Clinical, epidemiologic, and virologic features of dengue in the 1998 epidemic in Nicaragua

Sustainable transfer of biotechnology to developing countries: fighting poverty by bringing scientific tools to developing-country partners

Poverty and social inequalities have powerfully sculpted not only the distribution of infectious and other diseases but also the course of disease in those affected. The lack of proper diagnosis and access to adequate health services only compounds the problem. In low-resource settings, the burden of disease can be reduced if the basic human and material resources exist to support the use of low-cost interventions by appropriately trained personnel. For 20 years, the Sustainable Sciences Institute has built scientific capacity in developing countries to recognize, prevent, and respond to the threats posed by disease.

Single-tube nested PCR using immobilized internal primers for the identification of dengue virus serotypes

Molecular techniques based on the detection of genomic sequences by reverse transcription (RT)-PCR, nested PCR, or real-time PCR have made possible the rapid diagnosis of dengue virus (DENV) infections, and these approaches have been accepted by clinical laboratories as the new standard method for the detection of dengue virus in acute-phase serum samples. One of these PCR-based assays, the two-step RT nested PCR (RT-NPCR) technique is used routinely in laboratories worldwide. In the present study, the two-step RT-NPCR as described by Lanciotti et al. [Lanciotti, R.S., Calisher, C.H., Gubler, D.J., Chang, G.J., Vorndam, A.V., 1992. Rapid detection and typing of dengue viruses from clinical samples by using reverse transcriptase-polymerase chain reaction. J. Clin. Microbiol. 30, 545-551] was adapted to a novel single-tube nested PCR (STNPCR) format, which is less prone to cross-contamination and reduces reaction cost and time. When standards for each dengue serotype were tested, the detection limit of the STNPCR was at least 10 copies for DENV-1 and 100 copies for DENV-2 and DENV-3, whereas the detection limit for the two-step RT-NPCR was 100 copies for each serotype. Sera from 22 patients with confirmed DENV-3 infections and from 14 healthy individuals were then tested in the STNPCR format using the system described by Lanciotti et al. as the reference standard. The results indicated a sensitivity of 75.9% (CI 95%, 60.3-91.4) and a specificity of 100% for the RT-STNPCR. Although RT-STNPCR was less sensitive than the conventional two-step RT-NPCR for the detection of virus in serum samples, it was still adequately sensitive, and the advantages associated with a single-tube format may outweigh the somewhat lower assay sensitivity, making it useful for diagnosis in the field.

Ultrasound measurement of gallbladder wall thickening as a diagnostic test and prognostic indicator for severe dengue in pediatric patients

Gallbladder wall thickening measured by ultrasound was significantly associated with severe dengue, as well as with hallmark features of thrombocytopenia and elevated hematocrit/hemoconcentration, in children with suspected dengue in Nicaragua. We demonstrate that gallbladder wall thickening serves as a clinically relevant diagnostic test and prognostic indicator of severe dengue in pediatric populations.

Acute disseminated encephalomyelitis in classic dengue

Neurological manifestation is uncommon in dengue infection. The pathogenesis of central nervous system involvement is controversial. We report a rare case of acute disseminated encephalomyelitis in classic dengue, with isolation of serotype 3 in liquor. This condition was associated with significant structural damage detected by magnetic resonance.

Dengue disease severity in Indonesian children: an evaluation of the World Health Organization classification system

Background

Dengue disease severity is usually classified using criteria set up by the World Health Organization (WHO). We aimed to assess the diagnostic accuracy of the WHO classification system and modifications to this system, and evaluated their potential practical usefulness.

Methods

Patients, admitted consecutively to the hospital with severe dengue, were classified using the WHO classification system and modifications to this system. Treating physicians were asked to classify patients immediately after discharge. We calculated the sensitivity of the various classification systems for the detection of shock and the agreement between the various classification systems and the treating physician's classification.

Results

Of 152 patients with confirmed dengue, sixty-six (43%) had evidence of circulatory failure. The WHO classification system had a sensitivity of 86% (95%CI 76–94) for the detection of patients with shock. All modifications to the WHO classification system had a higher sensitivity than the WHO classification system (sensitivity ranging from 88% to 99%). The WHO classification system was in only modest agreement with the intuitive classification by treating physicians whereas several modified classification systems were in good agreement.

