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PubMed2003

Maternally transferred neutralising dengue antibodies in Thai infants: a pilot study.

In a dengue-endemic area, sera from 42 mother-infant pairs and sera collected from the infants at follow-up at the ages of 3 months (n =27), 6 months (n =34), 9 months (n =23) and 12 months (n =8) were tested for antibodies to four dengue serotypes using a plaque reduction neutralisation test (PRNT(50)), IgG ELISA and haemagglutination inhibition assay (HAI). The IgG ELISA and HAI tests were less sensitive than PRNT(50) in detecting low levels of antibodies. Levels of maternally transferred dengue neutralising antibodies in the cord sera were very high and identical to those in the mothers. Neutralising antibody prevalences in the newborns were 95% to dengue serotype 1 (DEN-1), 93% to DEN-2 and DEN-3 and 91% to DEN-4. The antibodies decreased with increasing age. At least one dengue serotype neutralising antibody persisted in the infants at ages 3, 6 and 9 months in 92%, 69% and 13%, respectively. No maternally transferred antibody was observed in 12-month-old infants. In endemic areas therefore, where most infants have maternally transferred dengue antibodies, interference with dengue vaccine is likely to be less after 12 months of age than before then.

Adolescent↗
PubMed2001

Development of Dengue virus type 2 replicons capable of prolonged expression in host cells.

BACKGROUND: As part of a program to develop a Dengue virus vaccine which avoids the deleterious effects of antibody dependent enhancement (ADE) of infection mediated by antibodies to Dengue virus structural proteins, we have begun to investigate the possibility of designing Dengue vaccines based on non-structural proteins. RESULTS: Dengue constructs which lack major structural proteins replicate intracellularly in tissue culture. These replicons are capable of prolonged expression of Dengue virus non-structural proteins for at least seven days in culture. CONCLUSIONS: Dengue virus genomes lacking major structural proteins can, like other flaviviruses, replicate intracellularly and express virus non-structural proteins with minimal toxicity to host cells. These findings pave the way for the development of dengue virus replicons as a form of live, attenuated virus vaccine.

Animals↗
PubMed2006

Clinical features and pitfalls in the laboratory diagnosis of dengue in travellers.

BACKGROUND: Several enzyme-linked immunosorbent assay (ELISA)-kits are commercially available for the rapid diagnosis of dengue infection, and have demonstrated good sensitivity and specificity in paired serum samples. In practice, however, often only one blood sample is available from febrile travellers returning from dengue endemic areas. METHODS: To evaluate the diagnostic value of positive dengue antibody-titres performed by a standard ELISA (PanBio IgM- and IgG-ELISA) in single serum samples (regarded as "probable infection"), 127 positive samples were further analyzed using envelope/membrane IgM-, and nonstructural protein 1 IgM- and IgG-ELISAs, immunofluorescence assays, and real-time reverse transcription polymerase chain reaction assays (RT-PCR). A combination of the test-results served as the diagnostic "gold standard". A total of 1,035 febrile travellers returning from dengue-endemic countries with negative dengue-serology and RT-PCR served as controls to compare clinical and haematological features. RESULTS: Overall, only 64 (positive predictive value = 50%) of the probable cases were confirmed by additional analysis and 54 (42.5%) were confirmed to be "false-positive". Rash was the only clinical feature significantly associated with confirmed dengue fever. The combination of thrombocytopenia and leucopenia was present in 40.4% of confirmed and in 6.1% of false-positive cases. Thus, the positive predictive value for the combination of positive PanBio-ELISA plus the two haematological features was 90.5%. CONCLUSION: The examination of paired serum samples is considered the most reliable serodiagnostic procedure for dengue. However, if only one blood sample is available, a single positive ELISA-result carries a high rate of false-positivity and should be confirmed using a second and more specific diagnostic technique. In the absence of further testing, platelet and white blood cell counts are helpful for the correct interpretation.

