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At least 721 records · Page 40Linked to original sources
PubMed2006

Dengue maculopathy: a case report.

INTRODUCTION: Dengue fever is endemic in many countries of South East Asia. In spite of the occasional epidemics, dengue maculopathy remains a rare entity. CASE HISTORY: A 31-year-old gentleman was admitted with a 6-day history of fever, generalised rash, headache and myalgia after a trip to Malaysia. There were no bleeding manifestations. The lowest platelet count was 71 x 10,000/ml, the haematocrit was 42.7%, and dengue serology was positive. On the 8th day of illness, he complained of bilateral blurred vision. Detailed visual examination showed visual acuity of right eye 6/30 and left eye 6/50. Fundoscopy revealed dilated veins, hyperaemic optic discs, flame and blot haemorrhages, soft exudates and macular ischaemia. After a course of high-dose steroids, the visual acuity as well as colour vision improved markedly. DISCUSSION: The pathology of maculopathy is not obvious in this case, but an immunological reaction is suspected. There is a risk of residual visual impairment, and there is no definitive treatment. The use of high-dose steroids seemed to improve visual acuity and colour vision. However, it is not known whether immunosuppression improves the prognosis. Time for resolution is from 8 weeks to 4 months. Since there is an increase in the incidence of dengue fever in our region, coupled with rising international travel, one could postulate that global incidence of dengue-related maculopathy may become significant. CONCLUSION: Ocular complications associated with dengue fever are rare but may result in permanent visual impairment. Dengue fever should be suspected in travellers, particularly those returning from endemic areas, and they should be systematically screened for maculopathy when visual disturbances arise.

Adult↗
PubMed2002

Potential effect of population and climate changes on global distribution of dengue fever: an empirical model.

BACKGROUND: Existing theoretical models of the potential effects of climate change on vector-borne diseases do not account for social factors such as population increase, or interactions between climate variables. Our aim was to investigate the potential effects of global climate change on human health, and in particular, on the transmission of vector-borne diseases. METHODS: We modelled the reported global distribution of dengue fever on the basis of vapour pressure, which is a measure of humidity. We assessed changes in the geographical limits of dengue fever transmission, and in the number of people at risk of dengue by incorporating future climate change and human population projections into our model. FINDINGS: We showed that the current geographical limits of dengue fever transmission can be modelled with 89% accuracy on the basis of long-term average vapour pressure. In 1990, almost 30% of the world population, 1.5 billion people, lived in regions where the estimated risk of dengue transmission was greater than 50%. With population and climate change projections for 2085, we estimate that about 5-6 billion people (50-60% of the projected global population) would be at risk of dengue transmission, compared with 3.5 billion people, or 35% of the population, if climate change did not happen. INTERPRETATION: We conclude that climate change is likely to increase the area of land with a climate suitable for dengue fever transmission, and that if no other contributing factors were to change, a large proportion of the human population would then be put at risk.

Aedes↗
PubMed2003

Production of anti-dengue NS1 monoclonal antibodies by DNA immunization.

Monoclonal antibodies against dengue NS1 protein were generated following immunization of mice with plasmid DNA encoding the transmembrane form of NS1 from dengue serotype 2 virus. A mammalian expression vector, pDisplay, was engineered to direct cell surface expression of dengue NS1 and tested for transient expression in COS cells. Two mice were immunized intramuscularly with six doses of 100 microg of plasmid at 2-week intervals; one mouse received a booster of live virus prior to the last plasmid injection. Both mice showed antibody responses against dengue antigens in dot enzyme immunoassay. Following fusion, hybridomas were screened with dot enzyme immunoassay against all four dengue serotypes. Specificity to the NS1 protein was confirmed by western blot analysis. Among five anti-dengue NS1 monoclonal antibodies generated, two clones were serotype 2 specific, two clones reacted with all four serotypes and the last also reacted with Japanese encephalitis virus. Reactivity against native or denatured forms of NS1 revealed three clones with reactivity to linear epitopes and two clones recognizing conformational epitopes. Such diverse specificity of anti-dengue NS1 monoclonal antibodies indicates that DNA immunization, especially with the combination of virus boosting, is an efficient way of producing monoclonal antibodies against viral protein. This has opened up a possibility of producing monoclonal antibodies to rare viral proteins that are difficult to isolate or purify.

Animals↗
PubMed2003

Evidence for in vitro falsely-primed cDNAs that prevent specific detection of virus negative strand RNAs in dengue-infected cells: improvement by tagged RT-PCR.

