Incidence and risk factors of probable dengue virus infection among Dutch travellers to Asia

We studied the incidence of dengue virus (DEN) infections in a cohort of Dutch short-term travellers to endemic areas in Asia during 1991-92. Sera were collected before and after travel. All post-travel sera were tested for DEN immunoglobulin M (IgM) [IgM capture (MAC)-enzyme-linked immunosorbent assay (ELISA)] and IgG (indirect ELISA). Probable DEN infection was defined as IgM seroconversion or a fourfold rise in IgG ratio in the absence of cross-reaction with antibody to Japanese encephalitis virus (JEV). Infections were considered clinically apparent in case of febrile illness (> 24 H) with headache, myalgia, arthralgia or rash. Probable DEN infection was found in 13 of 447 travellers (incidence rate 30/1000 person-months, 95% CI 17.4-51.6). One infection was considered secondary; no haemorrhagic fever occurred. The clinical-to-subclinical infection rate was 1 : 3.3. The risk of infection showed marked seasonal variation. DEN infections are frequent in travellers to endemic areas in Asia; most remain subclinical.     

Original antigenic sin in dengue

Sequential blood samples were obtained from eight Thai children before, during and 3-5 months after hospitalization for dengue shock syndrome. All patients experienced a secondary-type antibody response as evidenced by hemagglutination-inhibition antibody responses in acute and convalescent sera. Dengue 2 viruses were recovered from two patients. In their pre-illness blood sample, all children had monotypic neutralizing antibodies; five to dengue 1, two to dengue 3 and one to dengue 4. The highest neutralizing antibody titers in acute phase and late convalescent sera were to the initial infecting virus type. This report documents for sequential dengue infections the existence of an original antigenic sin antibody response. It may be possible to apply this phenomenon to identify initial dengue serotype infection in individuals experiencing secondary dengue infections, thus helping to clarify the antecedents to dengue shock syndrome.     

Incidence of Dengue Virus Infection in School-Aged Children in Puerto Rico: A Prospective Seroepidemiologic Study

Dengue is a potentially fatal acute febrile illness caused by the mosquito-borne dengue viruses (DENV-1 to -4). To estimate DENV seroincidence in school-aged children, a 1-year prospective cohort study was conducted in Patillas, Puerto Rico; 10- to 18-year-olds (N = 345) were randomly selected from 13 public schools. At enrollment, 49.8% of the entire cohort had DENV immunoglobulin G (IgG) anti-DENV antibodies, and there were individuals with neutralizing antibodies specific to each of the four DENV. The mean age of participants with incident DENV infection was 13.4 years. The 1-year seroincidence rate was 5.6%, and 61.1% of infections were inapparent. Having IgG anti-DENV at enrollment was associated with seroincidence (risk ratio = 6.8). Acute febrile illnesses during the study period were captured by a fever diary and an enhanced and passive surveillance system in the municipios of Patillas and Guayama. In summary, at enrollment, nearly one-half of the participants had a prior DENV infection, with the highest incidence in the 10- to 11-year-olds, of which most were inapparent infections, and symptomatic infections were considered mild.     

Dengue fever in American military personnel in the Philippines: clinical observations on hospitalized patients during a 1984 epidemic

From June - August, 1984, 24 American military personnel were hospitalized with dengue (DEN) at Clark Air Base in the Philippines. Their infections were confirmed by serology using the hemagglutination-inhibition test and/or by virus isolation in Aedes pseudoscutellaris cell cultures. Most of the patients had a secondary type of antibody response probably reflecting prior vaccination against yellow fever. Three serotypes of DEN virus were isolated; 7 isolates of DEN 1, 4 isolates of DEN 3 and 3 isolates of DEN 2. All of the patients were Caucasian males between the ages of 20-43 years. All of the cases were clinically diagnosed as classical dengue fever. A platelet count of less than or equal to 100,000/microliters was a common finding (83.3%); however, hemoconcentration was not documented. Other major findings were the occurrence of mild hypotension (62.5%) and petechiae (37.5%). One patient presented with shock and upper gastrointestinal bleeding, but his diagnosis was complicated by a history of epigastric pain and use of aspirin. Although all of the patients fully recovered, the severity of illness was clearly documented by the average-length of hospitalization (5.9 days) and average time absent from work (8.7 days).     