Adolescent↗
PubMed2005

Quantitative trait loci that control dengue-2 virus dissemination in the mosquito Aedes aegypti.

The mosquito Aedes aegypti is the most important vector of yellow fever and dengue fever flaviviruses. Ae. aegypti eradication campaigns have not been sustainable and there are no effective vaccines for dengue viruses. Alternative control strategies may depend upon identification of mosquito genes that condition flavivirus susceptibility and may ultimately provide clues for interrupting transmission. Quantitative trait loci affecting the ability of Ae. aegypti to develop a dengue-2 infection in the midgut have been mapped previously. Herein we report on QTL that determine whether mosquitoes with a dengue-2-infected gut can then disseminate the virus to other tissues. A strain selected for high rates of dengue-2 dissemination was crossed to a strain selected for low dissemination rates. QTL were mapped in the F(2) and again in an F(5) advanced intercross line. QTL were detected at 31 cM on chromosome I, at 32 cM on chromosome II, and between 44 and 52 cM on chromosome III. Alleles at these QTL were additive or dominant in determining rates of dengue-2 dissemination and accounted for approximately 45% of the phenotypic variance. The locations of dengue-2 midgut infection and dissemination QTL correspond to those found in earlier studies.

Aedes↗
PubMed2003

Dengue and the risk of urban yellow fever reintroduction in São Paulo State, Brazil.

OBJECTIVE: To propose a mathematical method for the estimation of the Basic Reproduction Number, R0, of urban yellow fever in a dengue-infested area. METHODS: The method is based on the assumption that, as the same vector (Aedes aegypti) causes both infections, all the quantities related to the mosquito, estimated from the initial phase of dengue epidemic, could be applied to yellow fever dynamics. It is demonstrated that R0 for yellow fever is, on average, 43% lower than that for dengue. This difference is due to the longer dengue viremia and its shorter extrinsic incubation period. RESULTS: In this study the analysis was expanded to the epidemiological situation of dengue in S o Paulo in the year 2001. The total number of dengue cases increased from 3,582 in 2000 to 51,348 in 2001. It was then calculated R0 for yellow fever for every city which have shown R0 of dengue greater than 1. It was also estimated the total number of unprotected people living in highly risky areas for urban yellow fever. CONCLUSIONS: Currently there is a great number of non-vaccinated people living in Aedes aegypti infested area in the state of São Paulo.

Aedes↗
PubMed2005

[Aedes aegypti infestation and occurrence of dengue in the city of Belo Horizonte, Brazil].

OBJECTIVE: To assess the association between the proportion of buildings positive for Aedes aegypti larvae measured by means of building infestation rate and dengue incidence rate. METHODS: Autochthonous dengue cases were selected and building infestation rates assessed in the coverage areas of health districts in the city of Belo Horizonte, Brazil, from October 1997 to May 2001. After grouping building infestation rates according to their distribution in quartiles, mean dengue incidence rates (for the month following the building infestation assessment) were compared using ANOVA. RESULTS: A weak though statistically significant correlation was observed between monthly dengue incidence and building infestation rates for the health districts (r=0.21; p=0.02) and coverage areas (r=0.14; p=0.00) in the study period. After grouping building infestation rates in quartiles, coverage areas of building infestation between 0.46% and 1.32% (second quartile) showed a mean monthly dengue incidence rate twice as high as areas of building infestation lower or equal to 0.45% (first quartile). Areas of building infestation between 1.33% and 2.76% (third quartile) and equal to or higher than 2.77% had a mean monthly dengue incidence rate five and seven times, respectively, higher than those areas showing 0.45% or less. CONCLUSIONS: Despite the well-known limitations of building infestation rates for estimating vector infestation and prediction of dengue epidemics, the study results indicate that higher building infestation rates were associated to a higher risk of disease transmission in the health districts and coverage areas of Belo Horizonte.

Aedes↗
PubMed2000

Dengue situation in Brazil by year 2000.