The identification of cell types replicating dengue viruses is an important step towards the understanding of the pathophysiology of dengue severe forms. Since the detection of negative strand viral RNAs is the more reliable marker of active replication for single-strand positive sense RNA viruses, we reassessed the specificity of RT-PCR assays already developed to detect dengue negative strand RNAs. Studying mammalian Vero cells infected by a dengue-2 strain, it was shown that falsely-primed cDNAs are generated in vitro during the reverse transcription step and are amplified subsequently by PCR. Since this may compromise the specificity of existing RT-PCR systems, we developed a tagged RT-PCR assay and addressed the role of some critical factors in such a system. Optimization of the negative strand-specific tagged RT-PCR allowed to resolve the problems due to the PCR amplification of falsely-primed cDNAs. Using this assay it was possible to detect specifically negative strand RNAs as soon as 3h after Vero cells have been exposed to the dengue-2 strain and we showed that this system is highly specific. Thus, the present dengue negative strand-specific tagged RT-PCR assay may help to reassess viral replication in the context of dengue pathophysiology.

Animals↗
PubMed2005

Specific IgM and IgG responses in primary and secondary dengue virus infections determined by enzyme-linked immunosorbent assay.

IgM- and IgG-capture ELISAs are widely used as diagnostic tests for confirmation of dengue virus infection. The positive rate of anti-dengue IgM and IgG detection was examined in primary and secondary dengue virus infections in the setting of a provincial hospital using IgM- and IgG-capture ELISAs. Disease day 1 was defined as the day of onset of symptoms. In total, 232 plasma samples were collected from 106 confirmed dengue cases consisting of 12 primary and 94 secondary infections. In primary infection, anti-dengue IgM was detected in 4 out of 5 samples collected on disease day 5 and in all the 21 samples collected on disease day 6 or later. Specific IgG was detected in 2 out of 5 samples collected on day 12, and in 5 out of 6 samples collected on disease days 13-15, but was not detected in samples collected on disease day 10 or earlier. In secondary infection, IgM was not detected in the samples on disease days 2 and 3, but detected in 20 out of 79 samples collected on days 4-6, in 44 out of 65 on disease days 7-11 and in 40 out of 51 samples on disease days 12-14. In contrast, specific IgG was detected in 21 out of 60 samples on disease days 4 and 5, in 13 out of 19 on disease day 6, in 62 out of 65 on disease days 7-11 and in all the samples collected on disease day 12 or later. The result indicate that seroconversion rates of IgM and IgG are different between primary and secondary infections, and suggest that detection of specific IgM and IgG is necessary for determining dengue virus infection and for differentiating primary and secondary dengue infections.

Adolescent↗
PubMed2007

Production, purification and characterization of recombinant dengue multiepitope protein.

Dengue is an acute mosquito-borne viral disease of humankind. Dengue fever, dengue haemorrhagic fever and dengue shock syndrome have become global public health problems in recent years. rDME-G (recombinant dengue multiepitope protein that can specifically detect IgG) was produced in a 5-litre fermenter in Escherichia coli for use in diagnosis. The culture was induced with 1 mM isopropyl beta-D-thiogalactoside and cells were further grown for 4 h before harvesting. After fermentation, dry cell weight resulted in approx. 16.2 g/l. The rDME-G protein was purified from inclusion bodies using affinity chromatography. The final yield of purified rDME-G protein from fermentation resulted in approx. 168 mg/l of pure biologically active rDME-G protein. The purity of rDME-G protein was checked by SDS/PAGE analysis and the reactivity of this protein was further determined by Western blotting. The purified protein was used to develop an in-house dipstick ELISA and tested using a panel of 60 patient sera characterized using the commercially available tests for detection of dengue antibody. We compared our results with IgG-capture ELISA (Pan-Bio, Windsor, QLD, Australia) and rapid IC (immuno-chromatography) test (Pan-Bio). By using rDME-G protein as an antigen, in the dipstick ELISA, the results were in excellent agreement with commercial rapid IC test and IgG capture ELISA. These results show that the product has a promising potential to be used for diagnosis of dengue in both laboratory- and field-based detection systems with minimum cost and a high degree of sensitivity and specificity.

Dengue Virus↗
PubMed2004

Seroepidemiology of dengue in the adult population of Singapore.

Urbanization is one of the reasons for the resurgence of dengue in tropical and subtropical countries. We conducted a cross-sectional seroepidemiological study in Singapore to determine the extent at which the Singapore population has been exposed to dengue infections. Dengue antibodies were measures with PanBio Dengue. Of 298 enrolled subjects (age 18-45), 133 (45%) had a positive dengue serology. In multivariate analysis, age and nationality (Singaporean vs non-Singaporean Asians) were found to be significant independent predictors. The odds ratio of dengue seroprevalence increased by 4.13 (95% CI: 2.88-5.93) for every 10 year increase in age. Dengue infections remain a major problem in Singapore.

