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PubMed2004

Aedes aegypti in Brazil: genetically differentiated populations with high susceptibility to dengue and yellow fever viruses.

Aedes aegypti was eliminated from Brazil in 1955, but re-infested the country in the 1970s. Dengue outbreaks have occurred since 1981 and became endemic in several cities in Brazil after 1986. Urban yellow fever has not occurred since 1942, and only jungle yellow fever cases have been reported. A population genetic analysis using isoenzyme variation combined with an evaluation of susceptibility to both yellow fever and dengue 2 viruses was conducted among 23 A. aegypti samples from 13 Brazilian states. We demonstrated that experimental infection rates of A. aegypti for both dengue and yellow fever viruses (YFV) are high and heterogeneous, and samples collected in the endemic and transition areas of sylvatic yellow fever were highly susceptible to yellow fever virus. Boa Vista, a border city between Brazil and Venezuela, and Rio de Janeiro in the Southeast region are considered as the most important entry points for dengue dissemination. Considering the high densities of A. aegypti, and its high susceptibility to dengue and yellow fever viruses, the risk of dengue epidemics and yellow fever urbanization in Brazil is more real than ever.

Aedes↗
PubMed2000

Determination of tumor necrosis factor-alpha levels in dengue virus infected patients by sensitive biotin-streptavidin enzyme-linked immunosorbent assay.

A modified sandwich enzyme-linked immunosorbent assay using biotin-streptavidin system (BS-ELISA) was developed to determine levels of tumor necrosis factor-alpha (TNF-alpha) in serum samples of children infected with dengue virus (n=99) and healthy controls (n=41). The minimum detectable concentration of TNF-alpha by the BS-ELISA was 3.3 pg/ml. The mean TNF-alpha level was highest in those patients with dengue shock syndrome (DSS) or dengue hemorrhagic fever (DHF) grade III (37.44+/-42.0 pg/ml). Lower levels were found in DHF grade I (28.44+/-42.7 pg/ml), DHF grade II (24. 21+/-25.4 pg/ml) and dengue fever (DF) (14.10+/-24.0 pg/ml). TNF-alpha in the sera of DF and DHF patients could be detected on days 2-6 after the onset of fever, the high level occurring on day 5. TNF-alpha was detected in 41.4% (24.01+/-35.2 pg/ml) of dengue virus infected patients and 7.3% (4.2+/-15.6 pg/ml) of control subjects. The sera of patients contained significantly higher levels of TNF-alpha than the sera of controls, P-value<0.001. DHF patients had significantly higher levels of TNF-alpha than DF patients (P-value=0.020) but no difference in the TNF-alpha levels from sera of DHF grades I-III patients was observed (P-value=0.295). The results indicate that the BS-ELISA is a very sensitive method for determining TNF-alpha in serum samples of DF and DHF patients. The TNF-alpha levels might be associated with dengue virus infection and related to disease severity of DHF.

Adolescent↗
PubMed2001

Development of dengue IgM-capture enzyme-linked immunosorbent assay with higher sensitivity using monoclonal detection antibody.

An IgM-capture enzyme-linked immunosorbent assay (IgM-ELISA) is used widely for serodiagnosis of dengue. A dengue IgM-ELISA with higher sensitivity has been developed. In the new ELISA, anti-dengue IgM antibody, which had been captured on the solid phase, was reacted with tetravalent dengue viral antigens, and detected by a flavivirus group specific monoclonal antibody, D1-4G2-4-15 (4G2). Reaction of 4G2 to viral antigens was similar to that of dengue patients' IgG. Non-specific reaction of 4G2 to the control antigen, which was prepared from uninfected cell culture fluid of mosquito C6/36 cells, was much lower than that of patients' IgG. Thus, specificity of the ELISA with 4G2 was much higher than that with patients' IgG, and lower levels of specific IgM was detected in the serum samples. These results suggest that the modified dengue IgM-ELISA with monoclonal antibody 4G2 has many advantages over the original "in-house" ELISA.

Antibodies, Monoclonal↗
PubMed2001

Study of biologic attributes of Cuban dengue 2 virus after serial passage in primary dog kidney cells.

