A simple one-step real-time RT-PCR for diagnosis of dengue virus infection

Epidemiological screening and serotyping analysis of dengue fever in the Southwestern region of Saudi Arabia

Dengue is an acute systemic viral disease that has been developed globally in both chronic and epidemic transmission periods. Dengue virus (DENV) is a member of the Flavivirus genus of the Flaviviridae family, which endangers public health. Limited studies have been performed in the Saudi Arabia and there are no epidemiological as well as molecular screening of DENV in the Southwestern region and this current study was conducted on the epidemiology of dengue in the Southwestern region of Saudi Arabia. Simultaneously, we have screened the 100 patients for DENV using the real-time reverse transcriptase polymerase chain reaction (RT-PCR) assay. The current study results confirmed that 6637 people from various hospitals and locations in Jazan, Southwestern regions, were enrolled in this study from 2012 to 2020. The overall mean age was 30.02 ± 18.01 years, with 62.8% of males and 37.2% of females enrolled. This study included nearly three-fourths of the Saudi participants and one-fourth of the expatriates, and 56.6% of the positive cases were enrolled. In 2019, the most instances were enrolled, with 44% of positive cases. When screened using the RT-PCR assay, 93% of the positive patients were recruited, according to the quality control analysis. In conclusion, the current study results confirmed the prevalence of DENV was increased drastically since 2012 to 2020. High number of cases were registered prior to the Pandemic. The screening for DENV was performed with RT-PCR assay and NSI antigen should also be implemented to cross-check the results which was previously performed with RT-PCR analysis.

Revisiting the dengue epidemic of 2011 in Paraguay: molecular epidemiology of dengue virus in the Asuncion metropolitan area

Background

Dengue is one of the most important re-emerging viral diseases and the most common human arthropod-borne viral infection worldwide. Any of the four Dengue virus serotypes (DENV-1 to 4) can cause asymptomatic infections or clinical manifestations that range in severity from a mild, self-limited illness, to a severe disease characterized by a shock syndrome that can lead to death. Paraguay suffers periodic epidemic outbreaks of dengue since 1988 when the DENV-1 was introduced in the country. Epidemics caused by all four serotypes have been reported and the country. Although dengue is endemic in Paraguay, few studies have described the molecular epidemiology of DENV in the country, which is important to understand the local and global spread, as well as the evolution of this pathogen.

Methods

This was a cross-sectional study of a convenience sample. Suspected dengue patients of any age were recruited from the Emergency Laboratory of the Central Hospital of the Institute of Social Welfare, Asuncion, Paraguay, from February to June of 2011. A DENV antigen test was used to confirm the infection. The protein E gene sequences of isolated viruses were sequenced for phylogenetic analysis.

Results

Dengue was confirmed in 55.1% of the participants (n = 98/178). The most frequent clinical findings were fever, headache, and myalgia. Identity analyses of the protein E gene sequence of 56 viruses isolated showed the circulation of DENV-1 (n = 45) and DENV-2 (n = 11) in the Asuncion metropolitan area in 2011. Molecular epidemiology analyses suggest that DENV-1 was introduced into Paraguay from Argentina, while the DENV-2 from Brazil, replacing previous virus lineages.

Conclusions

We have analyzed the molecular epidemiology of DENV-1 and DENV-2 isolated in Paraguay in 2011. We found strong evidence that DENV-1 was introduced into Paraguay from Argentina, while the DENV-2 from Brazil, replacing previous virus lineages. Molecular epidemiology studies are of great interest to analyze the dynamic of DENV spread, which are useful for early implementation of containment measures to reduce the risk of explosive epidemics caused by this virus.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06487-9.

