Displaying publications 61 - 80 of 101 in total

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  1. Chua KB, Lam SK, Goh KJ, Hooi PS, Ksiazek TG, Kamarulzaman A, et al.
    J Infect, 2001 Jan;42(1):40-3.
    PMID: 11243752
    To study the excretion of Nipah virus in the upper respiratory secretions and urine of infected patients in relation to other clinical features.
  2. Chan YP, Chua KB, Koh CL, Lim ME, Lam SK
    J Gen Virol, 2001 Sep;82(Pt 9):2151-5.
    PMID: 11514724
    We have completely sequenced the genomes of two Nipah virus (NiV) isolates, one from the throat secretion and the other from the cerebrospinal fluid (CSF) of the sole surviving encephalitic patient with positive CSF virus isolation in Malaysia. The two genomes have 18246 nucleotides each and differ by only 4 nucleotides. The NiV genome is 12 nucleotides longer than the Hendra virus (HeV) genome and both genomes have identical leader and trailer sequence lengths and hexamer-phasing positions for all their genes. Both NiV and HeV are also very closely related with respect to their genomic end sequences, gene start and stop signals, P gene-editing signals and deduced amino acid sequences of nucleocapsid protein, phosphoprotein, matrix protein, fusion protein, glycoprotein and RNA polymerase. The existing evidence demonstrates a clear need for the creation of a new genus within the subfamily Paramyxovirinae to accommodate the close similarities between NiV and HeV and their significant differences from other members of the subfamily.
  3. Ooi SL, Hooi PS, Chua BH, Lam SK, Chua KB
    Med J Malaysia, 2002 Mar;57(1):97-103.
    PMID: 14569725 MyJurnal
    A seroepidemiological study carried out on 800 stored serum samples collected between January 1999 to December 2000 derived from an urban population in Malaysia showed that the overall seropositive rate of human paravovirus B19 infection was 37.6%, with an overall geometric mean titre (GMT) of 18.3 IU. The seropositive rates of B19 among the male and female populations were 39.0% and 36.3% respectively. The seropositive rates among the racial groups were 37.2%, 38.2%, 38.1% and 29.4% respectively for the Malays, Chinese, Indians and other races. There was no statistical significant gender and racial differences in the B19 seropositive rates. When compared with the seroprevalence of B19 infection in other Asian countries, the seropositive rate of B19 in Malaysia was low in the younger age group and increased steadily with age. The unusual finding in this study was the presence of a high seropositive rate in those between six months to five years of age, especially in children in the one year old age group.
  4. Chua KB, Ngeow YF, Lim CT, Ng KB, Chye JK
    Med J Malaysia, 1999 Jun;54(2):242-6.
    PMID: 10972036
    A prospective study was carried out among pregnant women and their newborn babies in the University Hospital, Kuala Lumpur from January 1996 to June 1997. The maternal cervical colonization rates of Ureaplasma urealyticum (UU) and Mycoplasma hominis (MH) were found to be 57.5% and 15.8% respectively while the isolation rates from nasopharyngeal secretions of the newborns were 50.8% for UU and 6.6% for MH. The overall transmission rates were 88.4% for UU and 42.1% for MH. There was no significant difference in the transmission rates of either organism from mothers to their respective newborn babies by the maturity of pregnancy. In preterm babies, the nasopharyngeal isolation rates of UU and MH were not influenced by the babies' gestational age and birth weight nor by the maternal history of abortion or parity. However, there was a tendency for UU to persist in the nasopharyngeal secretion of preterm babies especially those of birth weight below 2 kg. None of the babies contaminated with mycoplasmas at birth developed respiratory symptoms during six to eight weeks of follow-up.
  5. Chan PW, Goh AY, Chua KB, Kharullah NS, Hooi PS
    J Paediatr Child Health, 1999 Jun;35(3):287-90.
    PMID: 10404452
    OBJECTIVE: To study the viral aetiology of lower respiratory tract infection (LRTI) in young Malaysian children.

