Biomedical subjects
Publications and source records attributed to A E Ling.
We describe an atypical presentation of severe acute respiratory syndrome (SARS) in a geriatric patient with multiple coexisting conditions. Interpretation of radiographic changes was confounded by cardiac failure, with resolution of fever causing delayed diagnosis and a cluster of cases. SARS should be considered even if a contact history is unavailable, during an ongoing outbreak.
An isolate from a patient in the recent severe acute respiratory syndrome (SARS) outbreak in Singapore was used to infect Vero E6 cells. This study concentrated on the first 30 min of infection. It was discovered that the SARS coronavirus attached, entered, and uncoated the nucleocapsids, all within a 30-min period. At 5 min after infection, several virus particles lined the Vero cell plasma membrane. Virus particles were at various stages of fusion at the cell surface, since entry was not a synchronised process. After entry (10 and 15 min), spherical core particles moved into the cytoplasm within large vacuoles. Quite surprising at such early stages of infection (20 min), a virus-induced change in the infected cells was evident. The induction of myelin-like membrane whorls was obvious within the same vacuoles as the core particles. The significance of this virus-induced change is unknown at this stage. By 25-30 min postinfection (p.i.), the spherical core particles appeared to be disassociating and, in their place, doughnut-shaped electron-dense structures were observed. These could be the virus genomes together with the helical nucleocapsids. They were no longer in large vacuoles but packaged into smaller vacuoles in the cytoplasm, and occasionally in small groups.
The Nipah virus is a newly identified paramyxovirus responsible for an outbreak of fatal encephalitis in Malaysia and Singapore. This paper reports the follow up clinical and magnetic resonance imaging findings in 22 affected subjects. Of 13 patients with encephalitis, one died, one was lost to follow up, and seven recovered. Among the four remaining patients, one had residual sixth nerve palsy, another suffered from severe clinical depression, and a third patient had evidence of retinal artery occlusion. One patient with delayed onset Horner syndrome had a single lesion in the cervical spinal cord. The brain magnetic resonance findings were stable or improved in nine patients over 18 months of follow up. Among a second group of nine asymptomatic seropositive abattoir workers, magnetic resonance examination in seven subjects revealed discrete small lesions in the brain; similar to those detected in encephalitis patients. These findings suggest that in addition to encephalitis, the newly discovered Nipah virus affects the spinal cord and the retina. Late clinical and radiological findings can occur in Nipah virus infections as with other paramyxoviruses.
BACKGROUND: We experienced a hand, foot and mouth disease (HFMD) outbreak in late year 2000 in Singapore. Between 14 September 2000 and 14 November 2000, a total of 3526 cases of HFMD were notified. There were 652 patients clinically suspected to have HFMD, who were seen at the Children's Emergency department of KK Women's and Children's Hospital of Singapore. OBJECTIVE OF THE STUDY: To study the clinical profile and virologic isolates of children admitted with HFMD during the outbreak. STUDY DESIGN: A prospective observational study. METHODS: Analysis of clinical features and virologic studies of 129 selected cases of HFMD and herpangina. RESULTS: The median age was 25 months with a range of between 4 months and 11 years. The majority were less than 5 years old (87%). The male-to-female ratio was 1.3:1. The median numbers of day of illness to presentation to the hospital was 3 days. Poor feeding and loss of appetite accounted for 76.7% of the admissions. Symptoms of vomiting were present in 37.2% of the cases. Oral ulcers were found in 96.1%, rashes over hands in 87.6%, over feet in 86.8% and over buttocks in 54.3%. Only 4.7% exhibited no rashes other than oral ulcers and were labelled as herpangina. The median duration of fever was 3 days, ranging from 2 to 7 days. An intravenous drip was required in 68.2% due to poor feeding. Viral cultures were sent in 89.1% of patients of whom 61.7% of patients were