Fulminant liver failure secondary to haemorrhagic dengue in an international traveller.

Dengue infections are caused by a single-stranded RNA virus, which has four serotypes (DEN 1-4); mosquitoes of the genus Aedes serve as vectors of transmission. Risk factors for dengue infection are related to both the host and virus. Age, gender, immune status, and genetic background of the host all contribute to the severity of dengue infection. Recently, international travel to endemic areas has also been identified as a major risk factor for both primary and secondary dengue infection. Dengue remains a diagnostic challenge, given its protean nature, ranging from mild febrile illness to profound shock. The most severe manifestation of dengue infection is dengue shock syndrome, which has an estimated mortality rate close to 50%. Dengue shock syndrome typically presents with increased anion gap metabolic acidosis, disseminated intravascular coagulation, severe hypotension, and jaundice. Liver involvement appears to occur more frequently when infections involve DEN-3 and DEN-4 serotypes. While hepatocellular damage has been reported previously in dengue infection, acute liver failure is an extremely rare occurrence in adults. We report a patient with dengue shock syndrome who presented with acute liver failure and hepatic encephalopathy after recent travel to an endemic area.     

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.     

Relationship of preexisting dengue virus (DV) neutralizing antibody levels to viremia and severity of disease in a prospective cohort study of DV infection in Thailand

BACKGROUND: Infection with any 1 of the 4 dengue viruses (DVs) can produce several illnesses, ranging from a mild febrile illness to classic dengue fever (DF) to dengue hemorrhagic fever (DHF), a potentially life-threatening disease. Most DHF cases occur after sequential heterotypic DV infections. The role of preexisting humoral immunity in modifying severity of dengue disease is not well understood. METHODS: We conducted a prospective cohort study of children in a region where dengue disease is hyperendemic and examined the role of preexisting neutralizing anti-DV antibodies (Abs) in modifying secondary dengue-3 virus (D3V), dengue-2 virus (D2V), and dengue-1 virus (D1V) infections. RESULTS: In secondary D3V infection, higher levels of preexisting neutralizing Ab directed against D3V (reference virus strain and patient's virus isolate) were associated with lower viremia levels and milder disease. Preexisting neutralizing Ab levels against D2V were not associated with severity of secondary D2V infection. The levels of preexisting neutralizing Ab against the infecting virus isolates were not associated with viremia levels in secondary D2V or D1V infections. CONCLUSIONS: Cross-reactive memory humoral immune responses appear to be beneficial in symptomatic secondary D3V infection, but not in secondary D2V or D1V infection. These results may have important implications for the development of live attenuated tetravalent dengue vaccines.     

Clinical differences among PCR-proven dengue serotype infections

The objective of this study was to compare the clinical spectra of the dengue serotypes proven by the PCR technique. This retrospective study reviewed the clinical information of dengue-infected patients who were admitted to northeastern provincial hospitals in Thailand from June to September 2002. Dengue infection and viral serotypes were confirmed by polymerase chain reaction (PCR). Paired anti-dengue immunoglobulin G (IgG) and IgM from paired sera were analyzed by enzyme-linked immunosorbent assay (ELISA). Ninety-nine PCR-proven dengue-infected Thai patients were studied. Their ages ranged from 3-30 years. They were infected with DEN1, DEN2, DEN3 and DEN4 in 21, 55, 12, and 12%, respectively. Twenty-two percent had primary and 78% had secondary infections. Dengue fever was the most common presentation for both primary (77.2%) and secondary infections (46.7%). The ratios of dengue fever:dengue hemorrhagic fever (DF:DHF) and non-dengue shock syndrome:dengue shock syndrome (non-DSS:DSS) for DEN2 was the lowest of the dengue serotypes. There was no difference in the duration of fever, percentage of hepatomegaly and bleeding among the serotypes in both DF and DHF. The trends in the white blood cells, lymphocyte and atypical lymphocyte counts in DEN3 were the highest, while those of DEN1 were the lowest of the dengue serotypes.     

