Comparison of rapid centrifugation assay with conventional tissue culture method for isolation of dengue 2 virus in C6/36-HT cells

Electropolymerized-molecularly imprinted polymers (E-MIPS) as sensing elements for the detection of dengue infection

A straightforward in situ detection method for dengue infection was demonstrated through the molecular imprinting of a dengue nonstructural protein 1 (NS1) epitope into an electropolymerized molecularly imprinted polyterthiophene (E-MIP) film sensor. The key enabling step in the sensor fabrication is based on an epitope imprinting strategy, in which short peptide sequences derived from the original target molecules were employed as the main template for detection and analysis. The formation of the E-MIP sensor films was facilitated using cyclic voltammetry (CV) and monitored in situ by electrochemical quartz crystal microbalance (EC-QCM). Surface properties were analyzed using different techniques including atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and polarization modulation-infrared reflection-adsorption (PM-IRRAS). The standard calibration curve (R = 0.9830) was generated for the detection of the epitope, Ac-VHTWTEQYKFQ-NH₂, with a linear range of 0.2 to 30 μg/mL and detection limit of 0.073 μg/mL. A separate calibration curve (R = 0.9786) was obtained using spiked buffered solutions of dengue NS1 protein, which resulted in a linear range of 0.2 to 10 μg/mL and a detection limit of 0.056 μg/mL. The fabricated E-MIP sensor exhibited long-term stability, high sensitivity, and good selectivity towards the targeted molecules. These results indicated that the formation of the exact and stable cavity imprints in terms of size, shape, and functionalities was successful. In our future work, we aim to use our E-MIP sensors for NS1 detection in real-life samples such as serum and blood.

Differential replicative fitness of the four dengue virus serotypes circulating in Colombia in human liver Huh7 cells

Dengue has been a significant public health problem in Colombia since the simultaneous circulation of the four dengue virus serotypes. The replicative fitness of dengue is a biological feature important for virus evolution and contributes to elucidating the behavior of virus populations and viral pathogenesis. However, it has not yet been studied in Colombian isolates. This study aimed to compare the replicative fitness of the four dengue virus serotypes and understand the association between the serotypes, their in vitro infection ability, and their replication in target cells. We used three isolates of each DENV serotype to infect Huh-7 cells at an MOI of 0.5. The percentage of infected cells was evaluated by flow cytometry, cell viability was evaluated by MTT assay, and the pathogenicity index was calculated as a ratio of both parameters. The replicative fitness was measured by the number of viral genome copies produced using quantitative PCR and the production of infectious viral progeny was measured by plaque assay. We showed that Huh-7 cells were susceptible to infection with all the different strain isolates. Nevertheless, the biological characteristics, such as infectious ability and cell viability, were strain-dependent. We also found different degrees of pathogenicity between strains of the four serotypes, representative of the heterogeneity displayed in the circulating population. When we analyzed the replicative fitness using the mean values obtained from RT-qPCR and plaque assay for the different strains, we found serotype-dependent behavior. The highest mean values of replicative fitness were obtained for DENV-1 (log 4.9 PFU/ml) and DENV-4 (log 5.28 PFU/ml), followed by DENV-2 (log 3.9 PFU/ml) and DENV-3 (log 4.31 PFU/ml). The internal heterogeneity of the replicative fitness within each serotype could explain the simultaneous circulation of the four DENV serotypes in Colombia.

OSBPL10, RXRA and lipid metabolism confer African-ancestry protection against dengue haemorrhagic fever in admixed Cubans

