Peptide Biomarkers for the Diagnosis of Dengue Infection

In a world with an increasing population at risk of exposure to arthropod-borne flaviviruses, access to timely and accurate diagnostic tests would impact profoundly on the management of cases. Twenty peptides previously identified using a flavivirus proteome-wide microarray were evaluated to determine their discriminatory potential to detect dengue virus (DENV) infection. This included nine peptides recognized by IgM antibodies (PM peptides) and 11 peptides recognized by IgG antibodies (PG peptides). A bead-based multiplex peptide immunoassay (MPIA) using the Luminex technology was set-up to determine Ab binding levels to each of these peptides in a panel of 323 carefully selected human serum samples. Sera are derived from individuals either infected with different viruses, namely, the four DENV serotypes, Zika virus (ZIKV), yellow fever virus (YFV), chikungunya virus (CHIKV), West Nile virus (WNV) and Human immunodeficiency virus (HIV), or receiving vaccination against YFV, tick-borne encephalitis (TBEV), and Japanese encephalitis virus (JEV). Additionally, a set of healthy controls were included. We targeted a minimum specificity of 80% for all the analysis. The PG-9 peptide had the best sensitivity (73%) when testing DENV sera from acute patients (A-DENV; <8 days since symptom onset). With sera from convalescent DENV patients (C-DENV; >10 days since symptom onset) the FPG-1 peptide was the best seromarker with a sensitivity of 86%. When combining all A-DENV and C-DENV samples, peptides PM-22 and FPG-1 had the best-diagnostic performance with a sensitivity of 60 and 61.1%, and areas under the curve (AUC) of 0.7865 and 0.8131, respectively. A Random forest (RF) algorithm was used to select the best combination of peptides to classify DENV infection at a targeted specificity >80%. The best RF model for PM peptides that included A-DENV and C-DENV samples, reached a sensitivity of 72.3%, while for PG peptides, the best RF models for A-DENV only, C-DENV only and A-DENV + C-DENV reached a sensitivity of 88.9%, 89.1%, and 88.3%, respectively. In conclusion, the combination of multiple peptides constitutes a founding set of seromarkers for the discrimination of DENV infected individuals from other flavivirus infections.

Impact of COVID-19 in patients with concurrent co-infections: A systematic review and meta-analyses

The burden and impact of secondary superadded infections in critically ill coronavirus disease 2019 (COVID-19) patients is widely acknowledged. However, there is a dearth of information regarding the impact of COVID-19 in patients with tuberculosis, HIV, chronic hepatitis, and other concurrent infections. This review was conducted to evaluate the consequence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection in patients with concurrent co-infections based on the publications reported to date. An extensive comprehensive screening was conducted using electronic databases up to 3rd September 2020 after obtaining registration with PROSPERO (CRD420202064800). The observational studies or interventional studies in English, evaluating the impact of SARS-CoV-2 in patients with concurrent infections are included for the meta-analyses. Our search retrieved 20 studies, with a total of 205,702 patients. Patients with tuberculosis (RR = 2.10; 95% CI, 1.75-2.51; I²  = 0%), influenza (RR = 2.04; 95% CI, 0.15-28.25, I²  = 99%) have an increased risk of mortality during a co-infection with SARS-CoV-2. No significant impact is found in people living with HIV (RR = 0.99; 95% CI, 0.82-1.19; I²  = 30%), Chronic hepatitis (RR = 1.15; 95% CI, 0.73-1.81; I²  = 10%). Several countries (Brazil, Paraguay, Argentina, Peru, Colombia, and Singapore) are on the verge of a dengue co epidemic (cumulative 878,496 and 5,028,380 cases of dengue and COVID-19 respectively). The impact of COVID-19 in patients of concurrent infections with either tuberculosis or influenza is detrimental. The clinical outcomes of COVID-19 in HIV or chronic hepatitis patients are comparable to COVID-19 patients without these concurrent infections.

DEN-IM: dengue virus genotyping from amplicon and shotgun metagenomic sequencing

Dengue virus (DENV) represents a public health threat and economic burden in affected countries. The availability of genomic data is key to understanding viral evolution and dynamics, supporting improved control strategies. Currently, the use of high-throughput sequencing (HTS) technologies, which can be applied both directly to patient samples (shotgun metagenomics) and to PCR-amplified viral sequences (amplicon sequencing), is potentially the most informative approach to monitor viral dissemination and genetic diversity by providing, in a single methodological step, identification and characterization of the whole viral genome at the nucleotide level. Despite many advantages, these technologies require bioinformatics expertise and appropriate infrastructure for the analysis and interpretation of the resulting data. In addition, the many software solutions available can hamper the reproducibility and comparison of results. Here we present DEN-IM, a one-stop, user-friendly, containerized and reproducible workflow for the analysis of DENV short-read sequencing data from both amplicon and shotgun metagenomics approaches. It is able to infer the DENV coding sequence (CDS), identify the serotype and genotype, and generate a phylogenetic tree. It can easily be run on any UNIX-like system, from local machines to high-performance computing clusters, performing a comprehensive analysis without the requirement for extensive bioinformatics expertise. Using DEN-IM, we successfully analysed two types of DENV datasets. The first comprised 25 shotgun metagenomic sequencing samples from patients with variable serotypes and genotypes, including an in vitro spiked sample containing the four known serotypes. The second consisted of 106 paired-end and 76 single-end amplicon sequences of DENV 3 genotype III and DENV 1 genotype I, respectively, where DEN-IM allowed detection of the intra-genotype diversity. The DEN-IM workflow, parameters and execution configuration files, and documentation are freely available at https://github.com/B-UMMI/DEN-IM).