OBJECTIVE: The serial passage of dengue viruses in primary dog kidney (PDK) cells has resulted in selection of attenuated viruses. However, the molecular changes responsible for loss of virulence are not well characterized. This article describes the isolation and biologic attributes of one dengue 2 virulent strain as a first step to allow the study of determinants of virulence at the molecular level. METHODS: A15 dengue 2 Cuban strain was isolated from the viremic plasma of a patient with uncomplicated dengue fever during the 1981 epidemic. This was then subjected to serial passage in PDK cells. Viruses resulting from several PDK passages were compared to the parent strain for plaque size and temperature sensitivity, neurovirulence in newborn mice, and cytopathogenic effects on LLC-MK(2) and C6/36-HT cell lines. RESULTS: A15 dengue 2 Cuban strain was successfully propagated in PDK cells. Primary dog kidney 52 to 53 viruses exhibited several biologic attributes, such as small plaques, temperature sensitivity, reduced mouse neurovirulence, and cytopathic effect in permissive cell lines. CONCLUSIONS: These results represent the first step to allow attenuation of this strain of dengue 2 virus.

Animals↗
PubMed1999

Evaluation of an IgG enzyme-linked immunosorbent assay for dengue diagnosis.

BACKGROUND: The hemagglutination inhibition (HI) test has been one of the standards, with the IgM antibody capture ELISA (MAC-ELISA), for the diagnosis of dengue virus infections. The spread of dengue throughout the world and the increasing number of cases to be tested makes an ELISA-format test for IgG antibodies to replace the HI test highly desirable. OBJECTIVES: Evaluate the use of the IgG-ELISA as a substitute for the HI test in dengue diagnosis. STUDY DESIGN: Paired serum samples defined as being from primary or secondary dengue virus infections by HI, were tested by an ELISA that detects IgG antibodies. The correlations of titers and serologic interpretations between these two tests were examined. RESULTS: The IgG-ELISA showed a low correlation with the HI in primary infections, and a higher correlation in secondary infections because of the influence of IgM antibodies in the HI test. Nevertheless, IgG ELISA titers could be reliably associated with primary or secondary infections when analyzed by days after onset of symptoms, and can be used to characterize the immune response after flavivirus infections. CONCLUSION: The combination of the IgM and IgG ELISAs may be used to serologically diagnose dengue virus infections, since the IgG ELISA can substitute for the HI test in characterizing the immune response to dengue virus infections.

Antibodies, Viral↗
PubMed2005

Dengue virus-associated hemophagocytic syndrome and dyserythropoiesis: a case report.

A 33-year-old man had dengue hemorrhagic fever with initial presentation of fever, leukocytosis, and thrombocytopenia. The cause of the subsequent rapid decline in red cell counts without evidence of intravascular hemolysis or massive bleeding was confirmed as hemophagocytosis and dyserythropoiesis by bone marrow study. The patient recovered with supportive care and the bone marrow pattern was normal on repeated bone marrow study. To our knowledge, this is the first reported case of dengue virus-associated hemophagocytosis and dyserythropoiesis in Taiwan. Clinicians should consider that the occurrence of hemophagocytosis and dyserythropoiesis could be due to dengue virus infection. That this dengue virus infection was confirmed by a positive serology result at the convalescent stage but not at the acute symptomatic stage underlines the need for a second dengue serology study, as dengue infection can be missed due to an initial negative serology result.

Adult↗
PubMed2003

Original antigenic sin and apoptosis in the pathogenesis of dengue hemorrhagic fever.

Dengue virus presents a growing threat to public health in the developing world. Four major serotypes of dengue virus have been characterized, and epidemiological evidence shows that dengue hemorrhagic fever (DHF), the more serious manifestation of the disease, occurs more frequently upon reinfection with a second serotype. We have studied dengue virus-specific T-cell responses in Thai children. During acute infection, few dengue-responsive CD8+ T cells were recovered; most of those present showed an activated phenotype and were undergoing programmed cell death. Many dengue-specific T cells were of low affinity for the infecting virus and showed higher affinity for other, probably previously encountered strains. Profound T-cell activation and death may contribute to the systemic disturbances leading to DHF, and original antigenic sin in the T-cell responses may suppress or delay viral elimination, leading to higher viral loads and increased immunopathology.