Ethnic groups can display differential genetic susceptibility to infectious diseases. The arthropod-born viral dengue disease is one such disease, with empirical and limited genetic evidence showing that African ancestry may be protective against the haemorrhagic phenotype. Global ancestry analysis based on high-throughput genotyping in admixed populations can be used to test this hypothesis, while admixture mapping can map candidate protective genes. A Cuban dengue fever cohort was genotyped using a 2.5 million SNP chip. Global ancestry was ascertained through ADMIXTURE and used in a fine-matched corrected association study, while local ancestry was inferred by the RFMix algorithm. The expression of candidate genes was evaluated by RT-PCR in a Cuban dengue patient cohort and gene set enrichment analysis was performed in a Thai dengue transcriptome. OSBPL10 and RXRA candidate genes were identified, with most significant SNPs placed in inferred weak enhancers, promoters and lncRNAs. OSBPL10 had significantly lower expression in Africans than Europeans, while for RXRA several SNPs may differentially regulate its transcription between Africans and Europeans. Their expression was confirmed to change through dengue disease progression in Cuban patients and to vary with disease severity in a Thai transcriptome dataset. These genes interact in the LXR/RXR activation pathway that integrates lipid metabolism and immune functions, being a key player in dengue virus entrance into cells, its replication therein and in cytokine production. Knockdown of OSBPL10 expression in THP-1 cells by two shRNAs followed by DENV2 infection tests led to a significant reduction in DENV replication, being a direct functional proof that the lower OSBPL10 expression profile in Africans protects this ancestry against dengue disease.

Dengue is a concern of worldwide health authorities given the increase on virus and vector dispersions. So far only one traditional GWAS survey has been performed in Vietnamese children. This disease is also epidemic in tropical and subtropical regions of the Americas, where most populations descend from a dynamic admixture between African, European and Native American backgrounds. Empirical evidence claimed that African descent was protective against dengue haemorrhagic phenotype in the Cuban population, and this study is the first to apply admixture mapping to identify candidate genes that confer African protection. We also present evidence that two candidate genes, OSBPL10 and RXRA, are differentially expressed along dengue disease progression in Cuban patients and in a Thai dengue transcriptome dataset, and directly show that knockdown of OSBPL10 gene expression leads to a significant reduction in DENV2 replication. A very important overall result of our work is that it provides a unifying framework for many genes that have been said to be protective in dengue. Our evidence places the LXR/RXR activation pathway at the center of natural dengue protection, and supports pursuing therapeutic techniques involving synthetic ligands of nuclear receptor genes or kinases inhibitors that interact with proteins involved in lipid metabolism.

Role of CC chemokine receptor 1 and two of its ligands in human dengue infection. Three approaches under the Cuban situation

Any of the four dengue serotypes can cause a severe disease, partly due to systemic inflammation orchestrated by mediators like cytokines and chemokines. We addressed the role of CCR1 and its ligands CCL3/MIP-1α and CCL5/RANTES in dengue infection using three different approaches: an ex vivo model exploring memory immune response in subjects with a well characterized dengue immune background, an in vivo study in patients with primary or secondary dengue infection, and an approach in fatal dengue. CCR1 and CCL3/MIP-1α gene expression showed differences after homotypic and heterotypic challenge according to dengue immune background of subjects, in correspondence with previous observations in Cuban dengue outbreaks. CCL5/RANTES gene expression was higher after homotypic challenge. CCR1 and CCL3/MIP-1α gene expression was higher in patients with secondary infection during critical days of the dengue disease, while the increase in RANTES expression started earlier than the observed for CCR1 and CCL3/MIP-1α. CCR1 and CCL3/MIP-1α gene expression was as high in brain as in spleen tissue from necropsy. Our results confirm the strong influence of previous immunity in subsequent dengue infections, and confer a possible pathogenic role to CCR1 and CCL3/MIP-1α in dengue disease and a possible protective role for CCL5/RANTES, probably through CCR5 interaction.

