Combinatorial computational approaches to identify tetracycline derivatives as flavivirus inhibitors

Limited structural information of drug targets, cellular toxicity possessed by lead compounds, and large amounts of potential leads are the major issues facing the design-oriented approach of discovering new leads. In an attempt to tackle these issues, we have developed a process of virtual screening based on the observation that conformational rearrangements of the dengue virus envelope protein are essential for the mediation of viral entry into host cells via membrane fusion. Screening was based solely on the structural information of the Dengue virus envelope protein and was focused on a target site that is presumably important for the conformational rearrangements necessary for viral entry. To circumvent the issue of lead compound toxicity, we performed screening based on molecular docking using structural databases of medical compounds. To enhance the identification of hits, we further categorized and selected candidates according to their novel structural characteristics. Finally, the selected candidates were subjected to a biological validation assay to assess inhibition of Dengue virus propagation in mammalian host cells using a plaque formation assay. Among the 10 compounds examined, rolitetracycline and doxycycline significantly inhibited plaque formation, demonstrating their inhibitory effect on dengue virus propagation. Both compounds were tetracycline derivatives with IC₅₀s estimated to be 67.1 µM and 55.6 µM, respectively. Their docked conformations displayed common hydrophobic interactions with critical residues that affected membrane fusion during viral entry. These interactions will therefore position the tetracyclic ring moieties of both inhibitors to bind firmly to the target and, subsequently, disrupt conformational rearrangement and block viral entry. This process can be applied to other drug targets in which conformational rearrangement is critical to function.

Survival and replication of dengue-2 virus in diapausing eggs of Aedes albopictus (Diptera: Culicidae)

Survival and replication of dengue-2 virus (family Flaviviridae, genus Flavivirus, DENV-2) was determined in diapausing eggs of Aedes albopictus (Skuse) (Diptera: Culicidae) to evaluate the importance of this mechanism for viral maintenance during adverse climatic conditions. Infected and uninfected eggs of Ae. albopictus were induced to diapause under low temperature and short photoperiod. Virus was detected by reverse transcription-polymerase chain reaction and isolated in C6/36 cells from both diapausing eggs and nondiapausing eggs. Nucleic acid hybridization was used to monitor viral replication in diapausing eggs. DENV-2 might survive in infected diapausing eggs in a relatively quiescent status based on the absence of areplicative intermediate RNA. In contrast, the viral replicative intermediate RNA along with the replicative form RNA was detected in nondiapausing eggs. It seemed that the virus replicated more actively in nondiapausing eggs than in diapausing eggs. Infected diapausing eggs may play an important role in the maintenance of DENV during adverse climatic conditions in nature.

Antibody‐Dependent Cellular Cytotoxicity Mediated by Plasma Obtained before Secondary Dengue Virus Infections: Potential Involvement in Early Control of Viral Replication

BACKGROUND

Preexisting dengue virus (DV)-specific antibodies from prior heterologous DV infection may have several effects in secondary DV infection. These antibodies may mediate protective effects by means of antibody-dependent cellular cytotoxicity (ADCC), in which virus-specific antibodies bind to the surface of heterologous DV-infected cells and mediate natural killer cell lysis. In the present study, we examined the ability of plasma obtained before secondary DV infection to induce ADCC of DV-infected cells.

METHODS

Plasma samples were obtained before DV2 or DV3 infection in a prospective cohort study of Thai schoolchildren. The ADCC activity in the plasma samples was measured by (51)Cr-release assay, using persistently DV2- or DV3-infected Raji cells as targets.

RESULTS

ADCC activity in plasma obtained before secondary infection directly correlated with neutralizing antibody titers, anti-DV immunoglobulin G1 levels, and a multitypic 50% plaque reduction neutralization test pattern. ADCC activity in pre-secondary DV3 infection plasma samples inversely correlated with plasma viremia levels, but no such correlation was seen in pre-secondary DV2 infection plasma samples. ADCC activity did not correlate with disease severity in subsequent secondary DV2 or DV3 infection but was lowest in plasma from patients with dengue hemorrhagic fever due to secondary DV3 infection.

CONCLUSIONS

ADCC may contribute to the early control of secondary DV3 viremia in vivo.