Wastewater-Based Epidemiology for Early Detection of Viral Outbreaks

The immense global burden of infectious disease outbreaks and the need to establish prediction and prevention systems have been recognized by the World Health Organization (WHO), the National Institutes of Health (NIH), the United States Agency of International Development (USAID), the Bill and Melinda Gates Foundation, and the international scientific community. Despite multiple efforts, this infectious burden is still increasing. For example, it has been reported that between 1.5 and 12 million people die each year from waterborne diseases and diarrheal diseases are listed within the top 15 leading causes of death worldwide. Rapid population growth, climate change, natural disasters, immigration, globalization, and the corresponding sanitation and waste management challenges are expected to intensify the problem in the years to come.

DNA Microarray Platform for Detection and Surveillance of Viruses Transmitted by Small Mammals and Arthropods

Viruses transmitted by small mammals and arthropods serve as global threats to humans. Most emergent and re-emergent viral agents are transmitted by these groups; therefore, the development of high-throughput screening methods for the detection and surveillance of such viruses is of great interest. In this study, we describe a DNA microarray platform that can be used for screening all viruses transmitted by small mammals and arthropods (SMAvirusChip) with nucleotide sequences that have been deposited in the GenBank. SMAvirusChip was designed with more than 15,000 oligonucleotide probes (60-mers), including viral and control probes. Two SMAvirusChip versions were designed: SMAvirusChip v1 contains 4209 viral probes for the detection of 409 viruses, while SMAvirusChip v2 contains 4943 probes for the detection of 416 viruses. SMAvirusChip was evaluated with 20 laboratory reference-strain viruses. These viruses could be specifically detected when alone in a sample or when artificially mixed within a single sample. The sensitivity of SMAvirusChip was evaluated using 10-fold serial dilutions of dengue virus (DENV). The results showed a detection limit as low as 2.6E3 RNA copies/mL. Additionally, the sensitivity was one log10 lower (2.6E2 RNA copies/mL) than quantitative real-time RT-PCR and sufficient to detect viral genomes in clinical samples. The detection of DENV in serum samples of DENV-infected patients (n = 6) and in a whole blood sample spiked with DENV confirmed the applicability of SMAvirusChip for the detection of viruses in clinical samples. In addition, in a pool of mosquito samples spiked with DENV, the virus was also detectable. SMAvirusChip was able to specifically detect viruses in cell cultures, serum samples, total blood samples and a pool of mosquitoes, confirming that cellular RNA/DNA did not interfere with the assay. Therefore, SMAvirusChip may represent an innovative surveillance method for the rapid identification of viruses transmitted by small mammals and arthropods.

Development and Evaluation of a SYBR Green-Based Real-Time Multiplex RT-PCR Assay for Simultaneous Detection and Serotyping of Dengue and Chikungunya Viruses

Chikungunya virus (CHIKV) and dengue virus (DENV) have emerged as the two most important arbovirus diseases of global health significance. Similar clinical manifestations, transmission vectors, geographical distribution, and seasonal correlation often result in misdiagnosis of chikungunya infections as dengue cases and vice versa. In this study, we developed a rapid and accurate laboratory confirmative method to simultaneously detect, quantify, and differentiate DENV serotypes 1, 2, 3, and 4 and CHIKV. This SYBR Green I–based one-step multiplex real-time RT-PCR assay is highly sensitive and specific for CHIKV and DENV. Melting temperature analysis of PCR amplicons was used to serotype DENV and to differentiate from CHIKV. The detection limit of the assay was 20, 10, 50, 5, and 10 RNA copies/reaction for DENV-1, DENV-2, DENV-3, DENV-4, and CHIKV, respectively. Our assay did not cross-react with a panel of viruses that included other flaviviruses, alphaviruses, influenza viruses, human enteroviruses, and human coronaviruses. The feasibility of using this assay for clinical diagnosis was evaluated in DENV- and CHIKV-positive patient sera. Accordingly, the assay sensitivity for DENV-1, DENV-2, DENV-3, DENV-4, and CHIKV was 89.66%, 96.67%, 96.67%, 94.12%, and 95.74%, respectively, with 100% specificity. These findings confirmed the potential of our assay to be used as a rapid test for simultaneous detection and serotyping of DENV and CHIKV in clinical samples.