    METHODOLOGY: A retrospective review was performed of LRTI patients aged less than 24 months who were admitted to the University Malaya Medical Centre between 1982 and 1997. Respiratory viruses in their nasopharyngeal secretion were identified by indirect immunofluorescence, viral culture, or both.

    RESULTS: A total of 5691 children were included in the study. The mean age was 8.6 +/- 6.6 months and the M:F ratio was 1.6:1. The most common diagnosis was pneumonia (52%) followed by bronchiolitis (45%) and croup (2%). Positive viral isolation rate was 22.0%. Respiratory syncytial virus (RSV) was the commonest virus isolated (84%), followed by parainfluenza virus (8%), influenza virus (6%) and adenovirus (2%). Patients with positive virus isolation were younger (7.8 +/- 6.2 vs 8.7 +/- 6.7 months, P = 0.0001) and were more likely to have bronchiolitis.

    CONCLUSION: Young Malaysian children admitted with LRTI had a 22% viral isolation rate and RSV was the commonest virus isolated.

  6. Hooi PS, Chua BH, Lee CSM, Lam SK, Chua KB
    Med J Malaysia, 2002 Mar;57(1):88-91.
    PMID: 14569723 MyJurnal
    The prevalence of HFMD as well as the causative agents was unknown in peninsular Malaysia prior to May 1997. From May 1997 to June 2001, 585 patients suspected to have enterovirus infections, with 467 patients clinically diagnosed as having HFMD, were investigated in the diagnostic virology unit of the University Malaya Medical Centre. Data from this study showed that HFMD is endemic in Malaysia with the occurrence of two outbreaks during the study period. In each outbreak, a number of viruses were isolated but enterovirus 71 was the main virus isolated in both outbreaks. Echovirus 7 (Eo7) was isolated from 5 patients with HFMD in the second outbreak, a clinical entity that has not been attributed to it previously. Children aged 4 years and below, particularly those between 1 and 2 years of age, were in the main group of patients affected by the illness. HFMD by itself and without neurological involvement was relatively benign and self-limiting. There was no significant difference in the virus isolation rate with respect to gender and ethnic groups. Virus isolation was attempted in a total of 764 clinical specimens consisting of 342 stool specimens, 285 oral secretions specimens and 137 vesicular fluid specimens. Oral specimens gave the highest virus isolation rate (33.3%) followed by vesicular specimens (27.0%). Stool specimens only yielded an isolation rate of 14.0%.
  7. Chua KB, Wang LF, Lam SK, Crameri G, Yu M, Wise T, et al.
    Virology, 2001 May 10;283(2):215-29.
    PMID: 11336547
    A search for the natural host of Nipah virus has led to the isolation of a previously unknown member of the family Paramyxoviridae. Tioman virus (TiV) was isolated from the urine of fruit bats (Pteropus hypomelanus) found on the island of the same name off the eastern coast of peninsular Malaysia. An electron microscopic study of TiV-infected cells revealed spherical and pleomorphic-enveloped viral particles (100--500 nm in size) with a single fringe of embedded peplomers. Virus morphogenesis occurred at the plasma membrane of infected cells and morphological features of negative-stained ribonucleoprotein complexes were compatible with that of viruses in the family Paramyxoviridae. Serological studies revealed no cross-reactivity with antibodies against a number of known Paramyxoviridae members except for the newly described Menangle virus (MenV), isolated in Australia in 1997. Failure of PCR amplification using MenV-specific primers suggested that this new virus is related to but different from MenV. For molecular characterization of the virus, a cDNA subtraction strategy was employed to isolate virus-specific cDNA from virus-infected cells. Complete gene sequences for the nucleocapsid protein (N) and phosphoprotein (P/V) have been determined and recombinant N and V proteins produced in baculovirus. The recombinant N and V proteins reacted with porcine anti-MenV sera in Western blot, confirming the serological cross-reactivity observed during initial virus characterization. The lack of a C protein-coding region in the P/V gene, the creation of P mRNA by insertion of 2-G residues, and the results of phylogenetic analyses all indicated that TiV is a novel member of the genus Rubulavirus.
  8. Chua KB, Lam SK, Hooi PS, Chua BH, Lim CT
    Med J Malaysia, 2000 Sep;55(3):299-303.
    PMID: 11200707
    A retrospective review of rubella serological results carried out in the Virus Diagnostic Unit, University Hospital Kuala Lumpur (UHKL) from January 1993 to September 1999 showed the presence of rubella infection annually which appeared to increase periodically every two to three years. There was no statistical significant difference in the rubella positive rate between male and female population aged 14 to 48 years. Congenital rubella infections (CRI) occurred in babies delivered in UHKL yearly from 1993 to 1998 with an average incidence rate of 48 per 100,000 deliveries. Peaks of rubella cases appeared to be followed by an increase in incidence of CRI cases 6 to 9 months later. The study showed that only 50.8% clinically diagnosed rubella was confirmed by laboratory finding. This study also showed an increase of rubella activity for the months of July, August and September 1999 and this may herald an increase of CRI cases in the coming millennium.
  9. Chua KB, Lam SK, AbuBakar S, Lim ST, Paranjothy M, Koh MT, et al.
    J Clin Virol, 2000 Aug;17(2):83-90.
    PMID: 10942088
    BACKGROUND: The clinical sign of uvulo-palatoglossal junctional (UPJ) ulcers was first noted in 1983 in a 5.5-month-old baby with exanthem subitum (ES). An earlier prospective clinical study showed that there was a strong association of UPJ ulcers and occurrence of ES with a positive predictive value of 95.3% and negative predictive value of 100%.