Dengue in Taiwan: Pointing the finger at Aedes aegypti

In this issue of the Biomedical Journal we explore the history of dengue infection in Taiwan and what current trends have to say about the vector responsible for transmitting the disease on the island. We focus on original research reporting the development of a new perfusion bioreactor to engineer bone from human cord blood stem cells. Finally, we look at trends in osteoporosis in Taiwan and how they highlight the success of public health campaigns.

Pathogen-specific leptospiral proteins in urine of patients with febrile illness aids in differential diagnosis of leptospirosis from dengue

Leptospirosis and dengue are two commonly seen infectious diseases of the tropics. Differential diagnosis of leptospirosis from dengue fever is often difficult due to overlapping clinical symptoms and lack of economically viable and easy-to-perform laboratory tests. The gold standard for diagnosis is the microscopic agglutination test (MAT). In this study, the diagnostic potential of screening for pathogen-specific leptospiral antigens in urine samples is presented as a non-invasive method of disease diagnosis. In a study group of 40 patients, the serum was tested for anti-leptospiral antibodies by MAT and enzyme-linked immunosorbent assay (ELISA). Urine of these patients was screened for leptospiral antigens by ELISA using specific antibodies against LipL32, LipL41, Fla1, HbpA and sphingomyelinase. Group I patients (n = 23) were classified as leptospirosis-positive based on MAT and high titres of circulating IgM-specific anti-leptospiral antibodies. All of these patients excreted all five leptospiral antigens in the urine. The 17 MAT-negative cases included six patients with pyrexia of unknown origin (PUO; Group II) and 11 confirmed dengue patients (Group III). The latter tested negative for both serum anti-leptospiral antibodies and urinary leptospiral antigens. A salient outcome of this study was highlighting the usefulness of screening for urinary leptospiral antigens in disease diagnosis, as their presence confirmed leptospiral aetiology in two PUO patients. Immunoblots of urinary antigens identified well-defined bands corresponding to LipL32, HbpA and sphingomyelinase; the significance of the 42- and 58-kDa sphingomyelinase bands is discussed.

Lipids and Pathogen Blocking by Wolbachia

Mosquito-borne viruses are major human pathogens. Introducing Wolbachia into mosquitoes could reduce disease burdens because these bacteria block virus transmission. How Wolbachia does this is unclear, but new data show that modulation of host-cell lipids is critical.

Comparison of Stable and Transient Wolbachia Infection Models in Aedes aegypti to Block Dengue and West Nile Viruses

Pathogen replication and transmission in Wolbachia infected insects are currently studied using three Wolbachia infection systems: naturally infected Wolbachia hosts, hosts transinfected with Wolbachia (stably maintained and inherited infections) and hosts transiently infected with Wolbachia. All three systems have been used to test the effect of Wolbachia on mosquito transmitted pathogens such as dengue virus (DENV), West Nile virus (WNV) and Plasmodium. From these studies it is becoming increasingly clear that the interaction between a particular pathogen and Wolbachia is heavily influenced by the host-Wolbachia interaction and the model of infection. In particular, there is some evidence that under very specific conditions, Wolbachia can enhance pathogen infection in some hosts. In this study, we compared the effect of Wolbachia in two infection models (stable transinfected and transiently infected) on the replication, infection- and transmission rates of two flaviviruses, DENV and WNV (Kunjin strain). Our results indicate that Wolbachia had similar blocking effects in both stable and transient models of infection, however, the magnitude of the blocking effect was significantly lower in mosquitoes transiently infected with Wolbachia. More importantly, no evidence was found for any enhancement of either DENV or WNV (Kunjin strain) infection in Ae. aegypti infected with Wolbachia, supporting a role for Wolbachia as an effective and safe means for restricting transmission of these viruses.

Wolbachia is a naturally occurring endosymbiotic bacterium that, when introduced into a naïve mosquito host, has been shown to effectively reduce the replication and transmission of pathogens such as dengue virus, West Nile virus, Chikungunya virus, yellow fever virus and Plasmodium. However, a recent study has indicated that, under certain conditions, transiently infected Wolbachia can enhance West Nile virus infection in Culex tarsalis mosquitoes. We wanted to investigate whether this enhancement effect could also be observed in Aedes aegypti mosquitoes and if so, whether it is specific to the nature of the Wolbachia infection model under study (transient vs stable). We compared the replication and transmission of dengue virus and WNV (Kunjin strain) in Aedes aegypti mosquitoes transiently infected with Wolbachia and mosquitoes stably infected with the identical Wolbachia strain. Contrary to the previous study, our results show no enhancement of replication or transmission for either dengue virus or WNV (Kunjin strain) in mosquitoes transiently or stably infected with Wolbachia.

The effect of virus-blocking Wolbachia on male competitiveness of the dengue vector mosquito, Aedes aegypti

Background

The bacterial endosymbiont Wolbachia blocks the transmission of dengue virus by its vector mosquito Aedes aegypti, and is currently being evaluated for control of dengue outbreaks. Wolbachia induces cytoplasmic incompatibility (CI) that results in the developmental failure of offspring in the cross between Wolbachia-infected males and uninfected females. This increases the relative success of infected females in the population, thereby enhancing the spread of the beneficial bacterium. However, Wolbachia spread via CI will only be feasible if infected males are sufficiently competitive in obtaining a mate under field conditions. We tested the effect of Wolbachia on the competitiveness of A. aegypti males under semi-field conditions.