Development and Validation of a Quantitative, One-Step, Multiplex, Real-Time Reverse Transcriptase PCR Assay for Detection of Dengue and Chikungunya Viruses

Dengue virus (DENV) and chikungunya virus (CHIKV) are important human pathogens with common transmission vectors and similar clinical presentations. Patient care may be impacted by the misdiagnosis of DENV and CHIKV in areas where both viruses cocirculate. In this study, we have developed and validated a one-step multiplex reverse transcriptase PCR (RT-PCR) to simultaneously detect, quantify, and differentiate between four DENV serotypes (pan-DENV) and chikungunya virus. The assay uses TaqMan technology, employing two forward primers, three reverse primers, and four fluorophore-labeled probes in a single-reaction format. Coextracted and coamplified RNA was used as an internal control (IC), and in vitro-transcribed DENV and CHIKV RNAs were used to generate standard curves for absolute quantification. The diagnostic 95% limits of detection (LOD) within the linear range were 50 and 60 RNA copies/reaction for DENV (serotypes 1 to 4) and CHIKV, respectively. Our assay was able to detect 53 different strains of DENV, representing four serotypes, and six strains of CHIKV. No cross-reactivity was observed with related flaviviruses and alphaviruses, To evaluate diagnostic sensitivity and specificity, 89 clinical samples positive or negative for DENV (serotypes 1 to 4) and CHIKV by the standard virus isolation method were tested in our assay. The multiplex RT-PCR assay showed 95% sensitivity and 100% specificity for DENV and 100% sensitivity and specificity for CHIKV. With an assay turnaround time of less than 2 h, including extraction of RNA, the multiplex quantitative RT-PCR assay provides rapid diagnosis for the differential detection of two clinically indistinguishable diseases, whose geographical occurrence is increasingly overlapping.

High prevalence of clinically unsuspected dengue disease among children in Ribeirao Preto city, Brazil

The aim of this study was to analyze the characteristics of Dengue virus (DENV)-infected children and the accuracy of dengue diagnosis based on clinical presentations. The inclusion criteria were children ≥1-year-old presenting febrile illness with 1-7 days of onset. Children (n = 110) aged 2-15 years were included in this study. DENV infection was confirmed with virological tests using serum, salvia, and/or urine samples. The attending pediatricians classified 56/110 (50.91%) of the children as suspected dengue cases. The DENV infection was confirmed by specific laboratory tests in 52/56 (92.9%) of the suspected dengue cases but also in 44/54 (81.5%) of the unsuspected dengue cases; total of 96/110 (87.27%) confirmed dengue cases. The clinical diagnosis gave an overall sensitivity of 54.2% (52/96) and a specificity of 71.4% (10/14). The positive predictive value of the clinical diagnosis was 92.8% and negative predictive value was 18.5%. After the third day of onset of symptoms, the DENV genome detection rate was similar in serum and saliva samples, suggesting that saliva samples represent an alternative to blood samples for early dengue diagnosis. Vaccination against Yellow fever virus did not influence the antibody response against DENV-1, DENV-2, and DENV-3, which circulated during the study period. Although the signs and symptoms were compatible with dengue, the attending pediatricians did not suspect the disease in several children. Therefore, the inclusion of virological tests for early diagnosis in the protocols for dengue surveillance would help in the implementation of prompt treatment of patients and epidemic containment strategies. J. Med. Virol. 88:1711-1719, 2016. © 2016 Wiley Periodicals, Inc.

