang, Malaysia. Of the 138 dengue virus isolates, 87, 11, 24 and 3 were typed as dengue serotypes 1, 2, 3 and 4, respectively, by a commercial dengue virus typing kit using monoclonal antibodies (Mab). 13 dengue virus isolates could not be assigned to any specific serotype by serotyping Mab and molecular typing using dengue-type specific molecular typing primer pairs. We report the associated clinical features and limited molecular genetics of this Mab-escape dengue virus variant.
  15. Fulltext Evaluating the sensitivity of a commercial dengue NS1 antigen-capture ELISA for early diagnosis of acute dengue virus infection
    Kumarasamy V, Chua SK, Hassan Z, Wahab AH, Chem YK, Mohamad M, et al.
    Singapore Med J, 2007 Jul;48(7):669-73.
    PMID: 17609831
    INTRODUCTION: The aim of this report is to establish an accurate diagnosis of acute dengue virus infection early, in order to provide timely information for the management of patients and early public health control of dengue outbreak.
    METHODS: 224 serum samples from patients with a clinical diagnosis of acute dengue infection, which were subsequently confirmed by laboratory tests, were used to evaluate the performance of a commercially-available dengue NS1 antigen-capture ELISA kit.
    RESULTS: The dengue NS1 antigen-capture ELISA gave an overall sensitivity rate of 93.3 percent (209/224). The sensitivity rate was significantly higher in acute primary dengue (97.4 percent) than in acute secondary dengue (68.8 percent). In comparison, the virus isolation gave an overall positive isolation rate of 64.7 percent, with a positive rate of 70.8 percent and 28.1 percent, for acute primary dengue and acute secondary dengue, respectively. Molecular detection of dengue RNA by RT-PCR gave an overall positive detection rate of 63.4 percent, with a positive rate of 62.5 percent and 68.8 percent, for acute primary dengue and acute secondary dengue, respectively. Of the 224 acute serum samples from patients with laboratory-confirmed acute dengue infection, dengue IgM was detected in 88 specimens, comprising 68 acute primary dengue specimens and 20 acute secondary dengue specimens. NS1 antigen-capture ELISA kit gave an overall sensitivity rate of 88.6 percent in the presence of anti-dengue IgM and 96.3 percent in the absence of anti-dengue IgM.
    CONCLUSION: Of the 224 acute serum samples, the sample ages of 166 acute serum samples are known. The positive detection rate of dengue NS1 antigen-capture ELISA, on the whole, was higher than the other three established diagnostic test methods for laboratory diagnosis of acute dengue infection.
  16. Fulltext Evaluation of a commercial dengue NS1 antigen-capture ELISA for laboratory diagnosis of acute dengue virus infection
    Kumarasamy V, Wahab AH, Chua SK, Hassan Z, Chem YK, Mohamad M, et al.
    J Virol Methods, 2007 Mar;140(1-2):75-9.
    PMID: 17140671
    A commercial dengue NS1 antigen-capture ELISA was evaluated to demonstrate its potential application for early laboratory diagnosis of acute dengue virus infection. Dengue virus NS1 antigen was detected in 199 of 213 acute serum samples from patients with laboratory confirmation of acute dengue virus infection but none of the 354 healthy blood donors' serum specimens. The dengue NS1 antigen-capture ELISA gave an overall sensitivity of 93.4% (199/213) and a specificity of 100% (354/354). The sensitivity was significantly higher in acute primary dengue (97.3%) than in acute secondary dengue (70.0%). The positive predictive value of the dengue NS1 antigen-capture ELISA was 100% and negative predictive value was 97.3%. Comparatively, virus isolation gave an overall positive isolation rate of 68.1% with a positive isolation rate of 73.9 and 31.0% for acute primary dengue and acute secondary dengue, respectively. Molecular detection of dengue RNA by RT-PCR gave an overall positive detection rate of 66.7% with a detection rate of 65.2 and 75.9% for acute primary dengue and acute secondary dengue, respectively. The results indicate that the commercial dengue NS1 antigen-capture ELISA may be superior to virus isolation and RT-PCR for the laboratory diagnosis of acute dengue infection based on a single serum sample.
  17. Fulltext A measles IgM rapid diagnostic test to address challenges with national measles surveillance and response in Malaysia
    Senin A, Noordin NM, Sani JAM, Mahat D, Donadel M, Scobie HM, et al.
    PLoS One, 2024;19(3):e0298730.
    PMID: 38483868 DOI: 10.1371/journal.pone.0298730
    INTRODUCTION: A lateral flow rapid diagnostic test (RDT) enables detection of measles specific immunoglobulin M (IgM) antibody in serum, capillary blood, and oral fluid with accuracy consistent with enzyme immunoassay (EIA). The objectives of the study were: 1) to assess measles RDT inter-reader agreement between two clinic staff; 2) to assess the sensitivity and specificity of the measles RDT relative to standard surveillance testing in a low transmission setting; 3) to evaluate the knowledge, attitudes, and practices of staff in clinics using the RDT; and 4) to assess the impact of RDT testing on the measles public health response in Malaysia.

    MATERIALS AND METHODS: The clinic-based prospective evaluation included all suspected measles cases captured by routine measles surveillance at 34 purposely selected clinics in 15 health districts in Malaysia between September 2019 and June 2020, following day-long regional trainings on RDT use. Following informed consent, four specimens were collected from each suspected case, including those routinely collected for standard surveillance [serum for EIA and throat swabs for quantitative reverse transcriptase polymerase chain reaction (RT-qPCR)] together with capillary blood and oral fluid tested with RDTs during the study. RDT impact was evaluated by comparing the rapidity of measles public health response between the pre-RDT implementation (December 2018 to August 2019) and RDT implementation periods (September 2019 to June 2020). To assess knowledge, attitudes, and practices of RDT use, staff involved in the public health management of measles at the selected sites were surveyed.

    RESULTS: Among the 436 suspect cases, agreement of direct visual readings of measles RDT devices between two health clinic staff was 99% for capillary blood (k = 0.94) and 97% for oral fluid (k = 0.90) specimens. Of the total, 45 (10%) were positive by measles IgM EIA (n = 44, including five also positive by RT-qPCR) or RT-qPCR only (n = 1), and 38 were positive by RDT (using either capillary blood or oral fluid). Using measles IgM EIA or RT-qPCR as reference, RDT sensitivity using capillary blood was 43% (95% CI: 30%-58%) and specificity was 98% (95% CI: 96%-99%); using oral fluid, sensitivity (26%, 95% CI: 15%-40%) and specificity (97%, 95% CI: 94%-98%) were lower. Nine months after training, RDT knowledge was high among staff involved with the public health management of measles (average quiz score of 80%) and was highest among those who received formal training (88%), followed by those trained during supervisory visits (83%). During the RDT implementation period, the number of days from case confirmation until initiation of public response decreased by about 5 days.

    CONCLUSION: The measles IgM RDT shows >95% inter-reader agreement, high retention of RDT knowledge, and a more rapid public health response. However, despite ≥95% RDT specificity using capillary blood or oral fluid, RDT sensitivity was <45%. Higher-powered studies using highly specific IgM assays and systematic RT-qPCR for case confirmation are needed to establish the role of RDT in measles elimination settings.

  18. Linkage disequilibrium suggests genomic stability in Omicron clades of SARS-CoV-2 from the ASEAN countries
    Yusof NBM, Khor ZS, Bakar RSBA, Zaman KHBK, Chem YK, Fatini NA, et al.
    J Travel Med, 2023 Sep 05;30(5).
    PMID: 36795049 DOI: 10.1093/jtm/taad020
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