Attenuated dengue 2 viruses with deletions in capsid protein derived from an infectious full-length cDNA clone

A full-length cDNA clone (pD212) of dengue virus type 2 isolated in China (DEN2-43) was constructed. Based on this, we constructed several mutants with deletions in capsid protein C using fusion PCR. These deletions removed part or almost all of the internal stretch of hydrophobic amino acid residues that is probably involved in virion assembly. We thus obtained viable mutant viruses. The propagation capacity of the mutant viruses in cell culture was impaired in parallel with the increasing size of the deletion, and the infectivity of mutant C(Delta42-59), from which all of helix III of capsid protein C was removed, was completely abolished. More importantly, the mutant viruses were highly attenuated in suckling mice but induced high levels of antibodies in adult mice. This study indicates that the structural and functional flexibility of capsid protein C make it a candidate target for the attenuation of dengue virus, which could open a promising new avenue for the development of live attenuated dengue vaccines.

Susceptibility of mouse macrophage J774 to dengue virus infection

The aim of this study was to investigate whether the J774 mouse macrophage cell line could be used as an in vitro model for dengue virus infection (DENV). After 3 days, infection in J774 cells was assessed by detecting dengue virus non-structural protein 1 (NSP-1) production either by dot blot or indirect immunofluorescence assay (IFA) of saponine-permeabilized J774 cells and then confirmed by RT-PCR (171 bp product, corresponding to the DENV-2 core). Based on the presence of NSP-1 in infected but not in non-infected cells by both IFA and dot blot, as well as the amplification of a 171-bp DENV-2-specific RT-PCR product exclusively in the infected cells, the J774 cell line was found to be permissive for dengue virus infection. As far as we know, this is the first report that the J774 mouse macrophage cell line is infected with dengue virus and, thus, that it can be used as an alternative in vitro model for dengue virus infection studies. This finding could help to further elucidate the mechanisms involved in dengue virus infection and pathogenesis.

Construction and biological properties of yellow fever 17D/dengue type 1 recombinant virus

Dengue virus, a mosquito-borne flavivirus, is one of the most formidable public health threats in tropical and subtropical regions. As yet, there is no licensed vaccine to protect against the disease. A chimeric yellow fever (YF) 17D/dengue (DEN) type 1 virus was constructed by replacing the pre-membrane and envelope genes of YF 17D virus with those from DEN 1 VeMir95 virus, a Venezuelan isolate. The chimeric YF 17D/DEN 1 VeMir95 virus was regenerated from full-length infectious clones stably propagated in Escherichia coli by transfection of Vero cells with in vitro transcribed RNA. The chimeric virus proliferated efficiently in Vero cells ( approximately 6.6 log(10) plaque-forming units/ml). The chimeric virus was not neurovirulent to 3-week-old Swiss Webster mice inoculated by the intracerebral route, in contrast to the YF 17DD vaccine strain that was lethal for 90% of the mice. The YF 17D/DEN 1 virus at Passage 6 was more attenuated for rhesus monkeys than the YF 17DD commercial vaccine after intracerebral inoculation according to the standard neurovirulence test. This virus is a potential candidate to be included in a tetravalent DEN vaccine formulation. The availability of the cloned cDNA allows further structure/function studies on the viral envelope.

A prospective clinical study on the use of reverse transcription-polymerase chain reaction for the early diagnosis of Dengue fever

Laboratory testing for dengue virus is used to confirm the diagnosis of dengue virus infection and to differentiate dengue from other febrile tropical illnesses. There are few data on the clinical use of reverse transcription-polymerase chain reaction (RT-PCR) for diagnosis of dengue virus infection. We prospectively evaluated 121 consecutive patients with possible dengue who had samples submitted for RT-PCR, IgM serology, and virus culture. Results were compared with the final discharge diagnosis. Semi-nested RT-PCR was performed using genus- and serotype-specific NS3 consensus primers. Results of 112 patients were available for the final analysis. The RT-PCR was positive in 40 of 62 patients with dengue. Patients who were RT-PCR-positive alone showed a mean of 4.4 days to RT-PCR positivity compared with 5.9 days in patients who were RT-PCR-negative and IgM serology-positive (P = 0.03, Mann-Whitney U-test). The sensitivity, specificity, negative predictive value, and positive predictive value were 70, 100, 84, and 100%, respectively, for samples analyzed within 5 days of illness onset. The RT-PCR also provided epidemiological data regarding the prevailing dengue virus serotypes: 25 with Den-2, eight with Den-3, and seven with Den-1 infection. We propose an algorithm of dengue testing that uses RT-PCR within 5 days of illness onset, whereas IgM capture enzyme-linked immunosorbent assay is preferred for those presenting later.