Adolescent↗
PubMed1991

Infectious RNA transcribed from stably cloned full-length cDNA of dengue type 4 virus.

Dengue virus is an enveloped positive-strand RNA virus with a genome approximately 11 kilobases in length. The four serotypes of dengue virus are currently the most important members of the flavivirus family in terms of geographical distribution and the incidence of infection in humans. In this communication we describe successful cloning of a stable full-length cDNA copy of dengue type 4 virus that can be used as the template for in vitro transcription of infectious RNA. Evidence is presented that dengue virus recovered from permissive cells transfected with the in vitro RNA transcripts retained a mutation that was engineered into full-length cDNA. The properties of the virus produced by cells transfected with infectious RNA transcripts of dengue cDNA resembled those of the virus from which the cDNA clone was derived. The dengue virus recombinant DNA system should prove helpful in gaining a better understanding of the molecular biology of dengue viruses and should facilitate the development of a safe and effective live vaccine for use in humans.

Base Sequence↗
PubMed1977

Dengue viruses and mononuclear phagocytes. I. Infection enhancement by non-neutralizing antibody.

Cultured mononuclear peripheral blood leukocytes (PBL) from nonimmune human beings and monkeys are nonpermissive to dengue 2 virus (D2V) infection at multiplicities of infection of 0.001-0.1, but become permissive when non-neutralizing dengue antibody is added to medium. D2V infection occurred in PBL prepared from anti-coagulated but not from defibrinated plasma. Infection enhancement was produced by multiple lots of heterotypic anti-dengue raised in several mammalian species. Homotypic anti-dengue neutralized D2V at high concentrations but enhanced at low concentrations; enhancement end point in one serum was 1:320,000. The infection-enhancing factor was a noncytophilic antibody of the IgG class. D2V infection occurred in the absence of heat-labile complement components but did not occur when complexes were prepared with anti- dengue F(ab)(2). Treatment of PBL with several proteases increased permissiveness to D2V infection by immune complexes but not by virus alone. Two rhesus monkey serums collected 14 days after D2V infection contained an IgG antibody with high-titered enhancing activity but with no hemagglutination-inhibition or neutralizing activity. Virus-antibody complexes are irreversibly attached to PBL within 15 min and completely internalized in 60 min. There was considerable variation in cellular infection in different experiments, however, maximum virus yields usually exceeded 1,000 plaque-forming units per 1 x 10(6) PBL occurring between 2 and 4 days in culture. In vitro antibody-dependent infection of PBL provides a possible model for study of pathogenetic mechanisms in infants with dengue shock syndrome who passively acquire maternal anti-dengue IgG.

Animals↗
PubMed1997

Vertical transmission of dengue.

Dengue, an important mosquito-borne flavivirus infection, is endemic in Southeast Asia. We describe two mothers who had acute dengue 4 and 8 days before the births of their infants. One mother had worsening of her proteinuric pregnancy-induced hypertension, liver dysfunction, and coagulopathy and required multiple transfusions of whole blood, platelets, and fresh frozen plasma. Her male infant was ill at birth, developed respiratory distress and a large uncontrollable left intracerebral hemorrhage, and died of multiorgan failure on day 6 of life. Dengue virus type 2 was isolated from the infant's blood, and IgM antibody specific to dengue virus was detected in the mother's blood. The second mother had a milder clinical course; she gave birth to a female infant who was thrombocytopenic at birth and had an uneventful hospitalization. Dengue virus type 2 was recovered from the mother's blood, and IgM antibody specific to dengue virus was detected in the infant's blood. This report highlights not only the apparently rare occurrence of vertical transmission of dengue virus in humans but also the potential risk of death for infected neonates.

Acute Disease↗
PubMed2005

Production and characterization of a monoclonal antibody specific for NS3 protease and the ATPase region of Dengue-2 virus.

Dengue is considered a reemerging disease of worldwide distribution. The Dengue virus non-structural protein 3 (NS3) is known to possess ATPase, helicase, and protease activities that are a constitutive part of the replication complex of Dengue virus. In this report, we discuss the cloning, expressing, and purifying of the Dengue-2 NS3 protein, to immunize mice and then generate monoclonal antibodies (MAbs). Our results show the production of MAbs specific to NS3 protein of Dengue-2 virus, which by immunofluorescence recognize the native protein in experimentally infected endothelial cells (HMEC). Likewise, C6/36-infected lisates were used in Western blots, and observed the specific characteristic band that defines the NS3 protein. We conclude that these antibodies may be a useful tool, not only to study the replicative process of Dengue virus, but also to generate specific diagnostic tools for Dengue infection.