Conclusion

The use of the WHO classification system to classify dengue disease severity is to be questioned, because it is not accurate in correctly classifying dengue disease severity and it lacks sufficient agreement with clinical practice.

Activated peripheral lymphocytes with increased expression of cell adhesion molecules and cytotoxic markers are associated with dengue fever disease

The immune mechanisms involved in dengue fever and dengue hemorrhagic/dengue shock syndrome are not well understood. The ex vivo activation status of immune cells during the dengue disease in patients was examined. CD4 and CD8 T cells were reduced during the acute phase. Interestingly, CD8 T cells co-expressing activation marker HLA-DR, Q, P, and cytolytic granule protein-Tia-1 were significantly higher in dengue patients than in controls. Detection of adhesion molecules indicated that in dengue patients the majority of T cells (CD4 and CD8) express the activation/memory phenotype, characterized as CD44HIGH and lack the expression of the naïve cell marker, CD62L LOW. Also, the levels of T cells co-expressing ICAM-1 (CD54), VLA-4, and LFA-1 (CD11a) were significantly increased. CD8 T lymphocytes expressed predominantly low levels of anti-apoptotic molecule Bcl-2 in the acute phase, possibly leading to the exhibition of a phenotype of activated/effector cells. Circulating levels of IL-18, TGF-b1 and sICAM-1 were significantly elevated in dengue patients. Early activation events occur during acute dengue infection which might contribute to viral clearance. Differences in expression of adhesion molecules among CD4 and CD8 T cells might underlie the selective extravasation of these subsets from blood circulation into lymphoid organs and/or tissues. In addition, activated CD8 T cells would be more susceptible to apoptosis as shown by the alteration in Bcl-2 expression. Cytokines such as IL-18, TGF-b1, and sICAM-1 may be contributing by either stimulating or suppressing the adaptative immune response, during dengue infection, thereby perhaps establishing a relationship with disease severity.

Dengue-3 virus genomic differences that correlate with in vitro phenotype on a human cell line but not with disease severity

We compared the full genome sequence of nine clinical isolates of dengue virus obtained during an epidemic of dengue-3 in French Polynesia in 1989, from patients with various presentations of disease. The isolates, all belonging to Genotype I, had 25 amino acid substitutions. There was no association with disease severity. When cultured in the K562 human erythroleukemia cell line, the isolates induced a range of cell growth inhibitions that was not associated with the degree of disease severity. By contrast, some substitutions--charge changes in NS1 and NS5, side-chain differences in NS1, loss of the E-153 potential glycosylation site, and 11 nucleotide insertions in the 3'UTR--that have been suggested to result in an increase or attenuation of dengue infection, appeared to be associated with the level of inhibition. These data represent the first documented study of an association between differences in the full dengue-3 genome of clinical isolates and the in vitro phenotype of these isolates on a human cell line.

Temporal distribution of dengue virus serotypes in Colombian endemic area and dengue incidence: re-introduction of dengue-3 associated to mild febrile illness and primary infection

We have investigated the temporal distribution of dengue (DEN) virus serotypes in the department (state) of Santander, Colombia, in relation to dengue incidence, infection pattern, and severity of disease. Viral isolation was attended on a total of 1452 acute serum samples collected each week from 1998 to 2004. The infection pattern was evaluated in 596 laboratory-positive dengue cases using an IgG ELISA, and PRNT test. The dengue incidence was documented by the local health authority. Predominance of DEN-1 in 1998 and DEN-3 re-introduction and predominance in 2001-2003 coincided with outbreaks. Predominance of DEN-2 in 2000-2001 coincided with more dengue hemorrhagic fever (DHF). DEN-4 was isolated in 2000-2001 and 2004 but was not predominant. There was an annual increase of primary dengue infections (from 13.7 to 81.4%) that correlated with frequency of DEN-3 (r = 0.83; P = 0.038). From the total number of primary dengue infections DEN-3 (81.3%) was the most frequent serotype. DHF was more frequent in DEN-2 infected patients than in DEN-3 infected patients: 27.5 vs 10.9% (P < 0.05). DEN-3 viruses belonged to subtype C (restriction site-specific-polymerase chain reaction) like viruses isolated in Sri-Lanka and other countries in the Americas. Our findings show the importance of continuous virological surveillance to identify the risk factors of dengue epidemics and severity.