A novel tetraspanin C189 upregulated in C6/36 mosquito cells following dengue 2 virus infection

Dengue (Den) viruses cause apoptosis in mammalian cells, but usually result in high progeny yields without evident damage in mosquito cells. By using subtractive hybridization, 13 potentially virus-induced genes were selected in Den-2 virus-infected Aedes albopictus C6/36 cells. Based on semi-quantitative and real-time RT-PCR, one novel gene, named C189, was significantly upregulated in infected C6/36 cells. Its full-length of 678 nucleotides (nt) was determined by a combination of 5'- and 3'-RACE products. After alignment, C189 was classified as a member of the tetraspanin superfamily that typically has 2 short cytoplasmic sequences, 4 transmembrane domains, as well as small and large extracellular regions (EC1 and EC2). It contains the hallmark CCG motif in the EC2 region and additional 17 conserved nucleotides as do other tetraspanins. C189 was not upregulated by inoculation of UV-inactivated Den-2 virus to C6/36 cells. This suggests that tetraspanin upregulation is not related to virus binding to the cell surface, and that C189 does not function as a receptor for dengue virus entry. On the other hand, overexpression of C189 was concurrent with viral proteins, targeting the plasma membrane of C6/36 cells infected with Den-2 virus. It is presumably beneficial or essential for cell-to-cell spread of the virus due to the role of tetraspanins demonstrated in intercellular adhesion.

Development of real-time reverse transcriptase PCR assays to detect and serotype dengue viruses

Serotyping dengue virus (DENV) from suspect human specimens is crucial for developing sound epidemiological control measurements early in the transmission season and for effective patient management. We modified DENV consensus D1 (mD1) and serotype-specific TS2 (mTS2) and redesigned serotype-specific TS1 (rTS1) and TS4 (rTS4) as described previously in the conventional capsid and premembrane gene (C-prM) protocol (R. S. Lanciotti, C. H. Calisher, D. J. Gubler, G.-J. Chang, A. V. Vorndam, J. Clin. Microbiol. 30:545-551, 1992). In addition, we designed two new sets of amplimers and probes, located at nonstructural protein 5 (NS5) and the 3' noncoding region (3'NC) of DENV. The NS5 protocol utilizes two flaviviral consensus outer amplimers (mFU1 and CFD2) and four dengue virus serotype-specific TaqMan fluorogenic probes. The 3'NC protocol uses two DENV consensus amplimers, DC10418 and CDC10564. The conventional gel-based, heminested detection method was adapted for the C-prM protocol for detecting and serotyping dengue viruses. In addition, we developed the real-time SYBR green I and postamplification melting temperature curve analysis for the mD1/TS and 3'NC protocols using identical amplification conditions. The NS5 amplimer/probe set was formulated as a one-tube, multiplex, real-time reverse transcriptase PCR for serotype identification. Three sets of amplimers and probes were verified for their specificity in tests with yellow fever, Japanese encephalitis, St. Louis encephalitis, and West Nile viruses; optimized against 109 DENV strains; and validated for detection of the virus in sera from two different panels of acute-phase human dengue serum specimens and one panel of virus isolates from dengue patients' serum specimens. Clinical evaluation by two separate laboratories indicated that the C-prM was more sensitive (100%) than the NS5 (91%) or the 3'NC (91%) protocol.