Comparison of surface plasmon resonance, resonant waveguide grating biosensing and enzyme linked immunosorbent assay (ELISA) in the evaluation of a dengue virus immunoassay

Two label-free biosensor platforms, Resonance Waveguide Grating (RWG) and Surface Plasmon Resonance (SPR), were used to rank a large panel of anti-dengue virus NS1 antibodies. Dengue non-structural 1 (NS1) protein is an established serological marker for the early detection of dengue infection. A variety of commercial dengue NS1 antigen capture immunoassays are available in both ELISA and lateral flow format. However, there is a significant scope to improve both the sensitivity and the specificity of those tests. The interactions of antibody (Ab)-antigen (Ag) were profiled, with weak interactions (K_D= 1–0.1 μM) able to be detected under static equilibrium conditions by RWG, but not observed to under more rigorous flow conditions using SPR. There were significant differences in the absolute affinities determined by the two technologies, and there was a poor correlation between antibodies best ranked by RWG and the lower limit of detection (LLOD) found by ELISA. Hence, whilst high-throughput RWG can be useful as preliminary screening for higher affinity antibodies, care should be exercised in the assignation of quantitative values for affinity between different assay formats.

Understanding the dengue viruses and progress towards their control

Traditionally, the four dengue virus serotypes have been associated with fever, rash, and the more severe forms, haemorrhagic fever and shock syndrome. As our knowledge as well as understanding of these viruses increases, we now recognise not only that they are causing increasing numbers of human infections but also that they may cause neurological and other clinical complications, with sequelae or fatal consequences. In this review we attempt to highlight some of these features in the context of dengue virus pathogenesis. We also examine some of the efforts currently underway to control this "scourge" of the tropical and subtropical world.

Dengue virus identification by transmission electron microscopy and molecular methods in fatal dengue hemorrhagic fever

Dengue virus is the most significant virus transmitted by arthropods worldwide and may cause a potentially fatal systemic disease named dengue hemorrhagic fever. In this work, dengue virus serotype 4 was detected in the tissues of one fatal dengue hemorrhagic fever case using electron immunomicroscopy and molecular methods. This is the first report of dengue virus polypeptides findings by electron immunomicroscopy in human samples. In addition, not-previously-documented virus-like particles visualized in spleen, hepatic, brain, and pulmonary tissues from a dengue case are discussed.

Population structure of the dengue viruses, Aragua, Venezuela, 2006-2007. Insights into dengue evolution under hyperendemic transmission

During the past three decades there has been a notable increase in dengue disease severity in Venezuela. Nevertheless, the population structure of the viruses being transmitted in this country is not well understood. Here, we present a molecular epidemiological study on dengue viruses (DENV) circulating in Aragua State, Venezuela during 2006-2007. Twenty-one DENV full-length genomes representing all of the four serotypes were amplified and sequenced directly from the serum samples. Notably, only DENV-2 was associated with severe disease. Phylogenetic trees constructed using Bayesian methods indicated that only one genotype was circulating for each serotype. However, extensive viral genetic diversity was found in DENV isolated from the same area during the same period, indicating significant in situ evolution since the introduction of these genotypes. Collectively, the results suggest that the non-structural (NS) proteins may play an important role in DENV evolution, particularly NS1, NS2A and NS4B proteins. The phylogenetic data provide evidence to suggest that multiple introductions of DENV have occurred from the Latin American region into Venezuela and vice versa. The implications of the significant viral genetic diversity generated during hyperendemic transmission, particularly in NS protein are discussed and considered in the context of future development and use of human monoclonal antibodies as antivirals and tetravalent vaccines.

Molecular epidemiology of yellow fever in Bolivia from 1999 to 2008

Yellow fever (YF) is a serious public health problem in Bolivia since at least the 19th century. Surprisingly, very limited information has been made available to date regarding the genetic characterisation and epidemiology of Bolivian YF virus (YFV) strains. Here, we conducted the genetic characterization of 12 human isolates of YFV collected in Bolivia between 1999 and 2008, by sequencing and analysis of two regions of the viral genome: a fragment encoding structural proteins "PrM" (premembrane and envelope) and a distal region "EMF," spanning the end of the virus genome. Our study reveals a high genetic diversity of YFV strains circulating in Bolivia during the last decade: we identified not only "Peruvian-like" genotype II viruses (related to previously characterized Bolivian strains), but also, for the fist time, "Brazilian-like" genotype I viruses. During the complete period of the study, only cases of "jungle" YF were detected (i.e., circulation of YFV via a sylvatic cycle) with no cluster of urban cases. However, the very significant spread of the Aedes aegypti mosquito across Bolivian cities threatens the country with the reappearance of an urban YFV transmission cycle and thus is required a sustained epidemiological surveillance.