Dengue virus types 1 and 2 have been isolated in Brazil by the Department of Virology, Instituto Oswaldo Cruz, in 1986 and 1990 respectively, after many decades of absence. A successful continental Aedes aegypti control program in the Americas, has been able to eradicate the vector in most countries in the 60's, but the program could not be sustained along the years. Dengue viruses were reintroduced in the American region and the infection became endemic in Brazil, like in most Central and South American countries and in the Caribbean region, due to the weaning of the vector control programs in these countries. High demographic densities and poor housing conditions in large urban communities, made the ideal conditions for vector spreading. All four dengue types are circulating in the continent and there is a high risk of the introduction in the country of the other two dengue types in Brazil, with the development of large epidemics. After the Cuban episode in 1981, when by the first time a large epidemic of dengue hemorrhagic fever and dengue shock syndrome have been described in the Americas, both clinical presentations are observed, specially in the countries like Brazil, with circulation of more than one dengue virus type. A tetravalent potent vaccine seems to be the only possible way to control the disease in the future, besides rapid clinical and laboratory diagnosis, in order to offer supportive treatment to the more severe clinical infections.

Brazil↗
PubMed2002

Platelet adhesion to dengue-2 virus-infected endothelial cells.

Platelets in circulation normally do not adhere to resting endothelial cells. However, in response to vascular injury they adhere to stimulated endothelium and thereby play an essential role in hemostasis and thrombosis. Infection with dengue-2 virus can cause illness accompanied by thrombocytopenia and hemorrhage. Increased adherence of platelets to stimulated endothelial cells could contribute to the thrombocytopenia. In this study, adherence of radioisotopically labeled platelets to 1) unstimulated, 2) lipopolysaccharide (LPS)-stimulated, and 3) dengue-2 virus-infected human umbilical vein endothelial cells (HUVEC) was measured in an in vitro assay. Primary HUVEC were cultured in 96-well tissue culture plates in the presence or absence of LPS or dengue-2 virus. These cells were co-incubated with 3H-adenine-labeled fresh platelets for 30 min after which the cells were assayed for adherent platelets. Within 30 min there was maximum adherence of platelets to confluent LPS-stimulated HUVEC (36 +/- 4% over controls; P = 0.005). In comparison, there was a significant increase in adherence to dengue-2 infected HUVEC (78 +/- 7%; P < or = 0.001). Additionally, platelet adherence was visualized using fluorescent microscopy. Dengue-2 infection stimulated the HUVEC as monitored by expression of E-selectin. Platelets that adhered to dengue-2 or LPS-stimulated HUVEC were activated as visualized by dual fluorescent probes. These data demonstrate that human platelets adhere to dengue-2 virus-stimulated HUVEC and this interaction could contribute to the thrombocytopenia observed during infection.

Blood Platelets↗
PubMed2000

A novel method for the preparation of large cDNA fragments from dengue-3 RNA genome by long RT-PCR amplification.