positive for viruses. Of the positive cultures, types of viruses isolated were EV71 (enterovirus 71) in 59/71 (83%), Coxsackievirus (A16, A24, A2 B3, B4) in 6/71 (8.4%), EV Untypable in 4/71 (5.6%) and mixed [EV71, echo25, cytomegalovirus (CMV)] in 2/71 (2.8%). EV71 was isolated mostly from stool samples followed by vesicle fluid culture and throat swabs. Two siblings aged 14 months and 2.5 years died during this period at day 5 of illness, their post-mortem examinations showed interstitial pneumonitis of the lungs. EV71 was isolated from the brain, heart, tonsils, intestines, throat and rectal swabs. A raised total white cell count of 14,000/L versus 12,000/L was significantly associated with complicated HFMD (P = 0.04). There was no difference in clinical characteristics of EV71 versus non-EV71 infections. Other viral illnesses, e.g. measles and CMV, may be mistaken for HFMD in the outbreak setting. CONCLUSIONS: HFMD tends to occur in younger children less than 5 years old due to low herd immunity. Poor feeding due to mouth ulcers accounts for admission to hospital requiring intravenous drip. EV71 accounted for the majority (75%) of the positive isolations, followed by coxsackievirus and untypable EV, mixed infection of echovirus or CMV. The yield of virus isolation was highest from stool, followed by vesicles and throat swabs. There is no difference in clinical characteristics of EV71 and non-EV71 virus infections. Enterovirus can cause mild symptoms to fatal death. Two infants died of interstitial pneumonitis and encephalitis.
AIM: An epidemic of hand, foot and mouth disease (HFMD) occurred in Singapore between September and November 2000. During the epidemic, there were four HFMD-related deaths and after the epidemic, another three HFMD-related deaths. This study sought to determine the risk factors predictive of death from HFMD disease. METHODS: The risk factors for fatal HFMD were determined by comparing clinical and laboratory findings between fatal cases (n = 7) and non-fatal controls (n = 131) admitted between September 2000 and April 2001. Enterovirus 71 positive fatal cases (n = 4) and non-fatal controls (n = 63) were also compared. RESULTS: In total, 138 HFMD cases with a mean age of 32 mo were studied. The majority of fatal cases died from interstitial pneumonitis, of whom three also had brainstem encephalitis. Of the 131 non-fatal cases, 3 had concomitant infections (respiratory syncytial virus bronchiolitis, right-sided pneumonia, Haemophilus influenzae type b meningitis), 2 had aseptic meningitis, and 1 each had transient drowsiness, intravenous immunoglobulin-related complications and transverse myelitis. By multivariate logistic regression analysis, atypical physical findings (p = 0.0006), raised total white cell count (p = 0.0128), vomiting (p = 0.0116) and absence of mouth ulcers (p = 0.043) were predictive of a fatal course. Although previous epidemics have described neurogenic pulmonary oedema as the main cause of death, the fatal cases in this study died mainly from interstitial pneumonitis alone or with myocarditis or encephalitis. CONCLUSION: Although HFMD is generally a benign disease, risk factors such as vomiting, absence of mouth ulcers, atypical presentation and raised total white cell count should alert the physician of a fatal course of illness.
Following the Nipah virus (NV) outbreak in March 1999 in Singapore, a serological survey was undertaken to screen individuals potentially exposed to NV. Blood samples were tested for NV IgM, IgG and neutralizing antibodies. Twenty-two (1.5%) of 1469 people tested had antibodies suggesting NV infection. Although 12 of the 22 infected people (54.6%) were symptomatic, the remaining 10 (45.4%) were clinically well and had no past history of compatible pulmonary or neurological disease. Clinical and serological findings suggested three people had been infected with NV before the outbreak was recognized. All those who were infected were male abattoir workers. None of the people who had contact with horses, and no healthcare workers exposed to infected patients and their specimens had detectable antibodies. This study provides evidence that NV causes asymptomatic infection. All of the antibody positive individuals had direct contact with pigs and there was no evidence of human to human transmission.