Secondary heterologous dengue infection risk: Disequilibrium between immune regulation and inflammation?

Increased serum levels of cytokines released by cells of the immune response have been detected in patients suffering from dengue disease. Likewise, secondary infections by a different dengue virus serotype result in a highest risk of development of the severe dengue disease. Both findings suggest that the memory immune response is one of the key players in the pathogenesis of this disease. Here we take advantage of the particular Cuban epidemiological situation in dengue to analyze a broad spectrum of cell-mediated immune response mediators at mRNA and protein level. Evidences for a regulatory immune pattern in homologous (TGF-beta, IL-10) vs. pro-inflammatory pattern (IFN-gamma, TNF-alpha) in heterologous dengue virus re-challenge were found, suggesting a possible association with the higher incidence of severe dengue cases in the latter case.

Isolation and identification of a canine coronavirus strain from giant pandas (Ailuropoda melanoleuca)

Two giant pandas (Ailuropoda melanoleuca) died of unknown causes in a Chinese zoo. The clinical disease profile suggested that the pandas may have suffered a viral infection. Therefore, a series of detection including virus isolation, electron microscopy, cytobiological assay, serum neutralization and RT-PCR were used to identify the virus. It was determined that the isolated virus was a canine coronavirus (CCV), on the basis of coronavirus, neutralization by canine anti-CCV serum, and 84.3% to 100% amino acid sequence similarity with CCV. The results suggest that the affected pandas had been infected with CCV.

Molecular epidemiological analysis of dengue fever in Bolivia from 1998 to 2008

Dengue fever was first recognized in Bolivia in 1931. However, very limited information was available to date regarding the genetic characterization and epidemiology of Bolivian dengue virus strains. Here, we performed genetic characterization of the full-length envelope gene of 64 Bolivian isolates from 1998 to 2008 and investigated their origin and evolution to determine whether strains circulated simultaneously or alternatively, and whether or not multiple introductions of distinct viral variants had occurred during the period studied. We determined that, during the last decade, closely related viruses circulated during several consecutive years (5, 6, and 6 years for DENV-1, DENV-2, and DENV-3, respectively) and the co-circulation of two or even three serotypes was observed. Emergence of new variants (distinct from those identified during the previous episodes) was identified in the case of DENV-1 (2007 outbreak) and DENV-2 (2001 outbreak). In all cases, it is likely that the viruses originated from neighboring countries.

Dengue: where are we today?

Dengue is considered the main arthropod-borne viral disease of humans. In the last few years, an increasing number of reports of mild and severe cases have been reported. The growing dengue incidence observed in recent years has been accompanied by reports of new observations, findings and global initiatives with an improvement in our understanding of this phenomenon. The epidemiology and new clinical classification of dengue, advances in the diagnostic and pathogenesis knowledge, and vaccine development as well as control methods including new global initiatives are summarised here.

Phage-displayed antibody fragments recognizing dengue 3 and dengue 4 viruses as tools for viral serotyping in sera from infected individuals

The current study shows the usefulness of dengue-3- and dengue-4-specific phage-displayed antibody fragments as tools for viral detection and serotyping in sera from infected individuals. C6/36 HT cells were inoculated with acute-phase sera from patients, and supernatants were collected daily and analyzed by ELISA using phage-displayed antibody fragments as serotype-specific detector reagents. Serotyping of most samples was possible as early as two to three days postinoculation. Results were comparable with those obtained by indirect immunofluorescence assay but were obtained in a shorter period of time (<1 week). Phage-displayed antibody fragments were better tools for diagnosis and serotyping than their soluble counterparts. Our approach combines the advantages of viral isolation and ELISA techniques. These results could be the basis for the development of a high-throughput method for identifying dengue virus serotypes, which is crucial for the management and control of the disease.