Apoptosis↗
PubMed1998

Short communication: dengue serotype 2 subtype III ('Jamaica') epidemic in Santa Cruz, Bolivia.

BACKGROUND: During the past decade, dengue and dengue haemorrhagic fever (DHF) have become a public health problem in various Latin American countries. Indications of increased dengue cases in the city of Santa Cruz, Bolivia, early in 1997 were promptly investigated. METHODS: We conducted a sample sero-survey in one district of the city. Levels of antidengue IgM were determined and genetic analysis was performed on virus isolates. RESULTS: IgM antibodies were detected in 6.5% (95% CI: 3.4%-9.6%) of adults (over 15 years old) and 5.1% (2.0%-8.2%) of children (5-7 years old). Dengue virus serotype 2 subtype III ('Jamaica') was isolated. CONCLUSIONS: The estimated attack rates are compatible with a dengue epidemic in Santa Cruz. Isolation of dengue-2 'Jamaica' virus documents the further spread of this subtype from the Caribbean via Brazil into South America. Increased DHF preparedness seems mandatory.

Adult↗
PubMed2002

Dengue virus infection rate in field populations of female Aedes aegypti and Aedes albopictus in Singapore.

We developed a single-step reverse transcription-polymerase chain reaction (RT-PCR) followed by a semi-nested PCR using an upstream consensus primer and four type-specific primers within the non-structural protein gene (NS3) of dengue viruses to type dengue viruses in field populations of female Aedes mosquitoes. This yielded diagnostic fragments of 169, 362, 265 and 426 base pairs for dengue virus types 1, 2, 3 and 4, respectively. From 1997 to 2000, 54 (6.9%) of 781 Aedes aegypti and 67 (2.9%) of 2256 Aedes albopictus screened were positive for dengue viruses, with a declining trend. The most common dengue virus type detected in the Aedes mosquitoes was dengue-1. Details on the change of one serotype to another in the mosquito population over three consecutive years are discussed.

Aedes↗
PubMed2003

Clinical and laboratory features of dengue virus-infected travellers previously vaccinated against yellow fever.

Dengue is a mosquito-borne viral infection endemic throughout the tropics and subtropics. The global prevalence of dengue has grown dramatically in recent years and it has become a major international public health concern. The close taxonomic relationships between yellow fever and dengue viruses gave rise to concerns that previous vaccination against yellow fever could modify the course of dengue infection and contribute to the development of dengue haemorrhagic fever/dengue shock syndrome (DHF/DSS). This study reports the clinical and laboratory features of dengue virus-infected travellers previously vaccinated against yellow fever.

Adult↗
PubMed1987

Induction of interferon alpha from human lymphocytes by autologous, dengue virus-infected monocytes.

Human monocytes actively replicate dengue virus. To dissect the primary immune responses to dengue virus-infected monocytes (DV-monocytes), we analyzed the interaction between autologous DV-monocytes and the peripheral blood lymphocytes (PBL) of dengue nonimmune donors. Interferon (IFN) activity was detected when PBL were cultured with DV-monocytes. Cell contact between PBL and DV-monocytes was required for IFN production; however, MHC compatibility between PBL and monocytes was not necessary. DV-monocytes fixed with paraformaldehyde or glutaraldehyde, which produced no infectious virus, also induced high levels of IFN from PBL. The ability of DV-monocytes to induce IFN correlated with the appearance of dengue antigens. The PBL that produce IFN were characterized by FACS sorting using monoclonal and polyclonal antibodies. HLA-DR+ and T3- cells produced high titers of IFN, while HLA-DR- and T3+ cells produced very low or undetectable levels of IFN. Moderate titers of IFN were produced by cells contained in B cell fractions (surface immunoglobulin-positive, B1+, and Leu-12+), and cells contained in natural killer cell fractions (Leu-11+ and OKM1+). Therefore, IFN-producing cells are heterogeneous, and the predominant producer cells are characterized as HLA-DR+ and non-T lymphocytes. The IFN produced was characterized by RIA using mAbs to IFN-alpha and IFN-gamma. The IFN-alpha was the predominant IFN produced; in addition, a low level of IFN-gamma was also detected in some experiments. The culture fluids obtained from PBL exposed to autologous DV-monocytes, which contained high IFN activity, completely inhibited dengue virus infection of monocytes. These results suggest that IFN-alpha produced by PBL exposed to DV-monocytes may play an important role in controlling primary dengue virus infection.