Murine model for dengue virus-induced lethal disease with increased vascular permeability

Lack of an appropriate animal model for dengue virus (DEN), which causes dengue fever and dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), has impeded characterization of the mechanisms underlying the disease pathogenesis. The cardinal feature of DHF/DSS, the severe form of DEN infection, is increased vascular permeability. To develop a murine model that is more relevant to DHF/DSS, a novel DEN strain, D2S10, was generated by alternately passaging a non-mouse-adapted DEN strain between mosquito cells and mice, thereby mimicking the natural transmission cycle of the virus between mosquitoes and humans. After infection with D2S10, mice lacking interferon receptors died early without manifesting signs of paralysis, carried infectious virus in both non-neuronal and neuronal tissues, and exhibited signs of increased vascular permeability. In contrast, mice infected with the parental DEN strain developed paralysis at late times after infection, contained detectable levels of virus only in the central nervous system, and displayed normal vascular permeability. In the mice infected with D2S10, but not the parental DEN strain, significant levels of serum tumor necrosis factor alpha (TNF-alpha) were produced, and the neutralization of TNF-alpha activity prevented early death of D2S10-infected mice. Sequence analysis comparing D2S10 to its parental strain implicated a conserved region of amino acid residues in the envelope protein as a possible source for the D2S10 phenotype. These results demonstrate that D2S10 causes a more relevant disease in mice and that TNF-alpha may be one of several key mediators of severe DEN-induced disease in mice. This report represents a significant advance in animal models for severe DEN disease, and it begins to provide mechanistic insights into DEN-induced disease in vivo.

Differential enhancement of dengue virus immune complex infectivity mediated by signaling-competent and signaling-incompetent human Fcgamma RIA (CD64) or FcgammaRIIA (CD32)

Fcgamma receptor (FcgammaR)-mediated entry of infectious dengue virus immune complexes into monocytes/macrophages is hypothesized to be a key event in the pathogenesis of complicated dengue fever. FcgammaRIA (CD64) and FcgammaRIIA (CD32), which predominate on the surface of such dengue virus-permissive cells, were compared for their influence on the infectivity of dengue 2 virus immune complexes formed with human dengue virus antibodies. A signaling immunoreceptor tyrosine-based activation motif (ITAM) incorporated into the accessory gamma-chain subunit that associates with FcgammaRIA and constitutively in FcgammaRIIA is required for phagocytosis mediated by these receptors. To determine whether FcgammaRIA and FcgammaRIIA activation functions are also required for internalization of infectious dengue virus immune complexes, we generated native and signaling-incompetent versions of each receptor by site-directed mutagenesis of ITAM tyrosine residues. Plasmids designed to express these receptors were transfected into COS-7 cells, and dengue virus replication was measured by plaque assay and flow cytometry. We found that both receptors mediated enhanced dengue virus immune complex infectivity but that FcgammaRIIA appeared to do so far more effectively. Abrogation of FcgammaRIA signaling competency, either by expression without gamma-chain or by coexpression with gamma-chain mutants, was associated with significant impairment of phagocytosis and of dengue virus immune complex infectivity. Abrogation of FcgammaRIIA signaling competency was also associated with equally impaired phagocytosis but had no discernible effect on dengue virus immune complex infectivity. These findings point to fundamental differences between FcgammaRIA and FcgammaRIIA with respect to their immune-enhancing capabilities and suggest that different mechanisms of dengue virus immune complex internalization may operate between these FcgammaRs.

Growth characteristics of ChimeriVax-Den vaccine viruses in Aedes aegypti and Aedes albopictus from Thailand

Four chimeric yellow fever (YF) 17D-dengue (DEN) candidate vaccine viruses (ChimeriVax-DEN; Acambis, Cambridge, MA) were characterized in Aedes aegypti and Ae. albopictus mosquitoes collected from Thailand. The four vaccine viruses contained the relevant prM and E genes of wild-type dengue viruses (DENV; serotypes 1-4) substituted for the equivalent genes in the YF vaccine virus (17D) backbone. Each chimera conferred protection against the homologous DENV serotype; a tetravalent mix of all four chimeras stimulates an immune response against all serotypes. Field-collected mosquitoes from Thailand were fed on blood containing each of the viruses under study and held 21 days after infection. Infection and dissemination rates were based on antigen detection in the body or head tissues, respectively. All four wild-type DENV serotypes infected and disseminated, but the candidate vaccine viruses were highly attenuated in mosquitoes with respect to infection and especially with respect to dissemination. Considering the low level viremias anticipated in humans vaccinated with these viruses, it is predicted that the risks of infection and transmission by mosquitoes in nature is minimal.

