Displaying publications 1 - 20 of 100 in total

  1. Chua KB
    PMID: 22782307 DOI: 10.1007/82_2012_218
    Until the Nipah outbreak in Malaysia in 1999, knowledge of human infections with the henipaviruses was limited to the small number of cases associated with the emergence of Hendra virus in Australia in 1994. The Nipah outbreak in Malaysia alerted the global public health community to the severe pathogenic potential and widespread distribution of these unique paramyxoviruses. This chapter briefly describes the initial discovery of Nipah virus and the challenges encountered during the initial identification and characterisation of the aetiological agent responsible for the outbreak of febrile encephalitis. The initial attempts to isolate Nipah virus from the bat reservoir host are also described.
  2. Chua KB
    Med J Malaysia, 2010 Dec;65(4):277-82.
    PMID: 21901945 MyJurnal
    This is a retrospective cross-sectional study based on the database of clusters of patients with clinical diagnosis of chikungunya (CHIK) that were referred to the National Public Health Laboratory for diagnostic investigations from January 2006 to December 2009. Of the 13,759 referred patients, a total of 6314 (45.9%) patients were laboratory confirmed to have CHIK and 7445 (54.1) patients were considered as clinical cases of CHIK by epidemiological link. Epidemic curves plotted using date of onset of illness for all referred clusters of cases showed that there were three unrelated outbreaks of CHIK in Malaysia from 2006 to 2009. There were two small outbreaks that occurred within the state of Perak in 2006. The cluster of cases in 2008 and 2009 were of related outbreak which started in Johor state and subsequently spread to various parts of Malaysia. The mean age of the patients was 37.0 years old and those patients in the laboratory confirmed group were significantly younger than those in the epidemiological linked group. The main presenting clinical features recorded in this study were fever, arthralgia, myalgia and rashes. Those patients in the laboratory confirmed group had a significant higher incidence of fever, arthralgia and rash than those in the epidemiological linked group.
  3. Chua KB
    Malays J Pathol, 2010 Dec;32(2):75-80.
    PMID: 21329177 MyJurnal
    An outbreak of acute febrile encephalitis affecting pig-farm workers and owners was recognized in peninsular Malaysia as early as September 1998. The outbreak was initially thought to be due to Japanese encephalitis (JE) virus and thus very intensive prevention, control and communication strategies directed at JE virus were undertaken by the Ministry of Health and Ministry of Agriculture of Malaysia. There was an immediate change in the prevention, control and communication strategies with focus and strategies on infected pigs as the source of infections for humans and other animals following the discovery of Nipah virus. Information and understanding the risks of Nipah virus infections and modes of transmission strengthened the directions of prevention, control and communication strategies. A number of epidemiological surveillances and field investigations which were broadly divided into 3 groups covering human health sector, animal health sector and reservoir hosts were carried out as forms of risk assessment to determine and assess the factors and degree of risk of infections by the virus. Data showed that there was significant association between Nipah virus infection and performing activities involving close contact with pigs, such as processing of piglets, administering injection or medication to pigs, assisting in the birth of piglets, assisting in pig breeding, and handling of dead pigs in the affected farms. A complex process of anthropogenic driven deforestation, climatic changes brought on by El Niño-related drought, forest fire and severe haze, and ecological factors of mixed agro-pig farming practices and design of pig-sties led to the spillovers of the virus from its wildlife reservoir into pig population.
  4. Chua KB
    Malays J Pathol, 2010 Dec;32(2):69-73.
    PMID: 21329176 MyJurnal
    The outbreak of Nipah virus, affecting pigs and pig-farm workers, was first noted in September 1998 in the north-western part of peninsular Malaysia. By March 1999, the outbreak had spread to other pig-farming areas of the country, inclusive of the neighbouring country, Singapore. A total of 283 human cases of viral encephalitis with 109 deaths were recorded in Malaysia from 29 September 1998 to December 1999. During the outbreak period, a number of surveillances under three broad groups; Surveillance in Human Health Sector, Surveillance in Animal Health Sector, and Surveillance for the Reservoir Hosts, were carried out to determine the prevalence, risk of virus infections and transmission in human and swine populations as well as the source and reservoir hosts of Nipah virus. Surveillance data showed that the virus spread rapidly among pigs within infected farms and transmission was attributed to direct contact with infective excretions and secretions. The spread of the virus among pig farms within and between states of peninsular Malaysia was due to movement of pigs. The transmission of the virus to humans was through close contact with infected pigs. Human to human transmission was considered a rare event though the Nipah virus could be isolated from saliva, urine, nasal and pharyngeal secretions of patients. Field investigations identified fruitbats of the Pteropid species as the natural reservoir hosts of the viruses. The outbreak was effectively brought under control following the discovery of the virus and institution of correct control measures through a combined effort of multi-ministerial and multidisciplinary teams working in close co-operation and collaboration with other international agencies.