Adenosine Triphosphatases↗
PubMed2006

Elevated soluble thrombomodulin in the febrile stage related to patients at risk for dengue shock syndrome.

BACKGROUND: Children with dengue hemorrhagic fever (DHF) are at risk to develop dengue shock syndrome (DSS) for which neither marker has been demonstrated. OBJECTIVE: The study was designed to investigate the markers of vascular endothelial cell injuries and dysfunction that might be used as early predictors of the subsequent manifestation of DSS. METHODS: The blood samples from 111 patients with dengue fever, DHF and other febrile illness (OFI) were collected daily from the day of admission until discharge and at convalescent stage. The sample from the day of defervescence was defined as day 0, 1 day before defervescence was defined as day -1 and so on. Also, 1 day after defervescence was defined as day +1 and so on. RESULTS: Increased soluble thrombomodulin (sTM) was demonstrated in dengue-infected patients via an enzyme-linked immunosorbent assay. Patients with DSS (DHF grades III and IV) had higher concentrations of sTM than those with dengue fever, DHF grade I, II and OFIs from day -3 until day +2. Increased circulating endothelial cells were detected from day 0 until day +2 in DSS patients as compared with other groups. In addition, increased soluble vascular cell adhesion molecule-1, soluble intercellular adhesion molecule-1 and soluble E-selectin were also found in dengue virus-infected patients as compared with OFIs. CONCLUSION: Blood sTM may be useful as an early predictor of DSS in dengue infected patients in the febrile stage. However, a further evaluation in a large prospective series is needed.

Adolescent↗
PubMed1992

Nuclear localization of dengue 2 virus core protein detected with monoclonal antibodies.

Anti-dengue 2 virus core protein monoclonal antibodies (MAbs) reacted with antigens in the cytoplasm and in, or on, the nucleus of dengue 2 and dengue 4, but not dengue 1, dengue 3, Kunjin or Murray Valley encephalitis virus-infected cells. These MAbs also reacted with the core protein from dengue 1, 2 and 4 virions in Western blots. The antigens detected by these MAbs could not be detected in uninfected or heat-shocked cells, but were first detected in infected cells approximately 32 h post-infection. PEPSCAN epitope mapping suggested that all the MAbs react with a region of the dengue 2 virus core protein (9RNTPFNMLKRE19) which is adjacent to a putative nuclear localization sequence (6KKAR9) and spans a possible second site for the initiation of synthesis of core protein (12PFN decreases MLKR18).

Amino Acid Sequence↗
PubMed1993

Detection of dengue virus antigens in cultured cells by using protein A-gold-silver staining (pAgs) method.

A protein A-gold-silver (pAgs) staining was developed to detect dengue virus antigens in cultured cells. The method can be carried out in either newly-subcultured or monolayered cells. Dengue virus-inoculated C6/36 clone of Aedes albopictus cells and human endothelial cells appeared brown-yellowish color on the peripheral membrane of the infected cells. In many cases, the infected C6/36 cells appeared darker than that of the infected endothelial cells. The positive results from the inoculated C6/36 cells usually appeared as early as 2 days post-inoculation for types 1, 2, and 4 of dengue viruses and 3 days for the dengue 3 virus. The same batch of specimens detected by direct immunofluorescence antibody test (DFA) showed positive 4 days post-inoculation for the types 2, 3, and 4 of dengue viruses and 6 days for the dengue 1 virus. The result also showed that all pAgs-positive specimens were also DFA-positive, but not vice versa. It suggested that pAgs is not only sensitive but also specific for dengue virus detection from inoculated cultured cells.

Aedes↗
PubMed1998

Evaluation of a commercial capture enzyme-linked immunosorbent assay for detection of immunoglobulin M and G antibodies produced during dengue infection.