    OBJECTIVE: To determine the value of uvulo-palatoglossal junctional (UPJ) ulcers as an early clinical sign of exanthem subitum (ES) due to human herpesvirus 6 (HHV 6) infection.

    STUDY DESIGN: A case-control study of 20 febrile children with UPJ ulcers versus 26 febrile children without UPJ ulcers. These children were followed up for any development of ES and investigated for human herpesvirus 6 (HHV 6) as the causative agents of the febrile episodes.

    RESULTS: In this study, 20 out of 46 febrile children aged 3 months to 3 years with UPJ ulcers were virologically and/or serologically confirmed to be due to primary HHV 6 infection. The rest of the 26 children without ulcers did not have HHV 6 infection. Of the 20 children with UPJ ulcers, only 17 of the 19 children with adequate follow-up till subsidence of fever developed ES. None of the 26 children without UPJ ulcers developed ES.

    CONCLUSION: Statistically, there was a significant association of UPJ ulcers as an early sign of ES with a positive predictive value of 89.5% and negative predictive value of 100%. This finding also suggests that the presence of UPJ ulcers is a useful pathognomic clinical sign of symptomatic primary HHV 6 infection.

  10. Lum LC, Wong KT, Lam SK, Chua KB, Goh AY
    Lancet, 1998 Oct 24;352(9137):1391.
    PMID: 9802304
  11. AbuBakar S, Chee HY, Al-Kobaisi MF, Xiaoshan J, Chua KB, Lam SK
    Virus Res, 1999 May;61(1):1-9.
    PMID: 10426204
    Thirteen enterovirus 71 (EV71) isolates were obtained from both fatal and non-fatal infections of patients seen in Peninsula Malaysia and in Sarawak during an outbreak of hand, foot and mouth disease (HFMD) in Malaysia in 1997, with incidences of fatal brainstem encephalomyelitis. The isolates were identified using immunofluorescence staining, neutralization assays, and partial sequencing of the 5' untranslated regions (UTR). Assessment of the potential genetic relationships of the isolates using the partial 5'UTR sequences suggested clustering of the isolates into at least two main clusters. Isolates from Peninsula Malaysia were found in both clusters whereas Sarawak-derived isolates clustered only in cluster II. Isolates derived from fatal infections, however, occurred in both clusters and no distinctive nucleotide sequences could be attributed to the fatal isolates. Examination of the nucleotide sequences revealed at least 13 nucleotide positions in all the isolates which differ completely from the previously reported EV71 5'UTR sequences. In addition, at least 11 nucleotide position differences within the 5'UTR were noted which differentiated cluster I from cluster II. Predicted secondary RNA structures drawn using the nucleotide sequences also suggested differences between isolates from the two clusters. These findings suggest the presence of at least two potentially virulent EV71 co-circulating in Malaysia during the 1997 HFMD outbreak.
  12. Xu Y, Victorio CBL, Meng T, Jia Q, Tan YJ, Chua KB
    Virol Sin, 2019 Jun;34(3):262-269.
    PMID: 31016480 DOI: 10.1007/s12250-019-00116-1