  5. Chua KB
    Microbes Infect., 2003 May;5(6):487-90.
    PMID: 12758277
    During the outbreak of Nipah virus encephalitis involving pigs and humans in peninsular Malaysia in 1998/1999, a conventional approach was initially undertaken to collect specimens from fruit bats by mist-netting and shooting, as an integral part of wildlife surveillance of the natural reservoir host of Nipah virus. This study describes a novel method of collecting fruit bats' urine samples using plastic sheets for isolation of Nipah virus. This novel approach resulted in the isolation of several other known and unidentified infectious agents besides Nipah virus.
  6. Chua KB
    J Clin Virol, 2003 Apr;26(3):265-75.
    PMID: 12637075
    Nipah virus, a novel paramyxovirus, closely related to Hendra virus emerged in northern part of Peninsular Malaysia in 1998. The virus caused an outbreak of severe febrile encephalitis in humans with a high mortality rate, whereas, in pigs, encephalitis and respiratory diseases but with a relatively low mortality rate. The outbreak subsequently spread to various regions of the country and Singapore in the south due to the movement of infected pigs. Nipah virus caused systemic infections in humans, pigs and other mammals. Histopathological and radiological findings were characteristic of the disease. Fruitbats of Pteropid species were identified as the natural reservoir hosts. Evidence suggested that climatic and anthropogenic driven ecological changes coupled with the location of piggeries in orchard and the design of pigsties allowed the spill-over of this novel paramyxovirus from its reservoir host into the domestic pigs and ultimately to humans and other animals.
  7. Chua KB
    Med J Malaysia, 1999 Mar;54(1):58-64.
    PMID: 10972006
    A 10-year follow-up of children having exanthem subitum (ES) seen in an outpatient paediatric clinic, Kuala Lumpur, Malaysia shows that uvulo-palatoglossal junctional (UPJ) ulcer is a reliable early clinical sign of ES. During this period, 1,977 children (1,086 males, 891 females) had adequate follow-up from the age of 3 months to 24 months old. 897 children (478 males, 419 females) were noted to have UPJ ulcers. Of these 897 children, 855 (459 males, 396 females) presented with the classical clinical features of ES of maculopapular rash following 3 to 4 days of fever. The positive predictive value and the negative predictive value of UPJ ulcers in the clinical diagnosis of ES are 95.3% and 100% respectively. Among the 855 children with clinical features of ES, a provisional diagnosis of ES could be made in 781 children during the pre-eruptive phase by the presence of the UPJ ulcers. The other 74 children already had the rash at the time of consultation at the clinic. The peak age of occurrence of ES was 6 months old with 98.2% of the total cases of ES seen between the age of 4 and 12 months. There was no significant gender difference in the incidence of ES nor any seasonal variation. Mild to moderate diarrhoea was the other commonly associated clinical feature which usually presented from the third febrile day onwards.
    Study site: Paediatric clinic, Assunta Hospital, Petaling Jaya, Selangor, Malaysia
  8. Chua KB, Kasri AR
    Virol Sin, 2011 Aug;26(4):221-8.