Absence of dengue 2 infection enhancement in human sera containing Japanese encephalitis antibodies

Sera from 52 young adults resident in a rural area in North Thailand were studied for plaque-reducing neutralizing antibodies against dengue (DEN) viruses types 1-4 and Japanese encephalitis (JE), and for DEN-2 infection-enhancing antibodies using a newly described microtest in the human monocyte cell line, U-937. Infection-enhancing antibody titers in U-937 cells using a simplified micromethod were similar to results obtained by published methods using human peripheral blood leukocytes and a macrotest using U-937 cells. In the sample, there were 23 with antibodies to one or more DEN viruses with or without accompanying JE antibodies; 16 sera demonstrated antibodies only to JE and 13 had no detectable antibodies to any flavivirus. All but two DEN antibody-containing sera enhanced DEN-2 infections in U-937 cells, often to titers of 1:10,000 or greater. By contrast, only one of 16 JE-immune sera enhanced DEN-2 infection in monocytes, and that at a dilution of 1:100. None of the flavivirus-negative sera had DEN-2 enhancing activity. The failure of human anti-JE contrasts with the ability of rabbit anti-JE to enhance DEN-2 infections, but correlates with the absence of recorded instances of dengue shock syndrome in human beings sequentially infected with JE and then a DEN virus. This report seemingly reconciles in vitro and in vivo phenomena, and may provide an opportunity to study mechanisms involved.     

用3'非编码区通用引物通过RT-PCR检测登革1～4型病毒RNA

目的 　根据登革病毒 (DEN) 3 端非编码区的一段高度保守序列 ,设计登革 1～ 4型通用引物 ,采用逆转录聚合酶链反应 (RT PCR)检测登革病毒 1～ 4型RNA。方法　用C6/ 3 6细胞培养登革病毒。用热酚法提取病毒RNA ,进行RT PCR扩增 ,并对扩增产物测序。结果　DEN 2 NGC株可扩增出至少 10TCID5 0 的病毒 ,测序结果与已知序列一致。DEN 1～ 4型标准株和DEN -2 -0 4与DEN 2 4 3株均能够扩增出唯一的一条特异条带。结论　应用通用引物RT PCR法可从病毒浓度少至 10TCID5 0 的感染细胞培养液中检出DEN 2 NGC株病毒 ,并且该对通用引物对于其他 3型登革病毒亦具有很好的通用性 ,其方法的特异性和敏感性亦较强。     

Introduction of the American/Asian genotype of dengue 2 virus into the Yucatan State of Mexico

A dengue (DEN) outbreak occurred in the Yucatan State of Mexico in 2002. Three isolates were obtained from patients presenting with DEN-like symptoms, and examined by partial nucleotide sequencing and phylogenetic analysis. The isolates were identified as DEN-2 viruses of the American-Asian genotype; this is the first report of this genotype in the Yucatan State. The DEN-2 viruses of the American-Asian genotype have been associated with more severe disease outcomes. Thus, its introduction into the Yucatan State presents a serious problem to public health authorities. During this outbreak, DEN virus infection was confirmed in 18% (282 of 1,560) of the patients who presented with DEN-like symptoms. Of these, 87 (31%) patients met the World Health Organization criteria for dengue hemorrhagic fever, including two patients who died. The majority (77%) of the patients experienced secondary infections in this epidemic.     

Antibody-dependent enhancement of dengue virus growth in human monocytes as a risk factor for dengue hemorrhagic fever

Serum specimens collected during a prospective study of dengue infections among schoolchildren in Bangkok were tested for their ability to enhance dengue 2 (DEN-2) virus growth in human monocytes in vitro. Two groups of dengue-immune sera were compared: 32 dengue antibody positive serum specimens from children who subsequently developed asymptomatic secondary dengue infections; and 9 dengue antibody positive serum specimens from children who subsequently developed severe symptomatic secondary dengue infections, 8 of which were clinically diagnosed as dengue hemorrhagic fever. Antibody-dependent enhancement of virus growth was quantitated by measurement of virus yields in supernatant fluids of normal human monocyte cultures that were infected with DEN-2 virus in the presence of undiluted test serum. Only 4 of 32 (12%) preinfection sera from asymptomatic children, but 6 of 9 (67%) preinfection sera from symptomatic children, had significant enhancing activity (P less than 0.001). High serum DEN-2 antibody dependent enhancing activity is a significant (relative risk = 6.2) risk factor for severe illness among children in a dengue hemorrhagic fever endemic region. Dengue antibodies can be neutralizing and therefore protective, or they can be enhancing and increase the risk of dengue hemorrhagic fever.     