Antibodies, Monoclonal↗
PubMed2000

Dengue viremia titer, antibody response pattern, and virus serotype correlate with disease severity.

Viremia titers in serial plasma samples from 168 children with acute dengue virus infection who were enrolled in a prospective study at 2 hospitals in Thailand were examined to determine the role of virus load in the pathogenesis of dengue hemorrhagic fever (DHF). The infecting virus serotype was identified for 165 patients (DEN-1, 46 patients; DEN-2, 47 patients; DEN-3, 47 patients, DEN-4, 25 patients). Patients with DEN-2 infections experienced more severe disease than those infected with other serotypes. Eighty-one percent of patients experienced a secondary dengue virus infection that was associated with more severe disease. Viremia titers were determined for 41 DEN-1 and 46 DEN-2 patients. Higher peak titers were associated with increased disease severity for the 31 patients with a peak titer identified (mean titer of 107.6 for those with dengue fever vs. 108.5 for patients with DHF, P=.01). Increased dengue disease severity correlated with high viremia titer, secondary dengue virus infection, and DEN-2 virus type.

Adolescent↗
PubMed2001

Strong HLA class I--restricted T cell responses in dengue hemorrhagic fever: a double-edged sword?

Dengue is an increasingly important cause of morbidity and mortality in the tropics, but vaccine development has been impeded by a poor understanding of disease pathogenesis and, in particular, of immunologic enhancement. In a large case-control study of Vietnamese patients with dengue hemorrhagic fever (DHF), variation at the HLA-A locus was significantly associated with susceptibility to DHF (P=.02), and specific HLA-A susceptibility and resistance alleles were identified. HLA-A-specific epitopes were predicted from binding motifs, and ELISPOT analyses of patients with DHF revealed high frequencies of circulating CD8 T lymphocytes that recognized both serotype-specific and -cross-reactive dengue virus epitopes. Thus, strong CD8 T cell responses are induced by natural dengue virus infection, and HLA class I genetic variation is a risk factor for DHF. These genetic and immunologic data support both protective and pathogenic roles for dengue virus-specific CD8 T cell responses in severe disease. The potentially pathogenic role of serotype-cross-reactive CD8 T cells poses yet another obstacle to successful dengue vaccine development.

Adolescent↗
PubMed1997

Dengue virus inhibits human hematopoietic progenitor growth in vitro.

Dengue disease, whether it be classical dengue fever (DF), dengue hemorrhagic fever (DHF), or dengue shock syndrome (DSS), is frequently associated with hematologic disorders. The underlying cause of these abnormalities is unknown. To determine if an inhibitory effect on human hematopoietic progenitor growth can be observed, normal cord blood mononuclear cells were exposed to low-passaged clinical isolates from DF, DHF, and DSS patients and to the prototype strain of dengue-3 virus (H-87). In primary methylcellulose cultures, there was no inhibition of colony formation. After an initial 8-day liquid culture, inhibition was observed with the isolates, but strain H-87 had no effect. Furthermore, isolates from patients with DSS showed a more potent inhibitory effect. These data represent the first documented study of in vitro impaired progenitor cell growth by dengue virus and suggest that this inhibition could be dependent upon the isolate tested.

Antigens, Viral↗
PubMed2006

Ethnicity and difference in dengue virus-specific memory T cell responses in Cuban individuals.

The different risk factors associated with dengue hemorrhagic fever pathogenesis needs yet additional clarification. The exceptional epidemiological circumstances in Cuba allow their evaluation in a well-defined situation. In the present study the memory T cell response of 80 Cuban donors previously infected with dengue-1 and dengue-2 during the 1977 and 1981 epidemics, and belonging to different ethnic groups, was examined. White people showed, in contrast to black people, stronger and remarkably cross-reactive dengue virus-specific memory CD4(+) T lymphocyte proliferation and interferon-gamma release. The observed variation in T cell response according to ethnicity could be related to the immunopathogenesis of dengue hemorrhagic fever, and may partially explain the epidemiological evidence that black individuals are at lower risk for the most severe dengue clinical course compared with white individuals.