    PMID: 21847753 DOI: 10.1007/s12250-011-3195-8
    Hand foot and mouth disease is a febrile sickness complex characterized by cutaneous eruption (exanthem) on the palms and soles with simultaneous occurrence of muco-cutanous vesiculo-ulcerative lesions (enanthem) affecting the mouth. The illness is caused by a number of enteroviruses with coxsackievirus A16 and enterovirus 71 as the main causative agents. Human enterovirus 71 (EV71) belongs to the species Human enterovirus A under the genus Enterovirus within the family Picornaviridae. EV71 has been associated with an array of clinical diseases including hand foot and mouth disease (HFMD), aseptic meningitis, encephalitis and poliomyelitis-like acute flaccid paralysis. A large outbreak of HFMD due to highly neurovirulent EV71 emerged in Malaysia in 1997, and caused 41 deaths amongst young children. In late 2000, a recurrence of an outbreak of HFMD occurred in Malaysia with 8 fatalities in peninsular Malaysia. Outbreak of HFMD due to EV71 recurred in 2003 with an unknown number of cases and mortalities. A similar outbreak of HFMD with 2 recorded deaths in young children occurred in peninsular Malaysia in late 2005 and this was followed by a larger outbreak in Sarawak (Malaysian Borneo) with 6 reported fatalities in the early part of 2006. The current on-going outbreak of HFMD started in peninsular Malaysia in epidemiological week 12 of 2010. As with other HFMD outbreaks in Malaysia, both EV71 and CA16 were the main aetiological viruses isolated. In similarity with the HFMD outbreak in 2005, the isolation of CA16 preceded the appearance of EV71. Based on the VP1 gene nucleotide sequences, 4 sub-genogroups of EV71 (C1, C2, B3 and B4) co-circulated and caused the outbreak of hand, foot and mouth disease in peninsular Malaysia in 1997. Two sub-genogroups (C1 and B4) were noted to cause the outbreak in 2000 in both peninsular Malaysia and Sarawak. EV71 of sub-genogroup B5 with smaller contribution from sub-genogroup C1 caused the outbreak in 2003. In the 2005 outbreak, besides the EV71 strains of sub-genogroup C1, EV71 strains belonging to sub-genogroup B5 were isolated but formed a cluster which was distinct from the EV71 strains from the sub-genogroup 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 sub-genogroup B5. Phylogenetic analysis of the VP1 gene suggests that the EV71 strains causing the outbreak in Sarawak could have originated from peninsular Malaysia. Epidemiological and molecular data since 1997 show the recurrence of HFMD due to EV71 in Malaysia every 2 to 4 years. In each of the past outbreaks, more than one sub-genogroup of the virus co-circulate.
  9. Looi LM, Chua KB
    Malays J Pathol, 2007 Dec;29(2):63-7.
    PMID: 19108397 MyJurnal
    The Nipah virus outbreak in Malaysia (September 1998 to May 1999) resulted in 265 cases of acute encephalitis with 105 deaths, and near collapse of the billion-dollar pig-farming industry. Because it was initially attributed to Japanese encephalitis, early control measures were ineffective, and the outbreak spread to other parts of Malaysia and nearby Singapore. The isolation of the novel aetiological agent, the Nipah virus (NiV), from the cerebrospinal fluid of an outbreak victim was the turning point which led to outbreak control 2 months later. Together with the Hendra virus, NiV is now recognised as a new genus, Henipavirus (Hendra + Nipah), in the Paramyxoviridae family. Efforts of the local and international scientific community have since elucidated the epidemiology, clinico-pathophysiology and pathogenesis of this new disease. Humans contracted the infection from close contact with infected pigs, and formed the basis for pig-culling that eventually stopped the outbreak. NiV targeted medium-sized and small blood vessels resulting in endothelial multinucleated syncytia and fibrinoid necrosis. Autopsies revealed disseminated cerebral microinfarctions resulting from vasculitis-induced thrombosis and direct neuronal involvement. The discovery of NiV in the urine and saliva of Malaysian Island flying foxes (Pteropus hypomelanus and Petropus vampyrus) implicated these as natural reservoir hosts of NiV. It is probable that initial transmission of NiV from bats to pigs occurred in late 1997/early 1998 through contamination of pig swill by bat excretions, as a result of migration of these forest fruitbats to cultivated orchards and pig-farms, driven by fruiting failure of forest trees during the El Nino-related drought and anthropogenic fires in Indonesia in 1997-1998. This outbreak emphasizes the need for sharing information of any unusual illnesses in animals and humans, an open-minded approach and close collaboration and co-ordination between the medical profession, veterinarians and wildlife specialists in the investigation of such illnesses. Environmental mismanagement (such as deforestation and haze) has far-reaching effects, including encroachment of wildlife into human habitats and the introduction of zoonotic infections into domestic animals and humans.
  10. Lam SK, Chua KB
    Clin Infect Dis, 2002 May 1;34 Suppl 2:S48-51.