Methodology/Principal Findings

In a series of experiments we exposed uninfected females to Wolbachia-infected and uninfected males simultaneously. We scored the competitiveness of infected males according to the proportion of females producing non-viable eggs due to incompatibility. We found that infected males were equally successful to uninfected males in securing a mate within experimental tents and semi-field cages. This was true for males infected by the benign wMel Wolbachia strain, but also for males infected by the virulent wMelPop (popcorn) strain. By manipulating male size we found that larger males had a higher success than smaller underfed males in the semi-field cages, regardless of their infection status.

Conclusions/Significance

The results indicate that Wolbachia infection does not reduce the competitiveness of A. aegypti males. Moreover, the body size effect suggests a potential advantage for lab-reared Wolbachia-males during a field release episode, due to their better nutrition and larger size. This may promote Wolbachia spread via CI in wild mosquito populations and underscores its potential use for disease control.

Dengue is a tropical, potentially lethal disease transmitted by mosquitoes. A new control method involves the release of mosquitoes infected by the bacterium Wolbachia that blocks the transmission of the dengue virus to humans. However, possible negative effects of Wolbachia on mosquito reproductive success could substantially slow the spread of this bacterium in mosquito populations, reducing the feasibility of this method. We found that male mosquitoes infected by Wolbachia are equally successful in finding and mating with females within experimental tents and semi-field cages that mimic mosquito natural habitat. Moreover, larger, well-fed mosquitoes were more successful in semi-field cages, suggesting that Wolbachia mosquitoes that are reared in the lab, and are generally larger than wild mosquitoes, might have an advantage during the time they are being released in the field. Hence, in contrast to other control methods (e.g., the use of sterile males or genetically modified mosquitoes), the use of Wolbachia does not seem to compromise male performance, making it a candidate for disease control.

Regulation of arginine methyltransferase 3 by a Wolbachia-induced microRNA in Aedes aegypti and its effect on Wolbachia and dengue virus replication

The gram-negative endosymbiotic bacteria, Wolbachia, have been found to colonize a wide range of invertebrates, including over 40% of insect species. Best known for host reproductive manipulations, some strains of Wolbachia have been shown to reduce the host life span by about 50% and inhibit replication and transmission of dengue virus (DENV) in the mosquito vector, Aedes aegypti. The molecular mechanisms underlying these effects still are not well understood. Our previous studies showed that Wolbachia uses host microRNAs (miRNAs) to manipulate host gene expression for its efficient maintenance and limiting replication of DENV in Ae. aegypti. Protein arginine methyltransferases are structurally and functionally conserved proteins from yeast to human. In mammals, it has been reported that protein arginine methyltransferases such as PRMT1, 5 and 6 could regulate replication of different viruses. Ae. aegypti contains eight members of protein arginine methyltransferases (AaArgM1-8). Here, we show that the wMelPop strain of Wolbachia introduced into Ae. aegypti significantly induces the expression of AaArgM3. Interestingly, we found that Wolbachia uses aae-miR-2940, which is highly upregulated in Wolbachia-infected mosquitoes, to upregulate the expression of AaArgM3. Silencing of AaArgM3 in a mosquito cell line led to a significant reduction in Wolbachia replication, but had no effect on the replication of DENV. These results provide further evidence that Wolbachia uses the host miRNAs to manipulate host gene expression and facilitate colonization in Ae. aegypti mosquito.

Vertical transmission of Key West dengue-1 virus by Aedes aegypti and Aedes albopictus (Diptera: Culicidae) mosquitoes from Florida

Following the 2009 and 2010 dengue-1 (DENV-1) outbreaks in Key West, FL, we used Florida Aedes aegypti (L.) mosquitoes and DENV-1 isolated from Key West in 2010 to test the hypothesis that if the 2009 and 2010 DENV-1 genome sequences are similar, then vertical transmission of DENV-1 from infected Ae. aegypti female mosquitoes to their eggs could have served as an interepidemic reservoir between outbreaks. We also investigated the ability of Florida Aedes albopictus (Skuse) mosquitoes to vertically transmit DENV-1. In addition, we determined the rates of infection and dissemination of these Florida mosquito species for DENV-1 and the effect of DENV-1 infection on oviposition success and number of mosquito eggs laid by females. Vertical transmission of DENV-1 was documented, with rates of 11.11% (2 out of 18) for Ae. albopictus and 8.33% (3 out of 36) for Ae. aegypti. Approximately 93% (111 out of 119) of Ae. aegypti that fed on DENV-1 in blood became infected, and 80% (89 out of 111) of infections were disseminated. Similarly, 93% of Ae. albopictus became infected (53 out of 57), and 85% (45 out of 53) of infections were disseminated. No significant differences were detected in numbers of eggs laid by either species after imbibing DENV-1 in blood, suggesting little cost of infection on number of eggs laid. Our results demonstrate that Florida Ae. aegypti and Ae. albopictus mosquitoes are competent vectors for DENV-1, whose maintenance between the 2009 and 2010 Key West outbreaks may have been facilitated by vertical transmission.