Burden of Dengue Infection and Disease in a Pediatric Cohort in Urban Sri Lanka

Dengue is the most significant arthropod-borne viral infection of humans. Persons infected with dengue viruses (DENV) have subclinical or clinically apparent infections ranging from undifferentiated fever to dengue hemorrhagic fever/shock syndrome. Although recent studies estimated that the Indian subcontinent has the greatest burden of DENV infection and disease worldwide, we do not have reliable, population-based estimates of the incidence of infection and disease in this region. The goal of this study was to follow-up a cohort of 800 children living in a heavily urbanized area of Colombo, Sri Lanka to obtain accurate estimates of the incidence of DENV infection and disease. Annual blood samples were obtained from all children to estimate dengue seroprevalence at enrollment and to identify children exposed to new DENV infections during the study year. Blood was also obtained from any child in whom fever developed over the course of the study year to identify clinically apparent DENV infections. At enrollment, dengue seroprevalence was 53.07%, which indicated high transmission in this population. Over the study year, the incidence of DENV infection and disease were 8.39 (95% confidence interval = 6.56–10.53) and 3.38 (95% confidence interval = 2.24–4.88), respectively, per 100 children per year. The ratio of clinically inapparent to apparent infections was 1.48. These results will be useful for obtaining more accurate estimates of the burden of dengue in the region and for making decisions about testing and introduction of vaccines.     

Induction of bivalent immune responses by expression of dengue virus type 1 and type 2 antigens from a single complex adenoviral vector

There are approximately 100 million new cases of dengue (DEN) virus infection each year. Infection can result in illness ranging from a mild fever to hemorrhaging, shock, or even death. There are four serotypes of dengue virus (DEN1-4), and immunity to one serotype does not cross protect from infection with other serotypes. Currently there are no approved vaccines for dengue fever. In this report, we describe the construction of a bivalent dengue virus vaccine using a complex recombinant adenovirus approach to express multiple genes of DEN1 and DEN2 serotypes. In vaccinated mice, this vector induced humoral immune responses against all four dengue serotypes as measured by enzyme-linked immunosorbent assay. However, the neutralizing antibody responses were specific for DEN1 and DEN2 serotypes. Expansion of this vaccine development platform towards the DEN3 and DEN4 serotypes can lead towards the development of an adenovirus-based tetravalent dengue vaccine.     

Effect of age on outcome of secondary dengue 2 infections.

OBJECTIVE: Dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) is a growing global health problem. It is not known how age affects the outcome of secondary dengue infections. In an island setting, a large DHF/DSS outbreak in Cuba occurred in 1981. Involved were individuals, 3-40 year old, whose only lifetime dengue exposure was to DEN-1 in 1977 and DEN-2 in 1981. In this report we calculate age-specific DHF/DSS hospitalization and death rates based on secondary DEN 2 infections. METHODS: Published and unpublished hospital and seroepidemiologic data from the 1981 DHF/DSS outbreak were used for the analysis. RESULTS: Children, aged 3 and 4 years, with secondary DEN-2 infections were found to have a high death rate (25.4/10 000 secondary DEN-2 infections). The death rate fell with increasing age, being 15.9-fold lower in the 10-14-year age group. The death rate for children aged 3-14 years was 14.5-fold higher than in young adults aged 15-39 years. The death rate rose somewhat in adults aged 50 years and older. DHF/DSS hospitalization rates showed the same trend as death rates. CONCLUSIONS: Age is an important variable in the outcome of secondary DEN-2 infections. DHF/DSS case fatality and hospitalization rates are highest in young infants and the elderly. The risk that a child will die during a secondary DEN-2 infection is nearly 15-fold higher than the risk in adults.     