OBJECTIVE: To study the incidence, aetiology, clinical characteristics and management of paediatric aseptic meningitis in a paediatric hospital in Singapore. MATERIALS AND METHODS: Patients with cerebrospinal fluid (CSF) pleocytosis, a negative Gram stain and bacterial culture were reviewed retrospectively from 1 January to 31 December 2000. Eighty-seven patients who fulfilled the criteria for aseptic meningitis and without neurological deficits were studied. In addition, reverse transcriptase polymerase chain reaction (RT-PCR) using pan enterovirus primers was subsequently performed on 73 of these CSF specimens which were available for storage. RESULTS: The incidence of aseptic meningitis was approximately 37 cases per 10,000 admissions. Non-polio enteroviruses were isolated from 29 of 64 (45.3%) CSF and 38 of 52 (73.1%) stool samples. RT-PCR was positive in 43 (58.9%) of the archived CSF specimens. The aetiologies of the remaining cases were mostly unidentified. Their ages ranged from 5 days to 12 years (median, 2 months). All patients except 1 had fever. Vomiting or poor feeding occurred in 44.7%, cough or running nose in 35.3%, irritability was observed in 35.3%, seizures in 7.1%, a rash in 10.6% and diarrhoea in 5.9%. All patients recovered without sequelae. The median CSF white cell count was 212 cells/mm3 (range, 7 to 12,000). The median glucose concentration was 2.7 mmol/L (range, 1.6 to 4.4). The median CSF/blood glucose ratio was 0.52 (range, 0.23 to 0.73). Median length of stay was 7 days (range, 4 to 17). Eighty-four patients (96.6%) received antibiotics for a median of 5.5 days (range, 2 to 14). CONCLUSION: Enteroviruses were the most common aetiologic agent identified. A method of early diagnosis using RT-PCR for enteroviruses is necessary to reduce the current duration of antibiotic usage and to decrease the length of hospital stay.
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INTRODUCTION: The landmark Paediatric AIDS Clinical Trials Group (PACTG) trial 076 showed in 1994 that antiretroviral therapy (ART) was effective in reducing maternal-child transmission of human immunodeficiency virus (HIV). This trial included antenatal oral zidovudine (ZDV), intrapartum intravenous ZDV, 6 weeks of oral ZDV to the babies and no breastfeeding. MATERIALS AND METHODS: This study is an on-going, prospective, open-label trial conducted from 1995 in which we enrolled HIV-infected pregnant women using the above strategy. Since 1997, the antenatal component of the regimen was modified to include lamivudine with ZDV. All babies had serial HIV polymerase chain reaction (PCR) and antibody tests including enzyme-linked immunosorbent assay (EIA), particle agglutination (PA) and Western blot (WB) at day 1, 1 week, 1, 2, 3, 6, 12 and 18 months. RESULTS: A total of 16 out of 19 eligible women were recruited from 1995 to 1999. The median age was 26 years (range 22 to 38 years), 38% were Singaporeans, median CD4 was 421 cells/mL (range 18 to 713 cells/mL) and median baseline gestational age was 23.5 weeks (range 8 to 32 weeks). None of the 16 children was infected as evidenced by 2 negative HIV PCRs including 1 done > 4 months old with a follow-up of 6 months to 2 years. There was a statistically significant difference between the 3 HIV antibody tests at 12 months of age (P = 0.003), there being more negative results with WB as compared to PA (P = 0.02). However, the difference between the 3 tests at 18 months was not statistically significant. No long-term side effects in these children were seen. CONCLUSION: Although the number of patients in this study is small, the absolute prevention of transmission (95% confidence intervals 0%-17%) in this cohort supports the recommendation of antenatal HIV screening and treatment of those infected.