The relative importance of innate immune priming in Wolbachia-mediated dengue interference

The non-virulent Wolbachia strain wMel and the life-shortening strain wMelPop-CLA, both originally from Drosophila melanogaster, have been stably introduced into the mosquito vector of dengue fever, Aedes aegypti. Each of these Wolbachia strains interferes with viral pathogenicity and/or dissemination in both their natural Drosophila host and in their new mosquito host, and it has been suggested that this virus interference may be due to host immune priming by Wolbachia. In order to identify aspects of the mosquito immune response that might underpin virus interference, we used whole-genome microarrays to analyse the transcriptional response of A. aegypti to the wMel and wMelPop-CLA Wolbachia strains. While wMel affected the transcription of far fewer host genes than wMelPop-CLA, both strains activated the expression of some immune genes including anti-microbial peptides, Toll pathway genes and genes involved in melanization. Because the induction of these immune genes might be associated with the very recent introduction of Wolbachia into the mosquito, we also examined the same Wolbachia strains in their original host D. melanogaster. First we demonstrated that when dengue viruses were injected into D. melanogaster, virus accumulation was significantly reduced in the presence of Wolbachia, just as in A. aegypti. Second, when we carried out transcriptional analyses of the same immune genes up-regulated in the new heterologous mosquito host in response to Wolbachia we found no over-expression of these genes in D. melanogaster, infected with either wMel or wMelPop. These results reinforce the idea that the fundamental mechanism involved in viral interference in Drosophila and Aedes is not dependent on the up-regulation of the immune effectors examined, although it cannot be excluded that immune priming in the heterologous mosquito host might enhance the virus interference trait.

Wolbachia pipientis is an inherited intracellular bacterium that is widespread in insects. Because of its ability to interfere with various pathogens such as dengue viruses, nematodes and Plasmodium in insects, it has been proposed as a possible tool to control insect-transmitted disease. Recently, two strains of Wolbachia that interfere with RNA viruses in their natural host, Drosophila melanogaster, were introduced into the naturally uninfected mosquito vector of dengue fever, Aedes aegypti. As in their natural host, those two strains block the replication and the dissemination of viruses in the mosquito. Some studies suggest that pathogen blocking is due to Wolbachia priming the insect innate immune system. Here, we show that Wolbachia induces transcription of some immunity related genes only in its new host A. aegypti, and not in its natural host D. melanogaster, while Wolbachia reduces dengue replication in both hosts. These results suggest that immune priming by Wolbachia might not be the only mechanism responsible for viral interference.

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.

Dengue type 3 infection--Nicaragua and Panama, October-November 1994

The geographic range and incidence of dengue virus activity in the Americas substantially increased from 1980 to 1994. During this period, all dengue activity in the Americas was associated with dengue serotypes 1, 2, and 4 (DEN-1, DEN-2, and DEN-4). On November 25, 1994, the Ministry of Health of Nicaragua announced the isolation of dengue type 3 (DEN-3) from two children hospitalized with minor hemorrhagic manifestations in Managua. Subsequently, DEN-3 virus was isolated from two persons with dengue fever in Panama. These cases represent the first isolation of DEN-3 from autochthonous cases in the Americas since 1977. This report describes these cases and dengue activity in Nicaragua and Panama and summarizes public health activities to control dengue fever in the Americas.

Analysis of C-terminally truncated dengue 2 and dengue 3 virus envelope glycoproteins: processing in insect cells and immunogenic properties in mice

We constructed two recombinant Autographa californica nuclear polyhedrosis baculoviruses. Spodoptera frugiperda (Sf9) cells containing these constructs produce carboxy-terminally truncated envelope E proteins representing dengue (DEN) virus serotypes 2 and 3. The two recombinant proteins contained their homologous signal sequences at the N terminus and were truncated by 71 and 74 amino acids at the C terminus, respectively. This allowed the translocation of the recombinant proteins to the endoplasmic reticulum followed by glycosylation processing and secretion into the extracellular medium. An additional unglycosylated form which was not secreted was detected inside the infected Sf9 cells. Sera from Swiss mice immunized with the infected Sf9 cell lysates gave a DEN cross-reactive response in ELISA and substantial amounts of neutralizing antibodies to the homologous virus. Similar antibody titres were obtained when the two recombinant proteins were inoculated concomitantly. BALB/c mice were vaccinated with three doses of the recombinant E proteins, taken as monovalent or bivalent immunogens, and challenged with mouse-adapted DEN-2 virus. DEN-2 E protein induced a good protection (90%) against lethal encephalitis and recombinant DEN-3 E protein gave a substantial cross-protection (54%). Eighty-two percent of the mice immunized with a mixture of both recombinant E proteins survived the DEN-2 virus challenge.

Dengue 2 virus enhancement in asthmatic and non asthmatic individual

During the 1981 dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) Cuban epidemic, bronchial asthma (BA) was frequently found as a personal or family antecedent in dengue hemorrhagic fever patients. Considering that antibody dependent enhancement (ADE) plays an important role in the etiopathogenic mechanism of DHF/DSS, we decide to study the Dengue 2 virus (D2V) capability of replication in peripheral blood leukocytes (PBL) from asthmatic patients and healthy persons. In 90% of asthmatic patients and 53.8% of control group it was obtained PBL with a significant D2V enhancing activity (X2 p < 0.01). Power enhancement was higher in asthmatic group. This is the first in vitro study relating BA and the dengue 2 virus immuno enhancement. The results obtained support the role of BA as a risk factor for DHF/DSS as already described on epidemiological data.

A rapid method for detection and identification of flaviviruses by polymerase chain reaction and nucleic acid hybridization

A polymerase chain reaction (PCR) technique was developed and evaluated for the detection of flaviviruses. A set of sense and antisense oligomeric DNA primers were constructed from nucleotide sequences of the conserved region of the genome of several different flaviviruses. Virus specific complementary DNA (cDNA) was prepared by reverse transcription of total RNA extracted from infected cell cultures. Amplified cDNA was identified by nucleic acid hybridization with specific oligomeric internal probes. Various conditions, such as number of cycles and annealing temperature were examined to optimize the detection of viral RNAs from infected cell cultures. Slot blot hybridization with a radioactive probe was used to evaluate the sensitivity of PCR amplification. The PCR amplified RNA sequences of dengue 2 (DEN-2), West Nile (WN), St. Louis encephalitis (SLE) and Kunjin (KUN) virus and detected 0.1 to 1 pg of viral RNA. Japanese encephalitis (JE), Yellow Fever virus (YF), DEN-1, 3, and 4 viruses were not amplified. The more frequent occurrence of mismatches in the 3' primer binding site may explain the failure to amplify cDNA of these viruses.