Classifying dengue: a review of the difficulties in using the WHO case classification for dengue haemorrhagic fever

BACKGROUND

The current World Health Organisation (WHO) classification of dengue includes two distinct entities: dengue fever (DF) and dengue haemorrhagic fever (DHF)/dengue shock syndrome; it is largely based on pediatric cases in Southeast Asia. Dengue has extended to different tropical areas and older age groups. Variations from the original description of dengue manifestations are being reported.

OBJECTIVES

To analyse the experience of clinicians in using the dengue case classification and identify challenges in applying the criteria in routine clinical practice.

METHOD

Systematic literature review of post-1975 English-language publications on dengue classification.

RESULTS

Thirty-seven papers were reviewed. Several studies had strictly applied all four WHO criteria in DHF cases; however, most clinicians reported difficulties in meeting all four criteria and used a modified classification. The positive tourniquet test representing the minimum requirement of a haemorrhagic manifestation did not distinguish between DHF and DF. In cases of DHF thrombocytopenia was observed in 8.6-96%, plasma leakage in 6-95% and haemorrhagic manifestations in 22-93%. The low sensitivity of classifying DHF could be due to failure to repeat the tests or physical examinations at the appropriate time, early intravenous fluid therapy, and lack of adequate resources in an epidemic situation and perhaps a considerable overlap of clinical manifestations in the different dengue entities.

CONCLUSION

A prospective multi-centre study across dengue endemic regions, age groups and the health care system is required which describes the clinical presentation of dengue including simple laboratory parameters in order to review and if necessary modify the current dengue classification.

High seroprevalence of antibodies against dengue virus in a prospective study of schoolchildren in Managua, Nicaragua

To investigate the incidence of dengue virus (DENV) infection in Nicaragua, a 2-year prospective study was conducted in schoolchildren 4-16 years old in the capital city of Managua. Blood samples were collected before the rainy season in 2001, 2002 and 2003, and were assayed for DENV-specific antibodies. Participants were monitored for dengue-like illness, and acute and convalescent blood samples were collected from suspected dengue cases. In 2001 and 2002, 602 and 397 students were recruited, respectively, and paired annual serum samples were available from 467 and 719 participants in 2001-2002 and 2002-2003, respectively. The overall seroprevalence of anti-DENV antibodies was 91%, increasing from 75% at age 4 to 100% at age 16. The incidence of DENV infection was 12% in Year 1 and 6% in Year 2 (P < 0.001). During Year 1, four laboratory-confirmed dengue cases were detected, with one DENV2 isolate; during Year 2, there were six confirmed dengue cases, with one DENV1 isolate. These and additional circulating serotypes were confirmed by plaque reduction neutralisation test. This study demonstrates surprisingly high transmission of DENV in urban Nicaragua.

[Early indicators of dengue infection in children]

OBJECTIVE

To identify clinical manifestations and laboratory findings useful for the early diagnosis of dengue in children.

MATERIALS AND METHODS

We prospectively evaluated 125 children (aged 5 to 12 years old) with acute febrile syndrome with no apparent etiology. Paired serologic tests and/or viral culture were performed and dengue infection was confirmed in 40 patients and ruled out in 68 (17 indefinite cases). Early clinical manifestations (within the first 4 days of the disease) in the groups with dengue and other causes of febrile syndrome were compared. Independent indicators of dengue were determined in a multivariate logistic regression analysis.