    PMID: 11938496 DOI: 10.1086/338818
    Emerging infectious diseases involving zoonosis have become important global health problems. The 1998 outbreak of severe febrile encephalitis among pig farmers in Malaysia caused by a newly emergent paramyxovirus, Nipah virus, is a good example. This disease has the potential to spread to other countries through infected animals and can cause considerable economic loss. The clinical presentation includes segmental myoclonus, areflexia, hypertension, and tachycardia, and histologic evidence includes endothelial damage and vasculitis of the brain and other major organs. Magnetic resonance imaging has demonstrated the presence of discrete high-signal-intensity lesions disseminated throughout the brain. Nipah virus causes syncytial formation in Vero cells and is antigenically related to Hendra virus. The Island flying fox (Pteropus hypomelanus; the fruit bat) is a likely reservoir of this virus. The outbreak in Malaysia was controlled through the culling of >1 million pigs.
  11. Tan CT, Chua KB
    Curr Infect Dis Rep, 2008 Jul;10(4):315-20.
    PMID: 18765105
    Nipah virus was first discovered in 1999, after a severe outbreak of viral encephalitis among pig farm workers in Malaysia. The disease is thought to spread from Pteropus bats to pigs and then to humans following close contact. The reported mortality rate in this outbreak was 40%. The main necropsy finding in patients with Nipah virus encephalitis was disseminated microinfarction associated with vasculitis and direct neuronal involvement. Relapse of encephalitis was seen in 10% of those who survived the initial illness. Since that initial report, recurrent outbreaks of Nipah virus encephalitis have been seen in Bangladesh and West Bengal, India. These outbreaks occurred between January and May, with Pteropus giganteus as a reservoir of the virus. In Bangladesh, the virus probably spread directly from bats to humans-with human to human spread as another important mode of infection-and the mortality rate was 70%.
  12. Ang KT, Ruhaini I, Chua KB
    Med J Malaysia, 2006 Aug;61(3):292-5.
    PMID: 17240578 MyJurnal
    Dengue fever is major public health problem especially among the highly urbanized states of Malaysia, such as, Selangor and Kuala Lumpur Federal Territory. We report an epidemiological cluster pattern of dengue outbreak in the district of Gombak, Selangor that may mimic other acute febrile illnesses in which the transmission mode is via close contact. This dengue outbreak consisted of two waves; an initial cluster of three cases (including the first deceased, JI) which occurred between 20th and 21st of July, followed by a later larger cluster of 11 cases that occurred between 1st and 8th of August 2005. This epidemiological clustering pattern of acute dengue virus infection among close contacts suggests an intense rate of dengue virus transmission within the vicinity of the first deceased's house.
  13. Chua KB, Chua BH, Wang CW
    Malays J Pathol, 2002 Jun;24(1):15-21.
    PMID: 16329551
    In late 1998, a novel paramyxovirus named Nipah virus, emerged in Malaysia, causing fatal disease in domestic pigs and humans with substantial economic loss to the local pig industry. Pteropid fruitbats have since been identified as a natural reservoir host. Over the last two decades, the forest habitat of these bats in Southeast Asia has been substantially reduced by deforestation for pulpwood and industrial plantation. In 1997/1998, slash-and-burn deforestation resulted in the formation of a severe haze that blanketed much of Southeast Asia in the months directly preceding the Nipah virus disease outbreak. This was exacerbated by a drought driven by the severe 1997-1998 El Niño Southern Oscillation (ENSO) event. We present data suggesting that this series of events led to a reduction in the availability of flowering and fruiting forest trees for foraging by fruitbats and culminated in unprecedented encroachment of fruitbats into cultivated fruit orchards in 1997/1998. These anthropogenic events, coupled with the location of piggeries in orchards and the design of pigsties allowed transmission of a novel paramyxovirus from its reservoir host to the domestic pig and ultimately to the human population.
  14. Chua KB, Lam SK, AbuBakar S
    Med J Malaysia, 1998 Sep;53(3):296-301.
    PMID: 10968172
    Exanthem subitum (ES) is a common childhood exanthematous disease. In a recent study of ES due to human herpesvirus 6 (HHV 6), we isolated human herpesvirus 7 (HHV 7) from the peripheral blood mononuclear cells (PBMC) of a seven month-old infant with typical symptoms of ES. The identity of the virus was confirmed by indirect immunofluorescence using HHV 7 specific monoclonal antibody and by amplification of the HHV 7 specific genomic sequences using the polymerase chain reaction (PCR). Paired serum samples from the infant showed serological conversion to the isolated virus. The clinical manifestations of ES in this infant appeared to be milder than the classical ES due to HHV 6.