    Our previous work has shown that Saffold virus (SAFV) induced several rodent and primate cell lines to undergo apoptosis (Xu et al. in Emerg Microb Infect 3:1-8, 2014), but the essential viral proteins of SAFV involved in apoptotic activity lack study. In this study, we individually transfected the viral proteins of SAFV into HEp-2 and Vero cells to assess their ability to induce apoptosis, and found that the 2B and 3C proteins are proapoptotic. Further investigation indicated the transmembrane domain of the 2B protein is essential for the apoptotic activity and tetramer formation of the 2B protein. Our research provides clues for the possible mechanisms of apoptosis induced by SAFV in different cell lines. It also opens up new directions to study viral proteins (the 2B, 3C protein), and sets the stage for future exploration of any possible link between SAFV, inclusive of its related uncultivable genotypes, and multiple sclerosis.
  13. Chua KB, Ngeow YF, Ng KB, Chye JK, Lim CT
    Singapore Med J, 1998 Jul;39(7):300-2.
    PMID: 9885690
    A prospective study was carried out at the University Hospital, Kuala Lumpur to determine the cervical carriage rate of Ureaplasma urealyticum and Mycoplasma hominis among healthy pregnant women at delivery and the incidence of nasopharyngeal colonisation among their infants.
  14. 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. 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. Warrener L, Slibinskas R, Chua KB, Nigatu W, Brown KE, Sasnauskas K, et al.
    Bull World Health Organ, 2011 Sep 01;89(9):675-82.
    PMID: 21897488 DOI: 10.2471/BLT.11.088427
    OBJECTIVE: To evaluate the performance of a newly developed point-of-care test (POCT) for the detection of measles-specific IgM antibodies in serum and oral fluid specimens and to assess if measles virus nucleic acid could be recovered from used POCT strips.

    METHODS: The POCT was used to test 170 serum specimens collected through measles surveillance or vaccination programmes in Ethiopia, Malaysia and the Russian Federation: 69 were positive for measles immunoglobulin M (IgM) antibodies, 74 were positive for rubella IgM antibodies and 7 were positive for both. Also tested were 282 oral fluid specimens from the measles, mumps and rubella (MMR) surveillance programme of the United Kingdom of Great Britain and Northern Ireland. The Microimmune measles IgM capture enzyme immunoassay was the gold standard for comparison. A panel of 24 oral fluids was used to investigate if measles virus haemagglutinin (H) and nucleocapsid (N) genes could be amplified by polymerase chain reaction directly from used POCT strips.

    FINDINGS: With serum POCT showed a sensitivity and specificity of 90.8% (69/76) and 93.6% (88/94), respectively; with oral fluids, sensitivity and specificity were 90.0% (63/70) and 96.2% (200/208), respectively. Both H and N genes were reliably detected in POCT strips and the N genes could be sequenced for genotyping. Measles virus genes could be recovered from POCT strips after storage for 5 weeks at 20-25 °C.

    CONCLUSION: The POCT has the sensitivity and specificity required of a field-based test for measles diagnosis. However, its role in global measles control programmes requires further evaluation.