RESULTS

When clinical manifestations and complete blood count were considered, the independent indicators of dengue were: absence of nasal discharge, facial flushing, and leukocyte count < or = 4,500/.l. With at least two of these findings, a sensitivity of 67 % and a specificity of 72 % for the diagnosis of dengue were obtained. When coagulation tests were considered, a model for diagnosis was composed of: absence of nasal discharge, leukocyte count < or = 4500/.l, prothrombin time > 14 seconds, and partial thromboplastin time > 29 seconds. Two of these findings suggested a diagnosis of dengue with a sensitivity of 90 % and a specificity of 52.9 %. With at least 3 findings, specificity increased to 89.7 % and sensitivity decreased to 50 %. The presence of the four components of this latter model shows a specificity of 100 %.

CONCLUSIONS

Some clinical manifestations and simple laboratory tests could aid the early detection of dengue infection in children.

Severe dengue: the need for new case definitions

Dengue fever imposes a societal burden that is difficult to measure because of the disease's non-specific symptoms and the lack of easily applied case definitions for its more severe manifestations. An efficacy trial of a tetravalent vaccine is expected in the near future, but only one of the severe dengue syndromes-the continuum of dengue haemorrhagic fever and dengue shock syndrome-is well defined. One of the results of the focus on dengue haemorrhagic fever is the false perception of low disease burden in the Americas, which is an obstacle to the mobilisation of political and economic resources to fight the disease. Three improvements are necessary to standardise the dengue haemorrhagic fever definition and to allow it to do well in different populations: (1) redefine the threshold for thrombocytopenia, (2) clarify the standard practice and value of the tourniquet test, and (3) incorporate a criterion to measure intravenous fluid replacement. In addition, for an accurate estimation of dengue burden, locally appropriate definitions of severe dengue must be devised and standardised so they will be considered valid in the global research community.

NK cells, displaying early activation, cytotoxicity and adhesion molecules, are associated with mild dengue disease

During the innate immune response against infections, Natural Killer (NK) cells are as important effector cells as are Cytotoxic T lymphocytes (CTL) generated after antigenic stimulation in the adaptative response. NK cells increase in numbers, after viral infection or vaccination. We investigated the NK cell and CD8 T lymphocyte status in 55 dengue infected patients. The NK (CD56+CD3-) and CD56+ T cell (CD56+CD3+) rates rise during the acute phase of disease. The majority of NK cells from dengue patients display early markers for activation (CD69, HLA-DR, and CD38) and cell adhesion molecules (CD44, CD11a) during the acute phase of disease. The intracellular cytotoxic granule, TIA-1, is also up-regulated early in NK cells. Most of these markers appear also on CD8+ T lymphocytes but during the late acute phase. Circulating IL-15 is elevated in a significant number of patients during early acute infection and its values were statistically correlated with NK frequencies and cytotoxic markers on NKs. We have therefore shown that dengue virus infection is very likely stimulating a cytotoxic response that may be efficient in controlling the virus in synergism with CD8+ T lymphocytes. Interestingly, the heightened CD56+CD3-, CD56+CD3+, CD56+TIA-1+ and CD56+CD11a+ cell rates are associated with mild dengue clinical manifestations and might indicate a good prognosis of the disease.

The 2001 dengue epidemic in Chennai

Dengue is emerging as a serious public health problem in Tamil Nadu. The present surveillance system is unlikely to generate proper information on the epidemiology of the disease, which is essential for planning and development of relevant control/preventive measures against dengue.

OBJECTIVE

Between November 2001 and January 2002, a descriptive study was undertaken on children with clinical dengue attending Kanchi Kamakoti Child Trust Hospital (KKCTH, a major private referral pediatric hospital in Tamil Nadu, India) to define the magnitude of dengue burden, the natural history of this disease in terms of clinical presentation, and outcome of the infections in hospitalized children (< 15) with clinical dengue.

METHODS

The sera collected from patients analyzed for dengue specific IgM and IgG antibodies by IgM, IgG antibody capture enzyme linked immunosorbent assay (ELISA) using alternatively two commercial kits. World Health Organization clinical case definition was adopted to categorize the dengue confirmed children.