Imported dengue--United States, 1992

Dengue is a mosquito-transmitted acute disease caused by any of four virus serotypes (DEN-1, DEN-2, DEN-3, and DEN-4) and characterized by the sudden onset of fever, headache, myalgia, rash, nausea, and vomiting. The disease is endemic in most tropical areas of the world and can occur in U.S. residents returning from international travel. Serum samples from 68 persons with suspected imported dengue with onset in 1992 (1) were submitted to CDC from 23 states (Table 1). Of these, 17 (25%) cases (from 10 states) were serologically or virologically diagnosed as dengue. This report summarizes information about these 17 cases.

An integrated target sequence and signal amplification assay, reverse transcriptase-PCR-enzyme-linked immunosorbent assay, to detect and characterize flaviviruses

We previously described a reverse transcriptase-PCR using flavivirus genus-conserved and virus species-specific amplimers (D. W. Trent and G. J. Chang, p. 355-371, in Y. Becker and C. Darai; ed., Frontiers of Virology, vol. 1, 1992). Target amplification was improved by redesigning the amplimers, and a sensitive enzyme-linked immunosorbent assay (ELISA) technique has been developed to detect amplified digoxigenin (DIG)-modified DNA. A single biotin motif and multiple DIG motifs were incorporated into each amplicon, which permitted amplicon capture by a biotin-streptavidin interaction and detection with DIG-specific antiserum in a colorimetric ELISA. We evaluated the utility of this assay for detecting St. Louis encephalitis (SLE) viral RNA in infected mosquitoes and dengue viral RNA in human serum specimens. The reverse transcriptase-PCR-ELISA was as sensitive as isolation of SLE virus by cell culture in detecting SLE viral RNA in infected mosquitoes. The test was 89% specific and 95 to 100% sensitive for identification of dengue viral RNA in serum specimens compared with isolation of virus by Aedes albopictus C6/36 cell culture and identification by the indirect immunofluorescence assay.

[Application of reverse transcription-polymerase chain reaction in rapid diagnosis and serotype identification of dengue virus infections]

RT-PCR was developed for the amplification of partial E genome fragment from four dengue serotypes. Of the six oligonucleotide primers designed one was shared by dengue virus type 1 and type 2, and one by type 3 and type 4. Each of the other four primers was type specific. Amplified products with 240, 150, 333 and 421 bp, respectively were identified by electrophoresis on 2% agarose gel and digestion with restriction enzyme Hind III. RT-PCR can detect dengue viral RNA from at least 5TCID50 virus, which was confirmed by detection of serial dilutions of culture supernatants. RT-PCR was also applied to serum samples from 60 acute patients. The findings showed that RT-PCR was of the same specificity as isolation of virus, followed by indirect fluorescent antibody tests. RT-PCR was more sensitive than cell culture and can be used for the rapid diagnosis and serotype identification of dengue virus infections.

Differences between cell membrane fusion activities of two dengue type-1 isolates reflect modifications of viral structure

The genetic diversity of dengue (DEN) virus was explored using two South American DEN-1 virus strains isolated from viremic human sera. DEN-1 virus strains BR/90 and FGA/89 were selected on the basis of their membrane fusion properties in mosquito cell cultures. Infection of mosquito cell lines with BR/90 virus strain induced a cytopathic effect characterized by syncytium formation whereas no cytopathic changes were observed with FGA/89. Cell-to-cell fusion experiments indicated that the fusogenic activity of FGA/89 required a lower pH than BR/90. Immunoreactivity analysis of the DEN-1 envelope (E) protein with monoclonal antibodies revealed a minor difference between the antigenic structures of FGA/89 and BR/90 virions. FGA/89 was less neurovirulent than BR/90 for newborn mouse. To determine the genetic origin of these modifications, the amino acid sequences of the structural proteins from these virus strains were compared. One amino acid difference was found within the carboxy-terminal domain of protein C. Five amino acid substitutions were found in the E proteins at positions 96, 180, 297, 379, and 473. Changes at positions 96, 297, and 379 map within two overlapping antigenic domains of protein E. These limited amino acid differences in the E protein could affect the biological properties and the antigenicity of the DEN virion.

Dengue epidemic in the stage of Rio de Janeiro, Brazil, 1990-1: co-circulation of dengue 1 and dengue 2 serotypes

During 1990 and 1991, dengue fever was detected in the State of Rio de Janeiro, Brazil. It occurred in two epidemic waves; one, from January to August 1990, caused predominantly by dengue virus type 1 (DEN-1) the other from October 1990 to May 1991 caused by type 2 virus (DEN-2). Dengue was confirmed by virus isolation and/or IgM capture enzyme-linked immunosorbent assay (MAC-ELISA) in 2109/5964 (35.4%) of the cases. DEN-2 virus was isolated from 180 patients. HAI tests indicated that of these previous infection with DEN-1 had occurred in 130 (72%). The epidemic was classified as dengue fever, but severe and even fatal cases occurred in association with secondary infection.