CONTEXT: Current screening practices for blood donations have been successful in reducing human immunodeficiency virus (HIV) transmission through receipt of contaminated blood products. However, HIV-infected blood donations made prior to seroconversion and before high levels of viral replication occur could test negative using both serologic antigen and antibody tests. Testing based on nucleic acid amplification (NAT) is being implemented to screen for HIV-infected blood donated during this period, yet the issue of single vs minipool donation screening remains unresolved. OBJECTIVES: To determine HIV-1 genetic linkage between virus in 2 HIV-1-infected recipients of blood components and virus in the donor, who was HIV antigen and antibody negative at the time of donation; to screen the blood donor's plasma with HIV NAT assays, including those currently proposed for use in US blood donation screening. DESIGN AND SETTING: Case study conducted in October 1997 involving the Communicable Disease Centre, Singapore General Hospital, and the Singapore Blood Transfusion Service, Singapore. SUBJECTS: The blood donor and the 2 recipients of donor platelets and red blood cells. MAIN OUTCOME MEASURES: Genetic analysis of the HIV-1 p17 coding region of gag and the C2V5 region of env to determine the genetic relatedness of virus from the donor and recipients; reactivity in quantitative and qualitative assays, and reactivity in donor screening HIV NAT assays in single donation and minipool screening contexts. RESULTS: Direct DNA sequencing demonstrated identical HIV-1 subtype E viral sequences in the donor and recipients. Based on comparisons of a qualitative and quantitative assay for HIV-1 RNA levels, a low level of viremia (range, 5-39 copies/mL in plasma) was estimated to be in the donor's undiluted blood at the time of donation. Additional testing using donor-screening NAT assays showed consistent detection of HIV RNA in the undiluted donor plasma whereas detection was inconsistent at the 1:16 and 1:24 dilution levels currently used in minipool screening of blood donations in the United States. CONCLUSIONS: Transmission of HIV from a blood donor to a platelet recipient and a red blood cell recipient occurred in the preseroconversion infectious window period. The viral load in the implicated donation was estimated to be less than 40 copies/mL of plasma. Current US minipool HIV NAT screening protocols may not be sufficiently sensitive to detect all infectious window-period donations. JAMA. 2000;284:210-214
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A paramyxovirus virus termed Nipah virus has been identified as the etiologic agent of an outbreak of severe encephalitis in people with close contact exposure to pigs in Malaysia and Singapore. The outbreak was first noted in late September 1998 and by mid-June 1999, more than 265 encephalitis cases, including 105 deaths, had been reported in Malaysia, and 11 cases of encephalitis or respiratory illness with one death had been reported in Singapore. Electron microscopic, serologic, and genetic studies indicate that this virus belongs to the family Paramyxoviridae and is most closely related to the recently discovered Hendra virus. We suggest that these two viruses are representative of a new genus within the family Paramyxoviridae. Like Hendra virus, Nipah virus is unusual among the paramyxoviruses in its ability to infect and cause potentially fatal disease in a number of host species, including humans.
During 10-19 March 1999, 11 workers in 1 of 2 Singaporean abattoirs developed Nipah-virus associated encephalitis or pneumonia, resulting in 1 fatality. A case-control study was conducted to determine occupational risk factors for infection. Case patients were abattoir A workers who had anti-Nipah IgM antibodies; control subjects were randomly selected abattoir A workers who tested negative for anti-Nipah IgM. All 13 case patients versus 26 (63%) of 41 control subjects reported contact with live pigs (P=.01). Swine importation from Malaysian states concurrently experiencing a Nipah virus outbreak was banned on 3 March 1999; on 19 March 1999, importation of Malaysian pigs was banned, and abattoirs were closed. No unusual illnesses among pigs processed during February-March were reported. Contact with live pigs appeared to be the most important risk factor for human Nipah virus infection. Direct contact with live, potentially infected pigs should be minimized to prevent transmission of this potentially fatal zoonosis to humans.