RESULTS

Dengue was diagnosed in 74.5% (143) of the 192 hospitalized children with clinical dengue. A considerable proportion (20%) of the total dengue infections were constituted by infants less than 1 yr of age. DF [dengue fever], DHF [dengue hemorrhagic fever] and DSS [dengue shock syndrome] were diagnosed in 65%, 11.2% and 23.8% of 143 dengue confirmed patients respectively. Though severe dengue (DSS + DHF) was present in 35% of the patients, the mortality rate was low during the study period due to timely diagnosis and clinical management of the patients.

CONCLUSION

In developing countries like India, building of laboratory capacity for diagnosis and combat-mode ready preparedness for the management of dengue cases in emergency situation may reduce dengue-related mortality. This can be achieved in a wider scale through an integrated approach through the community, professionals and the public health departments.

Immunoglobulin M enzyme-linked immunosorbent assay using recombinant polypeptides for diagnosis of dengue

We demonstrate that a mixture of four recombinant dengue virus E polypeptides corresponding to the N-terminal region of the envelope protein from all serotypes substitutes for standard antigens in two immunoglobulin M enzyme-linked immunosorbent assay formats with 100% concordance, making these polypeptides a useful and accessible reagent for serological diagnosis of dengue in endemic countries.

Dengue and dengue hemorrhagic fever, Brazil, 1981-2002

Brazil has experienced an increase in dengue disease severity in the past 5 years.

In the last 5 years, Brazil has accounted for ≈70% of reported dengue fever cases in the Americas. We analyzed trends of dengue and dengue hemorrhagic fever (DHF) from the early 1980s to 2002 by using surveillance data from the Brazilian Ministry of Health. Two distinct epidemiologic patterns for dengue were observed: localized epidemics (1986–1993), and endemic and epidemic virus circulation countrywide (1994–2002). Currently, serotypes 1, 2, and 3 cocirculate in 22 of 27 states. Dengue and DHF affected mainly adults; however, an increase in occurrence of DHF among children has been recently detected in northern Brazil, which suggests a shift in the occurrence of severe disease to younger age groups. In 2002, hospitalizations increased, which points out the change in disease severity compared to that seen in the 1990s. We describe the epidemiology of dengue in Brazil, characterizing the changing patterns of it and DHF during the last 20 years.

Dengue fever: new paradigms for a changing epidemiology

Dengue is the most important arthropod-borne viral disease of public health significance. Compared with nine reporting countries in the 1950s, today the geographic distribution includes more than 100 countries worldwide. Many of these had not reported dengue for 20 or more years and several have no known history of the disease. The World Health Organization estimates that more than 2.5 billion people are at risk of dengue infection. First recognised in the 1950s, it has become a leading cause of child mortality in several Asian and South American countries.

This paper reviews the changing epidemiology of the disease, focusing on host and societal factors and drawing on national and regional journals as well as international publications. It does not include vaccine and vector issues. We have selected areas where the literature raises challenges to prevailing views and those that are key for improved service delivery in poor countries.

Shifts in modal age, rural spread, and social and biological determinants of race- and sex-related susceptibility have major implications for health services. Behavioural risk factors, individual determinants of outcome and leading indicators of severe illness are poorly understood, compromising effectiveness of control programmes. Early detection and case management practices were noted as a critical factor for survival. Inadequacy of sound statistical methods compromised conclusions on case fatality or disease-specific mortality rates, especially since the data were often based on hospitalised patients who actively sought care in tertiary centres.

Well-targeted operational research, such as population-based epidemiological studies with clear operational objectives, is urgently needed to make progress in control and prevention.

Short Communication: Detection of dengue virus antigens in desiccated mosquitoes: an improved tool for surveillance

We developed a surveillance tool to monitor dengue virus (DENV) infection in vector mosquitoes using a dengue antigen-capture enzyme immunoassay (EIA) on desiccated specimens stored at room temperature (RT). We tested the effect of storage on the stability of DEN1, DEN2, DEN3 and DEN4 antigens. Although desiccated infected Aedes aegypti mosquitoes stored between 31 and 34 degrees C (RT) showed greater reactivity in the EIA than those stored at -80 degrees C, a significant difference between the two was observed only with DEN2. Storage between 31 and 34 degrees C for up to 4 weeks (the longest period tested) did not affect the reactivity in the EIA, indicating the stability of DENV antigens.