Ultra-rapid, simple, sensitive, and economical silica method for extraction of dengue viral RNA from clinical specimens and mosquitoes by reverse transcriptase-polymerase chain reaction

A rapid, simple and efficient single-tube procedure is described for the isolation of dengue virus RNA from small amount of serum (10 microliters) followed by a reverse transcriptase-polymerase chain reaction (RT-PCR). Recovery of RNA is based on the lysing and nuclease-inactivating properties of guanidinium thiocyanate in the presence of silica. The silica RT-PCR can be completed within 5 hours starting from RNA extraction to agarose gel electrophoresis. All of the 63 dengue-3 culture-positive sera were RT-PCR-positive (virus titres: < 10(2) to 11(10.69.). Of 33 culture-negative acute sera from serologically confirmed dengue fever patients collected during dengue-3 epidemic, 4 were RT-PCR-positive. RT-PCR was also positive in 29 of 30 dengue-1 culture-positive sera (virus titres range: < 10(2) to 10(8.69). Dengue-1 virus was also detected in field-caught Aedes aegypti mosquitoes by silica RT-PCR.

[A study on a local epidemic of dengue fever in Shaxi district of Zhongshan city, 1991]

An epidemic of dengue fever occurred in Shengshi Village of Shaxi District in the last ten-day period of August, 1991. A wrong diagnosis was made on account of atypical clinical symptoms and careless investigation during early days. Effective measures had not been taken in time, so that the disease spread to neighbouring three villages and the town. The epidemic lasted for 64 days and 112 cases were found. It had been proven by etiologic studies that type 1 dengue virus caused this epidemic.

Genetic and biological differentiation of dengue 3 isolates obtained from clinical cases in Java, Indonesia, 1976-1978

Previous epidemiological, virological and clinical studies have documented a series of outbreaks of dengue fever and dengue haemorrhagic fever/dengue shock syndrome which occurred in Java, Indonesia in 1976-1978. In the current study we compare growth characteristics in cell culture, and nucleotide sequence data for the viral prM and E genes, of five low passage DEN-3 isolates obtained during these epidemics from clinically defined cases. All isolates had the same passage history: human sera were passed twice in mosquitoes and three times in a mosquito cell line (Aedes albopictus, C 6/36 cells). Growth differences were observed between individual isolates in Vero cells; growth differences were not observed in C 6/36 cells. Nucleotide sequencing of the prM and E gene region indicated that no two isolates were identical (sequence divergence ranged from 0.4 to 1.6% in pairwise comparisons) but that they were closely enough related to present a single genetic type. There were one or two differences in deduced amino acid sequence in E between isolates. Differences were at residues 65, 187, 298 or 443. One isolate differed from all others at residue 16 in the M protein. No relationship was apparent between the amino acid sequence of M or E and the nature of the disease profile, the year of isolation or the geographic region of isolation. The isolates showed 3.5 to 4.4% nucleotide sequence divergence from the highly-adapted H 87 prototype, isolated in the Philippines in 1956. The isolates showed a total of twelve common amino acid differences in prM and E proteins from H 87. Ten of these twelve residues were at positions which differed between the four dengue serotypes. Two differences (at residues 37 in M and 293 in E) were at positions which are conserved in sequence between the four dengue serotypes. The data are discussed in relation to the dengue outbreaks in Java in the period 1976-1978.

Dengue epidemic in the state of Rio de Janeiro, Brazil: virological and epidemiological aspects

Laboratory studies were carried out on 3178 patients with signs and symptoms suggestive of dengue infection from April 1986 to December 1987 in the State of Rio de Janeiro, Brazil. The epidemic had two peaks following the first virus isolation and affected the inhabitants of 17 counties. Both sex and all age groups were affected. Dengue virus type 1 was isolated from 1039 sera and the number of confirmed cases was increased to 1874 (59%) by MAC-ELISA. Isolation rate confirmed cases reached 80% in the specimens obtained until the 4th day after the onset of disease and viraemia ranged from 10(3.0) to 10(8.5) TCID50/ml.

Direct sequencing of genomic cDNA fragments amplified by the polymerase chain reaction for molecular epidemiology of dengue-2 viruses

A nucleotide fragment encoding amino acids 29 to 94 in the E-protein of 28 dengue-2 isolates of diverse geographic and host origins was examined by direct sequencing of a polymerase chain reaction (PCR)-amplified product, and compared to six previously published sequences. Nucleotide divergence ranged from 0 to 19.8% corresponding to a maximum of 9% divergence in the amino acid sequence. Taking a divergence of 6% between the nucleotide sequence as a cut off for genotype classification, six groups have been established. Southeast Asian and the Jamaican 1983 genotypes show a high rate of similarity (> 95.2%). Our results suggest that virus of this group is now circulating as the dominant topotype in Brazil (1990) and in French Guyana (1986-1991). African strains fall into two groups, one endemic group (1970-1990) and one epidemic group (1986-1987). The three other groups correspond to viruses from Sri Lanka (1982) and the Seychelles (1977), from Puerto Rico (1973) and from Tahiti (1975). Our approach appears to be valuable characterizing dengue isolates, easily and rapidly.

Dengue haemorrhagic fever (DHF) outbreak in Calcutta--1990

An outbreak of Dengue Haemorrhagic Fever (DHF) occurred in Calcutta between September and December, 1990. Children and young adults were the major victims. Haemorrhagic manifestations and shocks were the main features in most of the hospitalised cases. Five mouse pathogenic agents were isolated from 105 acute cases and all were identified as DEN-3. HI and CF test with 55 paired sera revealed evidence of dengue infection in 33 (60 per cent) and flavivirus group reaction including dengue in 17 (30.9 per cent). It was for the first time, that DEN-3 was considered to be the etiologic agent for DHF in Calcutta.