A prospective study of dengue infections in Bangkok

Dengue infections were prospectively studied among 4- to 16-year-old students at a Bangkok school. Blood samples were obtained from 1,757 students in June 1980, before the dengue season, and in January 1981, after the season, and tested for dengue antibodies by the hemagglutination inhibition method. Classrooms were monitored daily for school absences. Fifty percent of the children had antibodies to, and were presumably immune to, at least 1 dengue serotype by the age of 7 years. Most (90/103, 87%) students who became infected by dengue viruses during the study period were either asymptomatic or minimally symptomatic (absent only 1 day). Most (7/13, 53%) of the symptomatic dengue infections (absent with fever for greater than or equal to 2 days) were clinically recognized as cases of dengue hemorrhagic fever which required hospitalization. None of 47 primary dengue infections required hospitalization, whereas 7 of 56 secondary infections did (P = 0.012). Preexistent dengue immunity, as detected by conventional serologic techniques, was a significant (odds ratio greater than or equal to 6.5) risk factor for development of dengue hemorrhagic fever.     

Epidemiology of dengue and dengue hemorrhagic fever in a cohort of adults living in Bandung, West Java, Indonesia

A prospective study of dengue fever (DF) and dengue hemorrhagic fever (DHF) was conducted in a cohort of adult volunteers from two textile factories located in West Java, Indonesia. Volunteers in the cohort were bled every three months and were actively followed for the occurrence of dengue (DEN) disease. The first two years of the study showed an incidence of symptomatic DEN disease of 18 cases per 1,000 person-years and an estimated asymptomatic/ mild infection rate of 56 cases per 1,000 person-years in areas of high disease transmission. In areas where no symptomatic cases were detected, the incidence of asymptomatic or mild infection was 8 cases per 1,000 person-years. Dengue-2 virus was the predominant serotype identified, but all four serotypes were detected among the cohort. Four cases of DHF and one case of dengue shock syndrome (DSS) were identified. Three of the four DHF cases were due to DEN-3 virus. The one DSS case occurred in the setting of a prior DEN-2 virus infection, followed by a secondary infection with DEN-1 virus. To our knowledge, this is the first report of a longitudinal cohort study of naturally acquired DF and DHF in adults.     

Growth of dengue type 2 virus isolates in human peripheral blood leukocytes correlates with severe and mild dengue disease

We tested three dengue type 2 (DEN-2) isolates from children with clinically apparent but mild secondary dengue infections, and 10 isolates from children with moderately severe dengue hemorrhagic fever, and noted significant growth differences in peripheral blood leukocytes, but not in C6/36 cells. We also observed cytopathic effects in C6/36 cells that correlated with disease severity. These preliminary observations suggest the possibility that viral factors, whether surface antigens, attachment sites for entry into leukocytes, or intrinsic replication properties in human mononuclear phagocytes, might contribute to enhanced DEN infection and to the severity of the disease.     

Infections with two dengue viruses in Greece in the 20th century. Did dengue hemorrhagic fever occur in the 1928 epidemic?

From contemporary clinical accounts we hypothesized that the 1928 dengue epidemic in Greece may have been an earlier occurrence of dengue hemorrhagic fiver/dengue shock syndrome (DHF/DSS). To study the possibility that two different dengue viruses may have been involved, serums from 62 Athenians alive during the epidemic were examined for dengue antibodies; 73 per cent showed evidence of prior dengue infection. Monotypic neutralizing antibodies were found to two different dengue viruses, types 1 and 2. A large proportion of the sampled population had evidence of two or more past dengue infections. Since there is no evidence that dengue viruses have been transmitted in Greece since 1928, during the epidemic a very large number of persons immune to one dengue type must have acquired infections with a secon type. The virological criteria for secondary infection DHF/DSS are thus satisfied. Although DHF/DSS is currently restricted to Asia and the Pacific, the Greek oubreak suggests a biological potential for fatal consequences of dengue infections in Caucasians, particularly the elderly.