A epidemia de dengue/dengue hemorrágico no município do Rio de Janeiro, 2001/2002

O objetivo deste estudo foi avaliar a ocorrência dos principais sinais e sintomas dos casos de dengue clássico e dengue hemorrágico na epidemia de 2001-2002 do município do Rio de Janeiro. Foram analisados os 155.242 casos notificados ao Sistema de Informações de Agravos de Notificação, desde janeiro/2001, até junho/2002; deste total, excluindo-se os ignorados, 81.327 casos foram classificados como dengue clássico e 958 como dengue hemorrágico, com um total de 54 óbitos. Avaliaram-se as variáveis referentes à sintomatologia da doença. Manifestações gerais como febre, cefaléia, prostração, mialgia, náuseas e dor retro-orbitária tiveram alta incidência tanto no dengue clássico como no dengue hemorrágico. Por outro lado, manifestações hemorrágicas e algumas de maior gravidade como choque, hemorragia digestiva, petéquias, epistaxe, dor abdominal e derrame pleural, estiveram significativamente associadas ao dengue hemorrágico. Além disso, a evolução do quadro clínico para o óbito foi 34,8 vezes maior no dengue hemorrágico que no dengue clássico (OR=34,8; IC 19,7-61,3).

Microevolution and virulence of dengue viruses

The evolution of dengue viruses has had a major impact on their virulence for humans and on the epidemiology of dengue disease around the world. Although antigenic and genetic differences in virus strains had become evident, it is mainly due to the lack of animal models of disease that has made it difficult to detect differences in virulence of dengue viruses. However, phylogenetic studies of many different dengue virus samples have led to the association between specific genotypes (within serotypes) and the presentation of more or less severe disease. Currently, dengue viruses can be classified as being of epidemiologically low, medium, or high impact; i.e., some viruses may remain in sylvatic cycles of little or low transmissibility to humans, others produce dengue fever (DF) only, and some genotypes have been associated with the potential to cause the more severe dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) in addition to DF. Although the factors that contribute to dengue virus epidemiology are complex, studies have suggested that specific viral structures may contribute to increased replication in human target cells and to increased transmission by the mosquito vector; however, the immune status and possibly the genetic background of the host are also determinants of virulence or disease presentation. As to the question of whether dengue viruses are evolving toward virulence as they continue to spread throughout the world, phylogenetic and epidemiological analyses suggest that the more virulent genotypes are now displacing those that have lower epidemiological impact; there is no evidence for the transmission of antigenically aberrant, new strains.

Fluid intake and decreased risk for hospitalization for dengue fever, Nicaragua

In a hospital and health center-based study in Nicaragua, fluid intake during the 24 hours before being seen by a clinician was statistically associated with decreased risk for hospitalization of dengue fever patients. Similar results were obtained for children <15 years of age and older adolescents and adults in independent analyses.

Elevated levels of total and dengue virus-specific immunoglobulin E in patients with varying disease severity

The kinetics of total and dengue virus-specific immunoglobulin E (IgE) were studied in serial serum samples obtained from 168 patients, 41 of whom suffered from primary dengue virus infection and 127 suffered from secondary dengue virus infection. Seventy-one patients were classified as dengue fever, 30 as dengue hemorrhagic fever, and 67 as dengue shock syndrome. A control group included single serum samples from patients with a herpes virus infection (n = 14), non-dengue febrile patients (n = 10), and healthy blood donors (n = 10). Patients with dengue virus infection had higher levels of total and dengue virus-specific IgE than non-dengue patients (P < 0.05). Patients with secondary dengue virus infections had not significantly increased levels of both total and dengue virus-specific IgE in the acute phase of disease compared to patients with primary dengue virus infections. Dengue virus-specific IgE was significantly higher in dengue hemorrhagic fever and/or dengue shock syndrome patients compared to dengue fever and non-dengue patients (P < 0.05). In conclusion, this study showed elevated total and dengue virus-specific IgE serum antibody levels in the acute stage of disease. Therefore, measurement of both total and dengue virus-specific IgE serum antibodies can be used as an additional prognostic marker in the development of severe complications in dengue virus infections. In addition, the presence and increase of dengue virus-specific IgE serum antibodies in patients with dengue virus infections is suggestive of the pathogenetic role that IgE may play in the hemostatic disorders observed in dengue hemorrhagic fever and dengue shock syndrome.