Detection of dengue virus by in situ hybridization

A non-radioactive in situ hybridization protocol was developed for the detection of dengue virus RNA in fixed tissues and cells. For this purpose a riboprobe was constructed from a 39 base sequence, from the capsid protein coding region of the genome, which is conserved in the four dengue serotypes. The ability of this probe to specifically detect dengue RNA from each serotype was confirmed on brain sections from infected mice. Dengue viral RNA was also detected in in vitro infected human primary endothelial cells which release infectious virus without showing gross cytopathic effect. With clinical samples dengue viral RNA was detected in some preparations of white blood cells from dengue fever patients and in thymus autopsy sections following suspected death from dengue shock syndrome. For dengue samples of undetermined serotype the sensitivity of the short probe was compared to that of an equimolar mixture of long (260 base) probes from the envelope coding region of the four dengue serotypes, provided by Dr. V. Deubel. In those samples examined, sensitivity of the long probe mixture was greater and higher numbers of infected cells were detected.

Dengue in China: a clinical review

Three etiologically proven outbreaks of dengue fever and one etiologically confirmed epidemic of dengue haemorrhagic fever have occurred in south China since 1978. The first of these, an epidemic of dengue due to virus type 4 took place in Shiwan town, Foshan city, Guangdong Province, in 1978; the epidemic began in May and ended in November. The clinical manifestations of 583 hospitalized patients were observed from August to October. The majority (81.3%) of patients were aged 21-50 years (male:female = 1.2:1). The course of illness was about 1 week in most cases; three patients (0.5%) died. A local outbreak of dengue due to virus type 1 occurred in Shiqi town, Zhongshan County, Guangdong Province, from September to November 1979. The majority of patients were older children and adolescents. There was no marked difference between males and females in terms of the course of the illness, and there were no complications or deaths. A large epidemic of dengue due to virus type 3 occurred on Hainan Island in 1980. The clinical manifestations of 510 hospitalized patients (mostly adolescents and adults) were observed from April to September. Some patients developed rare complications, such as loss of hair, acute intravascular haemolysis, and multiple peripheral paralysis; there were four deaths (0.78%). The first known epidemic of dengue haemorrhagic fever in China occurred among 10-29-year-olds on Hainan Island in 1985 and 1986. There were no essential differences between males and females. Some cases had rare complications such as acute intravascular haemolysis, while others had diffuse intravascular coagulation and altered mental status; 10 patients (6.5%) died.

Applications of polymerase chain reaction for identification of dengue viruses isolated from patient sera

A simple and sensitive procedure of reverse transcriptase polymerase chain reaction (RT-PCR) was developed previously such that all 4 serotypes of dengue viruses could be detected and their serotypes identified simultaneously in a single-step procedure. In this study we compared the RT-PCR with a conventional immunoperoxidase (PAP) staining method for the identification of dengue viruses currently isolated from patient sera. Sixty-six sera taken from dengue hemorrhagic fever (DHF) patients were subjected to virus isolation by inoculating onto C6/36 cell cultures. Screening for the presence of dengue viruses in culture fluids was done after 7 days of incubation by PAP staining using hyperimmune rabbit anti-dengue virus antibody as the primary reagent. Dengue viruses in positive cultures were further identified for their serotypes by PAP using type-specific monoclonal antibodies (MAb) and by RT-PCR. Thirty-two out of the 66 serum specimens tested (48.5%) were positive for dengue viruses. Of these, 5 were type 1 (DEN-1), 25 were type 2 (DEN-2) and 2 contained both DEN-1 and DEN-2. All cultures that were positive by PAP method were also positive by RT-PCR and vice versa. Thus, the results obtained by RT-PCR were in good agreement with those by PAP. It is important to point out that while all 5 DEN-1 isolates reacted readily with the MAb 1F1, only 2 of them could be identified by the MAb 15F3. Our data suggest that antigenic variation among DEN-1 isolates occur frequently and this should be taken into consideration in the selection of appropriate type-specific MAb for serotyping of dengue viruses.(ABSTRACT TRUNCATED AT 250 WORDS)

Replication of dengue viruses in mosquito cell cultures: a model from ultrastructural observations

Mosquito cell cultures infected with human sera from dengue-1 and dengue-2 outbreaks, started in Rio de Janerio by 1986 and 1990 respectively, were examined by electron microscopy at different times post the infection of cell cultures. More information was obtained about cell penetration of virus particles in the presence or not of antibodies, their pathway inside the cells, replication mode and exist. Infectiveness of the virus at those different stages can only be attributed to the particles appearing inside the trans-Golgi vesicles; most of all newly formed virus particles remain inside the RER-derived cell vesicles or inside lysosomes, even during cell lysis. Groups of larger particles, 65-75 nm in diameter at dengue-2 infections, persist during cell passage. The large amounts of smooth membrane structures, as vesicles or tubules inside the RER, are attributed to a cell response to viral infection.

Use of dengue blot in dengue diagnosis: the Malaysian experience

Dengue fever/Dengue haemorrhagic fever (DF/DHF) has been a public health problem in Malaysia with an endemic level of about 7 per 100,000 population per year. In 1990, Malaysia experienced its most severe outbreak of DF/DHF with a record total of 5,590 cases referred to the Division of Virology, Institute for Medical Research (IMR). Of these, 1,880 were confirmed serologically to be DF/DHF. The conventional serological procedure, the Haemagglutination Inhibition (HI) test, for the diagnosis of DF/DHF is cumbersome and causes delay in diagnosis. Another problem associated with the HI test has been that it has often been difficult to obtain a second convalescent serum sample for an accurate diagnosis. This has raised an urgent need to establish a "rapid" test for diagnosis of DF/DHF. As such the authors recently carried out an evaluation of a newly available commercial rapid test, namely, the Dengue Blot Assay (Diagnostic Biotechnology Singapore Pte Ltd). The test is intended for use in laboratory confirmation of dengue virus infection. The evaluation was to determine if the test could be utilised as a routine laboratory test and to establish its sensitivity and specificity. Over 400 samples were tested against the Dengue Blot Assay. Results were checked against an in-house Dengue IgM ELISA and HI assay. Preliminary results indicate that the sensitivity and specificity of the Dengue Blot is satisfactory. Our results also indicate that the Dengue Blot has a useful role to play in a routine laboratory especially since it provides rapid results on single serum samples thereby reducing the workload in a busy diagnostic laboratory.