Threshold conditions for a non-autonomous epidemic system describing the population dynamics of dengue

A non-autonomous dynamical system, in which the seasonal variation of a mosquito vector population is modeled, is proposed to investigate dengue overwintering. A time-dependent threshold, R(t), is deduced such that when its yearly average, denoted by R, is less than 1, the disease does not invade the populations and when R is greater than 1 it does. By not invading the population we mean that the number of infected individuals always decrease in subsequent seasons of transmission. Using the same threshold, all the qualitative features of the resulting epidemic can be understood. Our model suggests that trans-ovarial infection in the mosquitoes facilitates dengue overwintering. We also explain the delay between the peak in the mosquitoes population and the peak in dengue cases.

Role of T cells, cytokines and antibody in dengue fever and dengue haemorrhagic fever

Dengue infections are a major cause of morbidity and mortality in the tropical and sub-tropical regions of the world. There is no vaccine for dengue and also there are no anti-viral drugs to treat the infection. Some patients, typically those experiencing a secondary infection with a different dengue serotype, may progress from an acute febrile disease to the more severe forms of disease, dengue haemorrhagic fever and dengue shock syndrome. Here we discuss the significant immunopathological component to severe disease and how T cells, cytokines and cross-reactive antibody combine to contribute to the progression to dengue haemorrhagic fever. These events are thought to lead to vascular leakage, the signature event in dengue haemorrhagic fever, and are addressed in this review by incorporating the concept of heterologous T cell immunity. The need for effective measures against dengue and dengue-related illness is clear. We propose that drugs against dengue virus, or the symptoms of severe dengue disease, are a viable goal.

Folk knowledge about dengue mosquitoes and contributions of health belief model in dengue control promotion in Northeast Thailand

The health belief model (HBM) has been adopted as the principal theory for health education and communication for dengue haemorrhagic fever (DHF) prevention and control in Thailand. The HBM focuses on persuading people to acknowledge their vulnerability and susceptibility to DHF, and the benefits of undertaking dengue larval control in household water containers. This study was undertaken in Khon Kaen province to investigate folk knowledge and beliefs about dengue mosquitoes and larval control campaigns and relating these to the theoretical components of HBM. Findings from this study indicate that health education messages can raise awareness during an outbreak but do not ensure sustained larval control practices. Several barriers are identified, including insufficient control agents, inadequate knowledge of control methods, and incompatibility of control practices with people's beliefs. The barriers prevail over the benefits of recommended larval control practices. In developing health education messages, consideration should go beyond the HBM and focus on control methods that are compatible with the socio-cultural environment in which control practices are being encouraged.

Dengue prevention and 35 years of vector control in Singapore

A vector control program must be based on epidemiologic and entomologic data.

After a 15-year period of low incidence, dengue has reemerged in Singapore in the past decade. We identify potential causes of this resurgence. A combination of lowered herd immunity, virus transmission outside the home, an increase in the age of infection, and the adoption of a case-reactive approach to vector control contribute to the increased dengue incidence. Singapore's experience with dengue indicates that prevention efforts may not be sustainable. For renewed success, Singapore needs to return to a vector control program that is based on carefully collected entomologic and epidemiologic data. Singapore's taking on a leadership role in strengthening disease surveillance and control in Southeast Asia may also be useful in reducing virus importation.

A stochastic population dynamics model for Aedes aegypti: formulation and application to a city with temperate climate

Aedes aegypti is the main vector for dengue and urban yellow fever. It is extended around the world not only in the tropical regions but also beyond them, reaching temperate climates. Because of its importance as a vector of deadly diseases, the significance of its distribution in urban areas and the possibility of breeding in laboratory facilities, Aedes aegypti is one of the best-known mosquitoes. In this work the biology of Aedes aegypti is incorporated into the framework of a stochastic population dynamics model able to handle seasonal and total extinction as well as endemic situations. The model incorporates explicitly the dependence with temperature. The ecological parameters of the model are tuned to the present populations of Aedes aegypti in Buenos Aires city, which is at the border of the present day geographical distribution in South America. Temperature thresholds for the mosquito survival are computed as a function of average yearly temperature and seasonal variation as well as breeding site availability. The stochastic analysis suggests that the southern limit of Aedes aegypti distribution in South America is close to the 15 degrees C average yearly isotherm, which accounts for the historical and current distribution better than the traditional criterion of the winter (July) 10 degrees C isotherm.