American genotype structures decrease dengue virus output from human monocytes and dendritic cells

The dengue virus type 2 structures probably involved in human virulence were previously defined by sequencing the complete genome of both American and Southeast (SE) Asian genotype templates in patient serum (K. C. Leitmeyer et al., J. Virol. 73:4738-4747, 1999). We have now evaluated the effects of introducing a mutation in the envelope glycoprotein (E) gene and/or replacement of 5'- and 3'-nontranslated regions on dengue virus replication in human primary cell cultures. A series of chimeric infectious clones were generated containing different combinations of American and SE Asian genotype sequences. Some of the chimeric viruses had altered plaque morphology in mammalian cells; however, they replicated at similar rates in mosquito cells as measured by quantitative reverse transcription-PCR and plaque assay. Although susceptibility to virus infection varied from donor to donor in experiments using human macrophage and dendritic cells, we were able to measure consistent differences in viral RNA output per infected cell. Using this measurement, we demonstrated that the chimeric virus containing the E mutation had a lower virus output compared to the parental infectious clone. A larger reduction in virus output was observed for the triple mutant and the wild-type, American genotype virus from which chimeric inserts were derived. It appears that the three changes function synergistically, although the E mutation alone gives a lower output compared to the 5'- and 3'-terminal mutations. The data suggest that these changes may be responsible for decreased dengue virus replication in human target cells and for virulence characteristics during infection.

Diagnosis of dengue virus infection by detection of specific immunoglobulin M (IgM) and IgA antibodies in serum and saliva

To evaluate alternative approaches to the serological diagnosis of dengue virus (DEN) infection, the detection of DEN-specific immunoglobulin M (IgM) and IgA antibodies in serum and saliva specimens was assessed in 147 patients with symptoms of DEN infection seen at the Ministry of Health in Nicaragua. Seventy-two serum samples were determined to be positive for anti-DEN antibodies by IgM capture enzyme-linked immunosorbent assay, the routine diagnostic procedure. Serum and saliva specimens were obtained from 50 healthy adults as additional controls. IgM was detected in the saliva of 65 of the 72 serum IgM-positive cases, 6 of the 75 serum IgM-negative cases, and none of the control group, resulting in a sensitivity of 90.3% and a specificity of 92.0% and demonstrating that salivary IgM is a useful diagnostic marker for DEN infection. Detection of IgA in serum may be another feasible alternative for the diagnosis of DEN infection, with serum IgA found in 68 (94.4%) of the IgM-positive cases. In contrast, detection of IgA in saliva was not found to be a useful tool for DEN diagnosis in the present study. Further studies of the kinetics of antibody detection in another set of 151 paired acute- and convalescent-phase serum samples showed that DEN-specific IgA antibodies were detected in more acute-phase samples than were IgM antibodies. Thus, we conclude that DEN-specific IgA in serum is a potential diagnostic target. Furthermore, given that saliva is a readily obtainable, noninvasive specimen, detection of DEN-specific salivary IgM should be considered a useful, cheaper diagnostic modality with similar sensitivity and specificity to IgM detection in serum.

Viral agents as biological weapons and agents of bioterrorism

Multiple viral agents have been classified by the CDC as potential weapons of mass destruction or agents for biologic terrorism. Agents such as smallpox, viral hemorrhagic fever viruses, agents of viral encephalitis, and others are of concern because they are highly infectious and relatively easy to produce. Although dispersion might be difficult, the risk is magnified by the fact that large populations are susceptible to these agents and only limited treatment and vaccination strategies exist. Although the risk of large-scale bioterrorism using viral agents is small, public health programs and health care providers must be prepared for this potentially devastating impact on public health.