Dengue activity in Puerto Rico, 1990

Reported dengue activity in Puerto Rico (PR) increased in 1990 for the fourth consecutive year. The Community Hygiene Division of the PR Health Department received 9,540 reports of suspected dengue cases. Of the blood samples obtained from 7,660 patients, 1,911 were confirmed as dengue infection by laboratory tests at the Dengue Branch, San Juan Laboratories, Centers for Disease Control. Dengue 2 (DEN-2) continued to be the most frequently isolated serotype among all confirmed cases, hospitalized patients, and the confirmed cases with hemorrhagic manifestations. Disease was reported throughout the island and during all months, but activity, as in previous years, was lowest from April through July, and highest from September to November. The highest rates of laboratory-confirmed illness occurred in towns on the south coast and in the central mountains, with only one or two circulating virus serotypes (DEN-2 in the south; DEN-2 and DEN-4 in the central mountains). Although cases were confirmed in infants and octogenarians, the majority of laboratory-confirmed cases (1,293, 68%), and the highest attack rates (0.70/1000), were reported in persons younger than 30. Of patients with confirmed cases, 289 (15%) were hospitalized, and 438 (23%) reported at least one hemorrhagic manifestation. One presumptive dengue case with fatal outcome was reported in 1990 in a 17-year-old woman in whom a febrile illness, seizures, and coma developed; she died after cardiorespiratory arrest. Recent dengue infection in this individual was serologically documented, but no virus was isolated.

Rapid detection and typing of dengue viruses from clinical samples by using reverse transcriptase-polymerase chain reaction

We report on the development and application of a rapid assay for detecting and typing dengue viruses. Oligonucleotide consensus primers were designed to anneal to any of the four dengue virus types and amplify a 511-bp product in a reverse transcriptase-polymerase chain reaction (PCR). First, we produced a cDNA copy of a portion of the viral genome in a reverse transcriptase reaction in the presence of primer D2 and then carried out a standard PCR (35 cycles of heat denaturation, annealing, and primer extension) with the addition of primer D1. The resulting double-stranded DNA product of the RT-PCR was typed by two methods: dot blot hybridization of the 511-bp amplified product to dengue virus type-specific probes or a second round of PCR amplification (nested PCR) with type-specific primers, yielding DNA products the unique sizes of which were diagnostic for each dengue virus serotype. The accumulated data demonstrated that dengue viruses can be accurately detected and typed from viremic human serum samples.

Dengue 1 epidemic in French Polynesia, 1988-1989: surveillance and clinical, epidemiological, virological and serological findings in 1752 documented clinical cases

An epidemic of dengue 1 occurred in French Polynesia in December 1988 and June 1989. This paper records (i) the trend of the outbreak and its surveillance and (ii) the clinical, epidemiological and virological data obtained from 1752 documented cases. The epidemic reached its peak in February in Tahiti Island, 7 weeks after its recognition. Among 6034 suspect cases reported by sentinel physicians, 60.3% were < 20 years old. The illness was classical dengue. No fatality or case of dengue haemorrhagic fever/dengue with shock syndrome was reported. Of 4792 patients subjected to laboratory testing, 41% were confirmed as positive. The serological attack rate was c. 40%. The estimated number of dengue infections in the Windward Islands was about 20,000. Transmission was associated with Aedes aegypti. Study of documented cases showed a higher confirmation rate in both the civilian population < 15 years old (46.5%) and the susceptible French military population (47.6%) than in older civilians (31.1%, P < 0.05). Furthermore, primary dengue infections were predominant in both of the first 2 groups. The diagnosis was mostly confirmed (i) by virus isolation on day < 5 of illness and (ii) by detection of immunoglobulin (Ig) M on day > or = 5 of illness. The study showed that adequate surveillance of an epidemic requires both clinically and laboratory-based systems.

Recent advances and prospective researches on molecular epidemiology of dengue viruses

The determination of amino acid changes in the envelope protein by direct sequencing of either genomic RNA or PCR-amplified cDNA fragments provides useful informations for assessing the genetic variability and the geographic distribution of the actually most widespread dengue-2 serotype. The possible link of variations in the envelope protein-gene and virus virulence is discussed.

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

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

NS 1 gene sequences from eight dengue-2 viruses and their evolutionary relationships with other dengue-2 viruses

The nucleotide sequences of the NS 1 genes from five Thai and three Sri Lankan dengue-2 viruses were determined by sequencing the viral RNA using synthetic oligonucleotide primers. The results were shown to be similar to four published dengue-2 NS 1 sequences and the classification of these genes was compared with the one obtained for the envelope genes of the same viruses. The classification was similar and showed that the Thai isolates could be divided into two separate groups and that the Sri Lankan isolates were distinct. We found no correlation between disease severity, serological response (1 degree or 2 degrees), or year of isolation and various aspects of NS 1 protein sequence variation; and no particular amino acid changes were correlated with virulence. The sequences were combined with those published and classified elsewhere to provide a comprehensive E/NS 1 gene taxonomy of dengue-2 virus isolates.