For many years, dengue viruses were among the most difficult flaviviruses to isolate and to identify, but technical advances in the past 20 years have facilitated this process. Dengue viruses are usually recovered from specimens by the infection of mosquito-cell cultures. The virus may be passaged several times in cell cultures until a sufficient infectivity titer is attained. The viral nucleocapsid consists of capsid protein and an RNA genome. The dengue genome is a single stranded messenger (positive) sense RNA of approximately 11 kb in length. The isolation of dengue genomic RNA from various sources requires precautions to avoid RNases. RNases are released during cell disruption, and their activity must be inhibited as quickly as possible by using guanidinium thiocyanate in the presence of 2-mercaptoethanol. There has recently been a revolution in molecular biology with the development of the powerful reverse transcriptase (RT) and polymerase chain reaction (PCR) technology. Advanced studies on RT technique lead to much further improvement of the reverse transcriptase enzyme by genetic engineering. The Superscript II RNase H- RT (GIBCO BRL, USA) is genetically engineered DNA polymerase that synthesizes a complementary DNA strand from single-stranded RNA. DNA or an RNA-DNA hybrid. This enzyme is produced from a cloned M-MLV RT gene constructed by the introduction of point mutation in the RNase H active center. The selective mutations within the RNase H domain maintain full polymerase activity. This structural modification eliminates degradation of RNA molecules during the first strand cDNA synthesis. The combination of thermostable DNA polymerase with and without proofreading activity (3'-exonuclease activity), improved buffer conditions and thermal cycling profiles overcome the length limitation of PCR. On the basis of these findings, we have developed a long RT-PCR system for preparing large cDNA fragments of dengue 3 virus (H-87) by using the Superscript II RNase H- RT for reverse transcription and a mixture of Taq and Pwo DNA polymerases for PCR. Three large cDNA fragments covered the full genomic RNA from the 5'-end to the 3'-end of dengue-3 virus (H-87; 10,696 bps) could be successfully prepared as the lengths of 2.437 bps, 3,980 bps and 4,337 bps respectively. The ability of our developed long RT-PCR will bring speed and simplicity to genomic mapping and sequencing and facilitate studies in molecular genetics of dengue viruses.

Aedes↗
PubMed2002

Dengue infection: a global concern.

Dengue infection, one of the most important mosquito-borne viral diseases of humans, is now a significant problem in several tropical countries. The disease, caused by the four dengue virus serotypes, ranges from asymptomatic infection, undifferentiated fever, dengue fever (DF) to severe dengue hemorrhagic fever (DHF) with or without shock. DHF is characterized by fever, bleeding diathesis and a tendency to develop a potentially fatal shock syndrome. Hematological findings include vasculopathy, coagulopathy and thrombocytopenia as the most constant findings. During the last twenty-five years, there have been increasing reports of dengue infection with unusual manifestations, mainly with cerebral and hepatic symptoms. Laboratory diagnosis includes virus isolation, serology and detection of dengue ribonucleic acid. Successful treatment, which is mainly supportive, depends on early recognition of the disease and careful monitoring for shock. Prevention depends on control of the mosquito vector. More efforts must be made to understand the pathogenesis of DHF in order to develop a safe and effective dengue vaccine.

Combined Modality Therapy↗
PubMedDate not supplied

[Determinants of dengue transmission in Veracruz: an ecological approach to its control].

OBJECTIVE: To assess the ecological, social, and demographic factors associated with the transmission of dengue virus infection in Veracruz, Mexico, and to identify risk areas to target control measures. MATERIAL AND METHODS: This ecological study included data for 1,249 localities within the 11 Health Jurisdictions of the State of Veracruz, Mexico, for the 1995-1998 period. The following data were collected for each locality: total number of cases per year, population by sex, number of households, provision of public services, altitude, latitude, longitude, and deprivation index. RESULTS: Dengue transmission was registered in 17% of the localities in the State; 70% of the cases were concentrated in only 6% of the localities. Recurrent localities were urban centers with adequate availability of public services and low deprivation indices. Dengue transmission was detected in rural areas, but it was not common. The average number of cases differed according to the size of the locality and the number of years dengue was reported. A population threshold to maintain transmission was found. CONCLUSION: Recurrent localities concentrating 70% of dengue fever cases were identified, as well as the ecological and demographic factors associated with dengue transmission. The risk stratification approach to dengue transmission may improve control and prevention of this disease in high-risk areas.

Dengue↗
PubMedDate not supplied

[Neurological complications arising from dengue virus infection].