Monoclonal antibody to dengue capsid protein: its application in dengue studies

Dengue fever (DF) and dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) are considered the most important arthropod-borne viral diseases in terms of morbidity and mortality. The emergency and severity of dengue (Den) infections increase the necessity of an early, quick and effective dengue laboratory diagnostic. Viral isolation is considered a gold standard for diagnosis of dengue infection using monoclonal antibodies (mAbs) as a tool for determining serotype specificity. Alternatives have been used to improve sensitivity and time to dengue diagnosis. Based on the early expression of dengue C protein in the life cycle, we focused our study on the application of an anti-dengue 2 virus capsid protein mAb in dengue diagnosis. The kinetic expression of dengue-2 capsid in mosquito cells and its immuno-localization in experimentally infected suckling albin Swiss (OF-1) mice brain tissues was established. The results demonstrate the possible utility of this mAb in early dengue diagnosis versus traditional isolation. In addition, a preliminary study of an enzyme immunoassay method using 8H8 mAb for specific detection of dengue C protein antigen was performed, making possible recombinant C protein quantification. The results suggest that detection of dengue capsid protein could be useful in the diagnosis of early dengue infection.

Primary and secondary infections of Macaca fascicularis monkeys with Asian and American genotypes of dengue virus 2

The goal of this study was to compare the immune response and the protection capacity induced by the dengue virus 2 (DENV-2) American and Asian genotypes in Macaca fascicularis monkeys. Animals were infected with American or Asian DENV-2 strains and challenged 1 year later with a DENV-2 Asian genotype strain. The viremia and monkey antibody levels were similar for the different strains after primary and secondary infection; however, the functionality of the antibody response was different. A limited viral replication was demonstrated after the secondary infection in all the monkeys. No virus was isolated in tissue culture, while reverse transcription-PCR showed a late positive reaction in four of five challenged monkeys. The immunoglobulin M response pattern and the detection of antibodies to specific proteins by Western blotting supported the protection data. Despite the demonstration of the protective effect after homologous challenge, a strong anamnestic antibody response was observed.

Application of modified shell vial culture procedure for arbovirus detection

The isolation of arboviruses from patient's low titer sera can be difficult. Here we compared the detection efficiency of Dengue (DEN), Yellow Fever (YF), Saint Louis Encephalitis (SLE), West Nile (WN), Ilheus (ILH), Group C (GC), Oropouche (ORO), Mayaro (MAY) and Venezuela Encephalitis Equine (VEE) viruses using a Modified Shell Vial Culture (MSVC) protocol to a Standard Cell Culture (SCC) protocol. First the MSVC and SCC protocols were compared using five dilutions for each of the following stock viruses: DEN-1, DEN-2, DEN-3, DEN-4, YF, SLE, WN, ILH, GC, ORO, MAY and VEE. Next, patients' original sera from which viruses (DEN-1, DEN-2, DEN-3, YF, GC, ORO, MAY and VEE) had been previously isolated were compare by the two methods using five sera dilutions. In addition, seven sera that were positive for DEN-3 by RT-PCR and negative by SCC were processed by MSVC. The MSVC protocol was consistently 1-2 logs higher virus dilution more sensitive for virus detection than the SCC protocol for all stock Flaviviruses tested (DEN-1, DEN-2, DEN-3, DEN-4, YF, SLE, WN and ILH). MSVC was equal to or one log more sensitive for virus detection than SCC for the stock Bunyaviruses (GC and ORO). For the stock Alphavirus MAY, MSVC was equally or one log more sensitive for virus detection than SCC, while for VEE SCC was equally or one log more sensitive for virus detection than MSVC. MSVC was consistently one to two sera dilutions more sensitive than SCC for the detection of Flaviviruses from patients' sera. Both methods were approximately equally sensitive for the detection of Bunyaviruses from patients' sera and equal or one dilution less sensitive for the detection of Alphaviruses from patients' sera. Additionally, MSVC detected DEN virus in five of seven DEN-3 RT-PCR positive, SCC negative patients' sera.