Serotype-specific differences in clinical manifestations of dengue

Dengue, the most prevalent arthropod-borne viral disease of humans, is caused by four serotypes of dengue virus (DENV 1-4). Although all four DENV serotypes cause a range of illness, defining precisely which clinical characteristics are associated with the distinct serotypes has been elusive. A cross-sectional study was conducted on 984 and 313 hospitalized children with confirmed DENV infections during two time periods, respectively, in the same hospitals in Nicaragua: a 3-year period (1999-2001) when DENV-2 accounted for 96% of the viruses identified, and the 2003 dengue season when DENV-1 predominated (87% of identified serotypes). When the two periods were compared, more shock (OR 1.91, 95% CI 1.35-2.71) and internal hemorrhage (OR 2.05, CI 1.16-3.78) were observed in the period when DENV-2 predominated, whereas increased vascular permeability was associated to a greater degree with the DENV-1 period (OR 2.36, CI 1.80-3.09). Compared with the DENV-2 period, the DENV-1 season was associated with more hospitalized primary dengue cases (OR 3.86, CI 2.72-5.48) and more primary DENV infections with severe manifestations (OR 2.93, CI 2.00-4.28). These findings provide new data to characterize the pathogenic potential of distinct DENV serotypes in human populations.

Growth and production of the dengue virus in C6/36 cells and identification of a laminin-binding protein as a candidate serotype 3 and 4 receptor protein

OBJECTIVES

Although dengue is one of the most common mosquito-borne viral diseases, few studies have investigated the relationship between the dengue virus and mosquito cells, and this study sought to describe the binding and propagation of the dengue viruses in C6/36 cells.

METHODS

The internalization and production of the dengue virus was assayed by standard plaque assay methodologies, while dengue virus receptor proteins were examined by a virus overlay protein-binding assay and candidate gene analysis coupled with virus inhibition studies.

RESULTS

All four serotypes were internalized linearly, and de novo virus production occurred 14-19 h postinfection. Virus overlay protein-binding assay identified a band of 50 kDa for dengue serotypes 2, 3 and 4 which comigrated with a protein that reacts with antibodies directed against the human 37/67-kDa high-affinity laminin receptor. Both antibodies directed against the human 37/67-kDa high-affinity laminin receptor protein and soluble laminin inhibited the binding and internalization of serotypes 3 and 4, but not serotypes 1 and 2.

CONCLUSIONS

The results suggest that multiple receptors may be used by the dengue virus to enter into insect cells, and that one of these proteins may be a laminin-binding protein.

Quantitation of flaviviruses by fluorescent focus assay

An indirect immunofluorescence assay for quantitation of flaviviruses was developed as an alternative to the standard plaque assay. The assay was validated with West Nile virus (WNV), St. Louis encephalitis virus (SLEV), and Dengue virus (DENV) types 1-4. Vero cells were plated in 8-well chamber slides, and infected with 10-fold serial dilutions of virus. About 1-3 days after infection, cells were fixed, incubated with specific monoclonal antibody, and stained with a secondary antibody labeled with a fluorescent tag. Fluorescent foci of infection were observed and counted using a fluorescence microscope, and viral titers were calculated as fluorescent focus units (FFU) per ml. The optimal time for performing the fluorescent focus assay (FFA) on Vero cells was 24 h for WNV, and 48 h for SLEV and the four DENV serotypes. In contrast, the time required to complete a standard Vero cell plaque assay for these viruses range from 3 days for WNV to 11 days for DENV-1. Thus, the FFA method of virus titration is useful for viruses whose plaques develop slowly. In addition, these viruses can be quantitated by FFA on a mosquito cell line (C6/36), which does not support plaque formation. The FFA for flaviviruses was validated for accuracy, precision, specificity, and robustness of the assay.