INTRODUCTION: Dengue is the most common of the arbovirosis that humans can suffer from. The frequency with which the central nervous system (CNS) is affected by this viral infection remains unknown, although isolated cases with neurological complications have been reported in Asia and South America. In Rio de Janeiro, Brazil, dengue virus infection has become an important public health concern. CASE REPORTS: The authors describe two cases of immune-mediated CNS involvement following classic infection by the dengue virus: one involving post-infectious disseminated acute encephalitis and the other consisting of Guillain-Barré syndrome. In both cases dengue was diagnosed using the ELISA technique, and other viral aetiologies in the cerebrospinal fluid (CSF) were excluded. A 10-year-old female, following a bout of classic dengue, presented symptoms of a diminished level of consciousness, spastic tetraparesis, cerebellar syndrome and frontal symptoms. A resonance brain scan showed areas of hypersignal in T2 sequences in the cerebral peduncle, lentiform nuclei and internal capsule on both sides of the brain, which suggested post-infectious encephalitis. The second patient, a 14-year-old male, presented an areflexive flaccid ascending tetraparesis that suggested acute polyradiculoneuritis, following a bout of classic dengue. CSF albuminocytologic dissociation was also observed. This patient's electroneuromyogram recording showed a polyradiculoneuropathy of a primarily demyelinating nature with an associated axonal component. CONCLUSIONS: The immunological mechanisms involved in the pathophysiology of this type of neurological complications after suffering from dengue may be part of the physiological response to the viral infection.

Adolescent↗
PubMed2004

Incomplete surveillance of a dengue-2 epidemic in Ibagué, Colombia, 1995-1997.

From April 1995 through November 1997 a dengue epidemic occurred in Ibagué (400,000 population), Colombia, where 3,419 cases were reported and DEN 2 virus was isolated from seven patients. A sero-survey conducted in 1996 found evidence of previous dengue infection in 9.6% of the population, indicating that many infections had not been reported. The dengue infections occurred in all age groups, but children under five years of age were most frequently infected. Forty-five percent of this Ibagué population were born after the re-appearance of dengue in Colombia in 1972, but have never been infected with dengue virus. Most of the cases reported as dengue hemorrhagic fever did not fulfill the current case definition. Aedes aegypti larvae were found in 19% of dwellings surveyed, most often in uncovered low tanks used for water storage. Many residents were not acquainted with the domestic nature of the mosquito vector. Health workers attributed the failure of the dengue control programs to lack of leadership and other administrative problems.

Adolescent↗
PubMed2005

Early detection of dengue infections using cluster sampling around index cases.

A two-year study using a cluster investigation method was conducted in West Jakarta, Indonesia to demonstrate the detection of dengue cases prior to onset of clinical illness. The clusters consisted of family members and neighbors of 53 hospitalized dengue index cases. Among 785 adult and child volunteers enrolled, 17 (2.2%) post-enrollment dengue (PED) infections were identified. Eight PED cases were asymptomatic and nine were symptomatic. Symptomatic cases included eight with dengue fever and one with dengue hemorrhagic fever (DHF) (grade II). Among the eight asymptomatic PED cases, viremia was detected in two. Eleven volunteers had acute dengue infections at the time of enrollment. Four of the 11 developed DHF, resulting in a total of five DHF cases detected during the investigation. This study design can serve as a benchmark for future investigations that seek to define early immunologic events following dengue infections that contribute to the development of DHF.

Adolescent↗
PubMed2005

Differences in dengue severity in infants, children, and adults in a 3-year hospital-based study in Nicaragua.

To investigate age-related differences in dengue severity, 114 infants, 1,211 children, and 346 adults with laboratory-confirmed dengue virus (DEN) infections presenting to three hospitals in major urban centers in Nicaragua were recruited from 1999 to 2001. The age distribution of dengue cases and the circulating serotype (predominantly DEN2) were representative of national data. Similar results were obtained when either dengue hemorrhagic fever/dengue shock syndrome or its principal manifestations (vascular permeability, internal hemorrhage, marked thrombocytopenia, and/or shock) were analyzed in relation to age and immune status. The burden of disease and of severe dengue was found predominantly in infants 4-9 months of age and in children 5-9 years old, and secondary DEN infection was a risk factor for severity in children. Age-related differences were identified in the prevalence of specific clinical manifestations as well as in their association with a confirmed DEN diagnosis. This represents one of the few comprehensive studies to analyze characteristics of dengue in infants, children, and adults in the same population and highlights age-related differences in dengue severity.