Adult↗
PubMedDate not supplied

The reemergence of dengue in China.

In 1978, dengue was reported in China for the first time in 32 years. Since then, epidemics involving hundreds of thousands of people have occurred in Guangdong and Guangxi provinces and on Hainan Island. These epidemics were caused by all four types of dengue virus. Aedes aegypti was the vector in coastal areas, while Aedes albopictus was the vector in inland regions. During these epidemics, case rates were very high (greater than 50%) in some areas. Case-fatality rates were generally less than 0.1% except during the 1986 outbreak on Hainan Island, when the rate was 0.25%. Hemorrhagic disease occurred in both children and adults. On Hainan Island, hemorrhagic disease was more than three times as common in the 1986 outbreak as in the 1980 outbreak; the 1980 outbreak was caused by dengue virus type 3 and the 1986 outbreak by dengue virus type 2. The weight of the evidence suggests that the reemergence of dengue in China resulted from the introduction of the infection by travelers and refugees from areas of Asia where dengue is endemic.

Aedes↗
PubMed1994

Production of interleukin-1 (IL-1) and IL-1 inhibitor by human monocytes exposed to dengue virus.

Dengue hemorrhagic fever-dengue shock syndrome, the most severe manifestation of an acute dengue virus (DV) infection, is endemic in Southeast Asia. Antibody-dependent enhancement of DV growth in mononuclear phagocytes is thought to be the mechanism whereby preexisting dengue antibodies confer excess risk for this outcome. Interleukin-1 (IL-1) may play an important role in the pathogenetic mechanisms that cause dengue fever and shock. It was shown that both IL-1 and tumor necrosis factor-alpha are secreted from monocytes within 4 h after DV infection. However, there was no increase in IL-1 secretion by virus-stimulated monocytes from dengue fever patients compared with healthy controls. Significant amounts of IL-1 were secreted by DV-infected monocytes in the presence of aggregated immunoglobulin or immune complexes. In addition, a new 600-kDa IL-1 inhibitor from the supernatants of DV-infected monocytes was identified. This inhibitor may cause immunosuppression and influence the process of DV infection.

Asia, Southeastern↗
PubMed2004

Safety and immunogenicity of a three dose regimen of two tetravalent live-attenuated dengue vaccines in five- to twelve-year-old Thai children.

OBJECTIVE: The safety and immunogenicity of tetravalent live-attenuated dengue vaccines after a three dose vaccination series were evaluated in Thai children. METHOD: One hundred three healthy flavivirus-seronegative schoolchildren ages 5 to 12 years were randomized to receive either dengue vaccine containing 3, 2, 1 and 2 log10 of the 50% cell culture infective dose, respectively, of the live-attenuated dengue vaccine serotypes 1, 2, 3 and 4 per dose (F3212; n = 40) or 3, 3, 1 and 3 log10 of the 50% cell culture infective dose (F3313; n = 42) or purified Vero cell rabies vaccine (control group; n = 21) given in a two dose schedule (3 to 5 months apart). A third dose was administered 8 to 12 months after the second dose to 90 subjects. Safety and immunogenicity were evaluated within 28 days after each injection. RESULTS: No serious adverse event related to the vaccines occurred. Most children experienced mild to moderate fever, rash, headache and myalgia occurring within 12 days after Dose 1 and generally lasting 3 days or less. One subject in Group F3212 had a 1-week dengue-like fever. Reactogenicity was minimal after Doses 2 and 3. Transient mild variations in liver enzymes and hematologic indices were noted mainly after Dose 1. After the third dose 89% of the subjects in Group F3212 seroconverted (neutralizing antibody response, > or =10) to all four serotypes, and all children in Group F3313 seroconverted. CONCLUSION: This study demonstrates a moderate although improvable reactogenicity and high seroconversion rates against the four serotypes of dengue after a three dose schedule of tetravalent live-attenuated dengue vaccine in children.

Antibodies, Viral↗