Sensitivity of Aedes albopictus C6/36 cells line for the detection and infectivity titration of dengue virus

Plaque assay procedure was carried out to determine the infectivity titration of dengue virus using Aedes albopictus C6/36 mosquito cell line. Cells were seeded in 6 wells plates and incubated until monolayer C6/36 cell lines were formed. Each well was exposed to a different dilution of dengue infected culture fluid, followed by addition of first and second overlay medium. Cells were observed under an inverted microscope and plaque staining was carried out. The results showed that countable plaques were not achieved and plaques formed were restricted to the central section due to the significant partial lysis of the C6/36 cells in the plates. However, the plaque assay technique using C6/36 cell line reported here appears to be promising and merits further detailed studies.

Dengue typing assay based on real-time PCR using SYBR Green I

Typing of dengue virus is crucial for the epidemiology and pathogenesis of dengue virus infection. Hence, highly sensitive and accurate diagnostic tools are essential. The purpose of this study was to identify all four types of dengue virus based on the 3'-untranslated region of the virus by melting curve analysis and real-time PCR using SYBR Green I. The types obtained by this method were compared with the results of direct sequencing of 39 serum or plasma samples of patients with clinical dengue infection that included a positive tourniquet test, thrombocytopenia and positive dengue IgM antibody. The accuracy of typing by melting curve analysis was 97.4%. In conclusion, real-time PCR and melting curve analysis using one single-primer pair were shown to be highly efficient for clear detection and typing of dengue virus in clinical specimens. This method therefore represents a simple, sensitive, specific, rapid and economic method, which will be essential for epidemiological studies of dengue virus infection.

Inhibition of dengue virus translation and RNA synthesis by a morpholino oligomer targeted to the top of the terminal 3' stem-loop structure

Dengue virus (DEN) is a major public health problem worldwide and causes a spectrum of diseases, for which no antiviral treatments exist. Peptide-conjugated phosphorodiamidate morpholino oligomers (P-PMOs) complementary to the DEN 5' stem-loop (5'SL) and to the DEN 3' cyclization sequence (3'CS) inhibit DEN replication, presumably by blocking critical RNA-RNA or RNA-protein interactions involved in viral translation and/or RNA synthesis. Here, a third P-PMO, complementary to the top of the 3' stem-loop (3'SLT), inhibited DEN replication in BHK cells. Using a novel DEN2 reporter replicon and a DEN2 reporter mRNA, we determined that the 5'SL P-PMO inhibited viral translation, the 3'CS P-PMO blocked viral RNA synthesis but not viral translation, and the 3'SLT P-PMO inhibited both viral translation and RNA synthesis. These results show that the 3'CS and the 3'SL domains regulate DEN translation and RNA synthesis and further demonstrate that P-PMOs are potentially useful as antiviral agents.

Molecular epidemiology of dengue 2 viruses in the Philippines: genotype shift and local evolution

The pre-membrane (prM) and envelope (E) genes of 41 viruses isolated from dengue fever (DF), dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS) patients from 1995 to 2002 were sequenced to determine the genetic variability of dengue 2 (DENV 2) viruses in the Philippines. The envelope sequence data were compared with a global sample of DENV 2 obtained from GenBank. Phylogenetic analysis revealed that two distinct genotypes, Asian 2 and Cosmopolitan, are currently circulating locally, each with the potential to cause severe hemorrhagic disease. After the initial isolation in 1998, the Cosmopolitan genotype has gradually and effectively replaced Asian genotype 2 in the Philippines. Members of this genotype were closely related to viruses from Australia, Singapore, and Thailand.

Capsid-targeted viral inactivation can destroy dengue 2 virus from within in vitro

Capsid-targeted viral inactivation (CTVI) has emerged as a conceptually powerful antiviral strategy that exploits viral structural proteins to target a destructive enzyme specifically into progeny virions. We have recently demonstrated the principle of CTVI against dengue virus infection and observed a modest therapeutic effect in vitro (Arch Virol 2005, 150: 659-669). Here we tested a prophylactic model of CTVI, in which mammalian cells stably expressing the dengue 2 virus capsid protein fused to a nuclease were infected with dengue virus and determined the effects on progeny virion infectivity. CTVI efficiently destroyed dengue 2 virus from within and decreased the infectious titers by 10(3)- to 10(4)-fold, suggesting that CTVI has potential in the prophylactic application for dengue virus infection.