  17. Moi ML, Lim CK, Chua KB, Takasaki T, Kurane I
    PLoS Negl Trop Dis, 2012;6(2):e1536.
    PMID: 22389741 DOI: 10.1371/journal.pntd.0001536
    Progress in dengue vaccine development has been hampered by limited understanding of protective immunity against dengue virus infection. Conventional neutralizing antibody titration assays that use FcγR-negative cells do not consider possible infection-enhancement activity. We reasoned that as FcγR-expressing cells are the major target cells of dengue virus, neutralizing antibody titration assays using FcγR-expressing cells that determine the sum of neutralizing and infection-enhancing activity, may better reflect the biological properties of antibodies in vivo.
  18. Luena Victorio CB, Chua IL, Xu Y, Ng Q, Chua BH, Chow VTK, et al.
    Malays J Pathol, 2024 Apr;46(1):51-62.
    PMID: 38682844
    Small animal models play an important role in investigating and revealing the molecular determinants and mechanisms underlying neuro-virulence of enterovirus A71 (EV-A71). In our previous study, we successfully developed two mouse cell-line replication competent EV-A71 strains (EV71:TLLm and EV71:TLLmv) which were capable of inducing neuro-invasion in BALB/c mice. The more virulent EV71:TLLmv exhibited ability to induce acute encephalomyelitis accompanied by neurogenic pulmonary oedema. EV71:TLLcho virus strain was generated from EV71:TLLm by a series of passages in CHO-K1 cells. EV71:TLLcho demonstrated a broader range of infectivity across various mammalian cell lines and exhibited complete cytopathic effects (CPE) within 48 hours post-inoculation in comparison to EV71:TLLm or EV71:TLLmv. EV71:TLLcho consistently yielded higher levels of viral replication at all time points examined. In comparison to EV71:TLLm, EV71:TLLcho consistently induced more severe disease and increased mortality in one-week old BALB/c mice. However, unlike mice challenged with EV71:TLLmv, none of the mice challenged with EV71:TLLcho progressed to severe acute encephalomyelitis and developed neurogenic pulmonary oedema.
  19. Yaiw KC, Ong KC, Chua KB, Bingham J, Wang L, Shamala D, et al.
    J Virol Methods, 2007 Aug;143(2):140-6.
    PMID: 17442409
    Tioman virus is a newly described bat-urine derived paramyxovirus isolated in Tioman Island, Malaysia in 2001. Hitherto, neither human nor animal infection by this virus has been reported. Nonetheless, its close relationship to another paramyxovirus, the Menangle virus which had caused diseases in humans and pigs [Philbey, A.W., Kirkland, P.D., Ross, A.D., Davis, R.J., Gleeson, A.B., Love, R.J., Daniels, P.W., Gould, A.R., Hyatt, A.D., 1998. An apparently new virus (family Paramyxoviridae) infectious for pigs, humans, and fruit bats. Emerg. Infect. Dis. 4, 269-271], raises the possibility that it may be potentially pathogenic. In this study, mice were experimentally infected with Tioman virus by intraperitoneal and intracerebral routes, and the cellular targets and topographical distribution of viral genome and antigens were examined using in situ hybridization and immunohistochemistry, respectively. The possible association between viral infection and apoptosis was also investigated using the TUNEL assay and immunohistochemistry to FasL, Caspase-3, Caspase-8, Caspase-9 and bcl-2. The results showed that Tioman virus inoculated intracerebrally was neurotropic causing plaque-like necrotic areas, and appeared to preferentially replicate in the neocortex and limbic system. Viral infection of inflammatory cells was also demonstrated. TUNEL and Caspase-3 positivity was found in inflammatory cells but not in neurons, while FasL, Caspase-8 and Caspase-9 were consistently negative. This suggests that neuronal infection was associated with necrosis rather than apoptosis. Moreover, the data suggest that there may be an association between viral infection and apoptosis in inflammatory cells, and that it could, at least in part, involve Caspase-independent pathways. Bcl-2 was expressed in some neurons and inflammatory cells indicating its possible role in anti-apoptosis. There was no evidence of central nervous system infection via the intraperitoneal route.
  20. 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.
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