Characterization of the early events in dengue virus cell entry by biochemical assays and single-virus tracking

In this study, we investigated the cell entry characteristics of dengue virus (DENV) type 2 strain S1 on mosquito, BHK-15, and BS-C-1 cells. The concentration of virus particles measured by biochemical assays was found to be substantially higher than the number of infectious particles determined by infectivity assays, leading to an infectious unit-to-particle ratio of approximately 1:2,600 to 1:72,000, depending on the specific assays used. In order to explain this high ratio, we investigated the receptor binding and membrane fusion characteristics of single DENV particles in living cells using real-time fluorescence microscopy. For this purpose, DENV was labeled with the lipophilic fluorescent probe DiD (1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine, 4-chlorobenzenesulfonate salt). The surface density of the DiD dye in the viral membrane was sufficiently high to largely quench the fluorescence intensity but still allowed clear detection of single virus particles. Fusion of the viral membrane with the cell membrane was evident as fluorescence dequenching. It was observed that DENV binds very inefficiently to the cells used, explaining at least in part the high infectious unit-to-particle ratio. The particles that did bind to the cells showed different types of transport behavior leading to membrane fusion in both the periphery and perinuclear regions of the cell. Membrane fusion was observed in 1 out of 6 bound virus particles, indicating that a substantial fraction of the virus has the capacity to fuse. DiD dequenching was completely inhibited by ammonium chloride, demonstrating that fusion occurs exclusively from within acidic endosomes.

Role of cell culture for virus detection in the age of technology

Viral disease diagnosis has traditionally relied on the isolation of viral pathogens in cell cultures. Although this approach is often slow and requires considerable technical expertise, it has been regarded for decades as the "gold standard" for the laboratory diagnosis of viral disease. With the development of nonculture methods for the rapid detection of viral antigens and/or nucleic acids, the usefulness of viral culture has been questioned. This review describes advances in cell culture-based viral diagnostic products and techniques, including the use of newer cell culture formats, cryopreserved cell cultures, centrifugation-enhanced inoculation, precytopathogenic effect detection, cocultivated cell cultures, and transgenic cell lines. All of these contribute to more efficient and less technically demanding viral detection in cell culture. Although most laboratories combine various culture and nonculture approaches to optimize viral disease diagnosis, virus isolation in cell culture remains a useful approach, especially when a viable isolate is needed, if viable and nonviable virus must be differentiated, when infection is not characteristic of any single virus (i.e., when testing for only one virus is not sufficient), and when available culture-based methods can provide a result in a more timely fashion than molecular methods.

PCR detection of dengue virus using dried whole blood spotted on filter paper

Whole blood dried onto filter paper constitutes a potentially useful material for molecular testing of viruses, including dengue. In order to assess the stability of viral RNA, we carried out dengue-RNA detection in whole blood infected with dengue virus that had been previously spotted onto filter paper. Filter papers were stored at room temperature, 4 and -70 degrees C and processed for PCR assay at intervals of 2, 4, 6 and 9 weeks. Our results demonstrated that dengue-RNA was stable in filter paper for 9 weeks at all tested temperatures. Furthermore, we evaluated these conditions using frozen sera and dried blood samples onto filter paper from 52 patients with confirmed clinical diagnosis of dengue infection. PCR results showed a 100% specificity and 93% sensitivity for dried blood samples. This storage method facilitates the transportation and analysis by nucleic acid amplification techniques even when freezing conditions are not available.

Virus evolution during a severe dengue epidemic in Cuba, 1997

Full-length genomic sequences from six DENV-2 isolates sampled at different times during a dengue outbreak that occurred in Cuba in 1997 were determined. Phylogenetic analysis indicated that these isolates fall into the "American/Asian" genotype. Genome analysis revealed strong conservation of the structural proteins and the non-coding regions (5' NCR and 3' NCR). Nucleotide substitutions were observed in non-structural genes and most notably in the NS5 gene. There was a clear pattern of virus evolution during the epidemic; the earliest isolates sampled differed from those sampled later by amino acid replacements in the NS1 and NS5 proteins, although there was no evidence that these represented escape mutants. Further studies are therefore required to define the functional role of amino acid replacements observed and their possible relation to disease severity.