A commercially available capture enzyme-linked immunosorbent assay (ELISA) for the detection of specific immunoglobulin M (IgM) and IgG antibodies produced during dengue infection (PanBio Dengue Duo) was evaluated with paired serum specimens from 176 patients. Diagnosis was based on a hemagglutination inhibition (HAI) assay, with patients having either primary dengue (n = 90), secondary dengue (n = 58), or no dengue (n = 28) infection. The combined use of IgM and IgG (sensitivity, 99%; specificity, 96%) was superior to the use of IgM alone (sensitivity, 88%; specificity, 96%) or IgG alone (sensitivity, 85%; specificity, 96%). Furthermore, with the first serum sample of the pair of serum samples, the ELISA was able to diagnose significantly more cases of dengue than the HAI assay (55% versus 14%). The results of the IgG capture ELISA gave a significant correlation with those of the HAI assay (r = 0.91; P < 0.0001), and the IgG capture ELISA could be used to distinguish between primary and secondary infection. The best distinction was observed when an IgG cutoff ratio of 3.0 was used, with 88% of primary infections and 98% of secondary infections being correctly classified. This ELISA should prove to be useful in the clinical diagnosis of dengue infection.

Antibodies, Anti-Idiotypic↗
PubMed1997

Automated type specific ELISA probe detection of amplified NS3 gene products of dengue viruses.

AIM: To apply an automated system of nucleic acid hybridisation coupled with the enzyme linked immunosorbent assay (ELISA) for the type specific detection of amplification products of dengue viruses. METHODS: Non-structural 3 (NS3) gene targets of reference strains of all four dengue and other flaviviruses, as well as dengue patient viraemic sera, were subjected to reverse transcription and polymerase chain reaction using consensus and dengue type specific primers and digoxigenin-11-dUTP label incorporation. The amplification products were detected by biotinylated type specific primers which served as ELISA capture probes bound to streptavidin coated tubes. RESULTS: Significantly high spectrophotometric absorbance readings were obtained by hybridisation of the consensus and seminested amplification products of all four dengue viruses with their respective capture probes. In contrast, extremely low absorbances were observed for consensus products of Japanese encephalitis, yellow fever, and Kunjin viruses, which served as negative controls. These ELISA data correlated well with agarose gel electrophoresis of dengue type specific amplified products of diagnostic sizes. CONCLUSIONS: The combination of in vitro amplification and antibody based detection offers rapid, type specific, high throughput, and gel-free detection of amplified products of dengue viruses.

Dengue↗
PubMed2003

Analysis of saturation binding and saturation infection for dengue serotypes 1 and 2 in liver cells.

OBJECTIVE: The liver has been increasingly recognized as a significant target organ in the pathogenesis of dengue virus infection. However, only two contradictory studies have examined the binding of the dengue virus to liver cells. This study therefore sought to investigate the binding of the dengue virus to HepG2 cells. METHODS: Radiolabeled dengue virus serotypes 1 and 2 were prepared through viral propagation in Vero cells. Increasing amounts of virus were then incubated with HepG2 cells to determine the ability of the virus to achieve saturation of binding on HepG2 cells. RESULTS: Results indicated that it was not possible to reach saturation of binding under experimentally achievable conditions. We then sought to determine whether it was possible to reach a state of saturation of infection, by using increasingly high titers of virus on a constant number of cells. Dengue serotype 1 showed no evidence of saturation of infection, even at titers of 5,000 viruses per cell. In contrast, dengue serotype 2 became saturated at levels of approximately 3,000 viruses per cell. CONCLUSIONS: These results are consistent with proposals that dengue virus binding to cells is mediated initially through a low-affinity interaction with an abundant molecule on the surface of the cell and secondly through interaction with a less commonly expressed molecule, which is required for viral internalization.

Animals↗
PubMed2006

Growth and production of the dengue virus in C6/36 cells and identification of a laminin-binding protein as a candidate serotype 3 and 4 receptor protein.

OBJECTIVES: Although dengue is one of the most common mosquito-borne viral diseases, few studies have investigated the relationship between the dengue virus and mosquito cells, and this study sought to describe the binding and propagation of the dengue viruses in C6/36 cells. METHODS: The internalization and production of the dengue virus was assayed by standard plaque assay methodologies, while dengue virus receptor proteins were examined by a virus overlay protein-binding assay and candidate gene analysis coupled with virus inhibition studies. RESULTS: All four serotypes were internalized linearly, and de novo virus production occurred 14-19 h postinfection. Virus overlay protein-binding assay identified a band of 50 kDa for dengue serotypes 2, 3 and 4 which comigrated with a protein that reacts with antibodies directed against the human 37/67-kDa high-affinity laminin receptor. Both antibodies directed against the human 37/67-kDa high-affinity laminin receptor protein and soluble laminin inhibited the binding and internalization of serotypes 3 and 4, but not serotypes 1 and 2. CONCLUSIONS: The results suggest that multiple receptors may be used by the dengue virus to enter into insect cells, and that one of these proteins may be a laminin-binding protein.

Animals↗