Adolescent↗
PubMedDate not supplied

Impact of a short-term community-based cleanliness campaign on the sources of dengue vectors: an entomological and human behavior study.

In June 2002, a considerable number of cases of dengue fever/dengue hemorrhage fever were reported in South Taiwan. To effectively reduce the sources of dengue vectors, the government conducted a weeklong community-based cleanliness campaign. The study reported here was designed to evaluate the effectiveness of the campaign. The sources of dengue vectors were evaluated according to changes in the ovitrap index. This index significantly decreased from 66.7 percent before the campaign to 39.3 percent three months later. Human knowledge and behavior were investigated by a survey questionnaire. Although the respondents had sufficient knowledge about dengue as well as its transmission and prevention, only 57.4 percent knew that the dengue vector breeds in clean water. After the campaign, this percentage significantly increased, to 88.4 percent, and the percentage of those properly handling artificial containers also significantly increased. On the basis of these findings, the authors conclude that short-term community-based cleanliness educational programs may change behavior to eliminate container habitats of the dengue vectors and in turn reduce the ovitrap index. This control strategy is a feasible alternative to rapidly reduce sources of dengue vector in urban areas, especially at the onset of a new epidemic.

Adult↗
PubMed2006

Repeated tourniquet testing as a diagnostic tool in dengue infection.

Prospective evaluation of repeated standard tourniquet testing as a diagnostic indicator of dengue infection was done. Included were patients admitted to a children's hospital in Kuala Lumpur on a clinical suspicion of dengue infection based on the World Health Organization (WHO) criteria. A standard method of tourniquet was performed on 79 patients on a daily basis following admission. subjects and negative in the remaining 14 subjects. Fifty-eight subjects were serologically confirmed cases, 4 indeterminate and the remaining 17 subjects had negative serology. For diagnostic classification, 13 had dengue fever, 49 with dengue haemmorhagic fever (DHF) while 17 had non-dengue infection. The sensitivity and specificity of the tourniquet test was 82.8% and 23.5% respectively. The positive predictive value (PPV) was 78.7% while the negative predictive value (NPV) was 28.6%. In addition, the tourniquet test aided in the diagnosis of one-fifth of patients with DHF, who presented with a positive tourniquet test as the only bleeding manifestation. It seems that in a hospital setting, the tourniquet test adds little to the diagnosis of dengue infection/DHF. A positive tourniquet test, repeatedly performed, was found clinically useful as a preliminary screening test in dengue infection as recommended by WHO. However, it was not very specific and had a high false positive rate.

Capillaries↗
PubMed2006

An evidence of intestinal mucosal injury in dengue infection.

The aim of this study was to determine whether there is an association between dengue infection and intestinal mucosal injury. Serum levels of intestinal fatty acid binding protein (I-FABP) were used as a specific marker for mucosal injury. The diagnosis of all patients was serologically confirmed by anti-dengue IgG or IgM. Serum I-FABP levels of 120 patients were determined and compared to those of 25 controls using ELISA. In order to investigate serum I-FABP among dengue patients, they were categorized into 5 groups according to disease severity: dengue fever (DF), dengue hemorrhagic fever (DHF) grade I through DHF grade IV. The dengue patients had higher levels of serum I-FABP compared to 25 controls (408.0 +/- 499.3 vs 124.72 +/- 147.81 pg/ml, p=0.006). The patients with DHF grade IV had the highest levels of serum I-FABP, ALT, and AST compared to the other groups. However, there were no differences in serum I-FABP, ALT, and AST levels among patients with DF, DHF grade I, grade II, and grade III. Evidence of intestinal mucosal injury in patients with dengue infection was demonstrated. Patients with DHF grade IV had high serum I-FABP levels and had associated liver injury.

Antibodies, Viral↗