  15. Chua KB, Khairullah NS, Hooi PS
    PMID: 9031408
    Sera from healthy donors and patients stored over a period of 2 years, aged 1 to 83 years, were examined for reactivity to human herpes virus 6 (HHV-6) by the standard indirect immunofluorescence assay (IFA). Of the 600 serum specimens screened, 502 showed positive reactivity to HHV-6. This gives an overall seropositive rate of 83.7%. There is no significant difference in the overall positive rate between the ethnic groups (Chinese, Malays, Indians) (chi 2 = 0.35 df = 2 p > 0.05). However, there is significant difference in the positive rates at the extreme age groups of 1 year as well as 61 years and above. From birth up to below 1 year of age, the seroprevalence rate was 82%. At one year of age the positive rate decreased to 66% before gradually rising so that the percentage seropositivity of 6 to 10 years old becomes similar to that in older children and adults (11 to 40 years). The positive rate then starts to decline after 40 years of age. Using a standardized scoring system, the corresponding antibody titer was found to be high in the very young population and starts to decline after the age of 15 years. This suggests that in our population group, primary infection occurs mainly in the pediatric age group. It also accounts for the low positive rate in the age group of 61 years and above, as by then the titer had fallen to the level below the detection limits of the assay system.
  16. 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.
  17. Omar M, Zaliza S, Mariappan M, Zainal AO, Chua KB
    Malays J Pathol, 2011 Dec;33(2):113-7.
    PMID: 22299212 MyJurnal
    A field evaluation on the effectiveness of a modified approach of chemical fogging of insecticides against the conventional method was carried out in the Seremban district within the state of Negeri Sembilan, Malaysia from 7th February 2003 to 7th September 2003. In the 3 months period, November 2002 to January 2003, prior to institution of modified approach of chemical fogging, 27 of 42 (64.3%) dengue outbreaks were successfully controlled within the stipulated time frame of 14 days by the conventional approach of thermal chemical fogging. However, during the period when the modified approach of chemical fogging was instituted, 25 of 27 (92.6%) dengue outbreaks within the same district were successfully controlled within the 14-days time-line. Statistically, the modified approach of chemical fogging significantly improved the success rate of achieving dengue outbreak control within the stipulated time frame (chi2 = 5.65, p = 0.01745). The modified approach of chemical fogging also appeared to reduce the number of dengue cases recorded in the same district. This small pilot study shows that the modified approach of chemical fogging reduced cost in carrying out each fogging activity to control dengue outbreak. It also substantially reduced the required time taken to complete each fogging activity in comparison to the conventional approach. Thus, it enabled similar number of workers to cover more localities simultaneously affected by the outbreaks. In addition, the modified approach reduced the exposure time to hazardous insecticides for each worker doing hand-held thermal fogging.
  18. Bina Rai S, Wan Mansor H, Vasantha T, Norizah I, Chua KB
    Med J Malaysia, 2007 Aug;62(3):223-6.
    PMID: 18246912 MyJurnal
    Confinement homes are private institutions that provide full-time care for newborn babies and their respective postpartum mothers up to one month after delivery. An outbreak of fever and diarrhoea amongst newborns occurred in one such confinement home in Penang between the months of September to October 2004. An outbreak investigation was carried out including all babies, their respective mothers and workers in the home to determine the source of the outbreak and to institute control measures. Based on a working case definition of febrile illness with or without diarrhoea, 11 out of the 13 babies in the confinement home met the case definition. One hundred percent had symptoms of fever. 36.4% had symptoms of diarrhea and other respiratory conditions respectively. The attack rate of among babies in the confinement home was 90%. Echovirus 11 was isolated from 3 out of the 11 febrile cases. Echovirus 11 was isolated from the cerebrospinal fluid and stool of another baby at a private hospital that was epidemiologically linked to the first case. In conclusion, the outbreak of febrile illness amongst newborn babies in the affected confinement home was due to echovirus 11. The source was probably health-care associated with efficient transmission within the confinement home. The faecal-oral route was the most likely mode of transmission.
  19. 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.
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