Polyclonal antibodies derived from dengue virus immune sera and 3H5 monoclonal antibody showed potent neutralisation effect on dengue-2 virus in the plaque reduction neutralisation assay. This study demonstrated that antibodies present in immune human sera and 3H5 monoclonal antibody neutralised dengue-2 virus by altering the virus entry pathway into cells. In the presence of neutralising antibodies, dengue-2 virus was endocytosed by LLC-MK2 cells. The endocytosis process involved ruffling of antibody-coated virions by cellular pseudopodia and invagination of cell membrane. This mode of entry is atypical as compared to direct fusion of dengue-2 virus with cell membrane in the absence of antibody. The virions were internalised in the form of virion-antibody complexes consisting of single or clumps of virions. After 3 minutes of incubation, neutralised virions were detected in cellular vesicles, and signs of intra-endosomal penetration into cytoplasm were not evident even after a prolonged incubation of 10 minutes, suggesting that viral uncoating was compromised. Vesicle-bound virions were no longer detected after 20 minutes of incubation. In addition, no sign of viral replication was detected in cells infected with "neutralised" virions by immunofluorescence assay. This indicated that internalised virions had been degraded leading to abortive infection. In conclusion, antibodies present in 3H5 monoclonal antibody and human immune sera rendered dengue-2 virus non-infective by neutralising the viral fusion site and causing alteration of viral entry mode. Antibodies in immune sera but not 3H5 monoclonal antibody also exerted minimal inhibitory effect on virus binding and internalisation.
A specific and sensitive method based on RT-PCR was developed to detect enterovirus 71 (EV71) from patients with hand, foot and mouth disease, myocarditis, aseptic meningitis and acute flaccid paralysis. RT-PCR primers from conserved parts of the VP1 capsid gene were designed on the basis of good correlation with sequences of EV71 strains. These primers successfully amplified 44 strains of EV71 including 34 strains isolated from Singapore in 1997 and 1998, eight strains from Malaysia isolated in 1997 and 1998, one Japanese strain and the neurovirulent strain EV71/7423/MS/87. RT-PCR of 30 strains of other enteroviruses including coxsackievirus A and B, and echoviruses failed to give any positive amplicons. Hence, RT-PCR with these primers showed 100% correlation with serotyping. Direct sequencing of the RT-PCR products of 20 EV71 strains revealed a distinct cluster with two major subgroups, thus enabling genetic typing of the viruses. The genetic heterogeneity of these strains culminated in amino acid substitutions within the VP1, VP2 and VP3 regions. The sequencing of a 2.9 kb fragment comprising the capsid region and the major part of 5' UTR of two Singapore strains revealed that they belonged to a group distinct from the prototype EV71/BrCr strain and the EV71/7423/MS/87 strain. The dendrogram generated from 341 bp fragments within the VP1 region revealed that the strains of Singapore, Malaysia and Taiwan belong to two entirely different EV71 genogroups, distinct from the three genogroups identified in another recent study.
INTRODUCTION: The pathogenic importance of antineutrophil cytoplasmic antibodies (ANCAs) in inflammatory bowel disease (IBD) is unclear and target antigen localisation studies may lend insight to the specific pathogenic mechanisms of IBD. In this pilot study, we looked at occurrence of ANCA in Asian IBD patients. In ANCA-positive samples, we analysed for the presence of target antigens i.e. proteinase 3, lactoferrin, myeloperoxidase, elastase, cathepsin G and lysozyme. MATERIALS AND METHODS: This prospective study was carried out from July 1997 to February 1998. Sera were screened for ANCAs with indirect immunofluorescent test and tested with an enzyme immunoassay (ELISA) kit which provides a semi-quantitative assay for human IgG autoantibodies against 6 antigens: proteinase 3, lactoferrin, myeloperoxidase, elastase, cathepsin G and lysozyme. RESULTS: A total of 75 patients were studied: 50 with IBD and 25 controls with functional bowel disease. Ten had Crohn's disease (CD) and 40 had ulcerative colitis (UC). There was no racial predilection among the Chinese, Malays or Indians. In CD, 1 was positive for cytoplasmic ANCA (cANCA) and 2 for perinuclear ANCA (pANCA). In UC, 4 were positive for pANCA, 15 for atypical perinuclear ANCA (apANCA) and 1 for cANCA. In the CD and UC population, the proportion positive for ANCA was 30% and 50%, respectively. There was no ANCA detected among the controls. Of those ANCA-positive IBD patients (n:23), only 1 demonstrated anti-myeloperoxidase antibodies. No antibodies were detected against the other 5 antigens tested. CONCLUSIONS: This pilot Singapore study concludes that there is no significant ANCA association with proteinase 3, lactoferrin, myeloperoxidase, elastase, cathepsin G and lysozyme.