IL-10 levels in Dengue patients: Some findings from the exceptional epidemiological conditions in Cuba

The pathogenesis associated with Dengue haemorrhagic fever, has yet to be fully elucidated, with no definitive in vivo evidence. The exceptional epidemiological circumstances in Cuba allow the evaluation of different mediators in a well-defined situation. In the present study, we describe the determination of levels of IL-12, IL-10 and RANTES in the sera of Cuban patients hospitalised with Dengue fever or Dengue haemorrhagic fever. The results showed that levels of serum IL-10 were higher in patients than controls, and those patients with secondary infections had consistently higher levels. All the Dengue haemorrhagic fever patients had increased levels of IL-10. In contrast, levels of IL-12 did not differ between patients and controls. Finally, RANTES serum levels detected in patients were lower than those observed in the controls. The association of increased levels of IL-10 in Dengue patients with a sequential infection suggests a possible role of this cytokine in the pathogenesis of Dengue disease.

Dengue diagnosis, advances and challenges

Dengue diagnosis was one of the topics discussed at the symposium 'The Global Threat of Dengue - Desperately Seeking Solutions' organized during the 10th International Congress of Infectious Diseases held in Singapore in 2002. In this paper, a review is presented focusing on the main advances, problems and challenges of dengue diagnosis.IgM capture ELISA, virus isolation in mosquito cell lines and live mosquitoes, dengue specific monoclonal antibodies and PCR have all represented major advances in dengue diagnosis. However, an appropriate rapid, early and accessible diagnostic method useful both for epidemiological surveillance and clinical diagnosis is still needed. Also, tools that suggest a prognosis allowing for better management are also needed. Finally, laboratory infrastructure, technical expertise and research capacity must be improved in endemic countries in order to positively influence dengue surveillance, clinical case management and the development of new approaches to dengue control.

Dengue: an update

This review is an update of dengue and dengue haemorrhagic fever (DHF) based on international and Cuban experience. We describe the virus characteristics and risk factors for dengue and DHF, and compare incidence and the case fatality rates in endemic regions (southeast Asia, western Pacific, and the Americas). The clinical picture and the pathogenesis of the severe disease are explained. We also discuss the viral, individual, and environmental factors that determine severe disease. Much more research is necessary to clarify these mechanisms. Also reviewed are methods for viral isolation and the serological, immunohistochemical, and molecular methods applied in the diagnosis of the disease. We describe the status of vaccine development and emphasise that the only alternative that we have today to control the disease is through control of its vector Aedes aegypti.

Molecular techniques should not now replace cell culture in diagnostic virology laboratories

The value of molecular techniques for virology is not in dispute; the issue debated here is whether or not to abandon virus isolation altogether. Modern clinical virology relies on rapid virus detection for timely infection control and antiviral therapy. The role of virus isolation, inevitably a slower process as it involves replication in cell cultures, is most significant in providing epidemiological data, in the diagnosis of new or unexpected infection, and in yielding infectious virus for further study. Examples include identification of enterovirus serotypes in outbreaks, diagnosis of atypical virus infections, and provision of virus isolates for phenotypic antiviral susceptibility assays. Many viruses can be detected after overnight culture using the centrifugation-enhanced (shell vial) technique. In contrast to this established track record, the commercial development of molecular assays has been concentrated on blood-borne viruses, and standardisation of procedures for other viruses is lacking. Accreditation of molecular techniques is just beginning, and few external quality assurance schemes are available yet. In my view, it is premature to abandon routine virus isolation, although as molecular diagnosis expands, the facilities for cell culture and isolation work may become more centralised to retain expertise and to provide the range and quality of service required.