INTRODUCTION: Quantitative measurement of plasma HIV-1 RNA viral load has been available in Singapore since 30 November 1996. This study investigates the relationship, in antiretroviral-naïve, HIV-positive Singapore residents, between the baseline HIV-1 RNA viral load and clinical status at the time of quantification. The association of HIV-1 RNA viral load with CD4+ T-cell counts was also studied. MATERIALS AND METHODS: HIV-1 RNA viral load was determined using Amplicor HIV-1 Monitor Test. One hundred and eighty subjects had baseline plasma HIV-1 RNA levels quantified during the period 30 November 1996 to 27 July 1998. They were classified into three clinical groups: A for asymptomatic infection (n = 110), B for symptomatic infection (n = 29) and C for AIDS (n = 41). RESULTS: The differences between mean HIV-1 RNA levels were statistically significant (P < 0.001) for groups A and B (mean difference = -0.61 log10), and for groups A and C (mean difference = -0.75 log10). However, there was no statistically significant difference (P = 0.68) between groups B and C (mean difference = -0.13 log10). Of those subjects with CD4+ T-cell counts measured within 30 days of viral load quantification, there were statistically significant negative correlations between HIV-1 viral load and CD4+ T-cell counts for groups A (n = 91, r = -0.536, P < 0.01) and C (n = 34, r = -0.446, P < 0.01) but not group B (n = 26, r = -0.297, P > 0.05). CONCLUSION: This suggest that the more advanced the phase of HIV infection, the higher the baseline plasma viral load and the lower the CD4+ T-lymphocyte counts.
BACKGROUND: In March 1999, an outbreak of encephalitis and pneumonia occurred in workers at an abattoir in Singapore. We describe the clinical presentation and the results of investigations in these patients. METHODS: Clinical and laboratory data were collected by systemic review of the case records. Serum and cerebrospinal fluid (CSF) samples were tested for IgM antibodies to Nipah virus with an IgM capture ELISA. Reverse-transcriptase PCR was done on the CSF and tissue samples from one patient who died. FINDINGS: Eleven patients were confirmed to have acute Nipah-virus infection based on raised IgM in serum. Nipah virus was identified by reverse transcriptase PCR in the CSF and tissue of the patient who died. The patients were all men, with a median age of 44 years. The commonest presenting symptoms were fever, headache, and drowsiness. Eight patients presented with signs of encephalitis (decreased level of consciousness or focal neurological signs). Three patients presented with atypical pneumonia, but one later developed hallucinations and had evidence of encephalitis on CSF examination. Abnormal laboratory findings included a low lymphocyte count (nine patients), low platelet count, low serum sodium, and high aspartate aminostransferase concentration (each observed in five patients). The CSF protein was high in eight patients and white-blood-cell count was high in seven. Chest radiography showed mild interstitial shadowing in eight patients. Magnetic resonance imaging (MRI) showed focal areas of increased signal intensity in the cortical white marker in all eight patients who were scanned. The nine patients with encephalitis received empirical treatment with intravenous aciclovir and eight survived. INTERPRETATION: Infection with Nipah virus caused an encephalitis illness with characteristic focal areas of increased intensity seen on MRI. Lung involvement was also common, and the disease may present as an atypical pneumonia.