Tackling dengue fever: Current status and challenges

According to recent statistics, 96 million apparent dengue infections were estimated worldwide in 2010. This figure is by far greater than the WHO prediction which indicates the rapid spread of this disease posing a growing threat to the economy and a major challenge to clinicians and health care services across the globe particularly in the affected areas.This article aims at bringing to light the current epidemiological and clinical status of the dengue fever. The relationship between genetic mutations, single nucleotide polymorphism (SNP) and the pathophysiology of disease progression will be put into perspective. It will also highlight the recent advances in dengue vaccine development.Thus far, a significant progress has been made in unraveling the risk factors and understanding the molecular pathogenesis associated with the disease. However, further insights in molecular features of the disease and the development of animal models will enormously help improving the therapeutic interventions and potentially contribute to finding new preventive measures for population at risk.

Differential replicative ability of clinical dengue virus isolates in an immunocompetent C57BL/6 mouse model

BACKGROUND

Several experimental animal models have been used to study the pathogenesis of dengue disease; however, most of the studies used laboratory-adapted viruses, which lack the virulence of viruses circulating in humans. The aim of this study was to analyze the ability of clinical Dengue virus (DENV) isolates (D2/BR/RP/RMB/09 and D3/BR/SL3/02) to infect immunocompetent C57BL/6 mice.

METHODS

Two strategies of intraperitoneal infection, which were based on the concept of the antibody dependent enhancement phenomenon, were used. In one strategy, the animals were inoculated with macrophages infected in vitro with dengue viruses, which were incubated with enhancing antibodies, and in the other strategy, the animals were inoculated with a complex of enhancing antibodies and dengue viruses.

RESULTS

The D3/BR/SL3/08 isolate showed a higher ability of infection (virus RNA was more frequently detected in the serum and in several organs) in the experimental model compared to both the D2/BR/RP/RMB/2009 isolate and a laboratory adapted DENV-1 strain (Mochizuki strain), regardless of the infection strategy used. The main features of the D3/BR/SL3/08 isolate were its neuroinvasiveness and the induction of an extended period of viremia. Enhancing antibodies did not influence on the infection of animals when macrophages were used, but the level of viremia was increased when they were used as a complex with a D3/BR/SL3/02 isolate.

DISCUSSION

We showed that DENV isolates could infect immunocompetent C57BL/6 mice, which have has been previously used to study some aspect of dengue disease when infected with laboratory adapted strains. DENV genome was detected in the same organs found in humans when autopsy and biopsy samples were analyzed, showing that C57BL/6 mice reproduce some aspects of the DENV tropism observed in humans. The main difference observed between the D3/BR/SL3/02 and D2/BR/RP/RMB/2009 clinical isolates was the neuroinvasive ability of the first one. Neuroinvasiveness has been described in some DENV infected cases and is common for other members of the Flavivirus genus.

CONCLUSIONS

These results suggest that C57BL/6 mice can be used as an experimental model to evaluate virulence differences among DENV clinical isolates.

Galectin-1 exerts inhibitory effects during DENV-1 infection

Dengue virus (DENV) is an enveloped RNA virus that is mosquito-transmitted and can infect a variety of immune and non-immune cells. Response to infection ranges from asymptomatic disease to a severe disorder known as dengue hemorrhagic fever. Despite efforts to control the disease, there are no effective treatments or vaccines. In our search for new antiviral compounds to combat infection by dengue virus type 1 (DENV-1), we investigated the role of galectin-1, a widely-expressed mammalian lectin with functions in cell-pathogen interactions and immunoregulatory properties. We found that DENV-1 infection of cells in vitro exhibited caused decreased expression of Gal-1 in several different human cell lines, suggesting that loss of Gal-1 is associated with virus production. In test of this hypothesis we found that exogenous addition of human recombinant Gal-1 (hrGal-1) inhibits the virus production in the three different cell types. This inhibitory effect was dependent on hrGal-1 dimerization and required its carbohydrate recognition domain. Importantly, the inhibition was specific for hrGal-1, since no effect was observed using recombinant human galectin-3. Interestingly, we found that hrGal-1 directly binds to dengue virus and acts, at least in part, during the early stages of DENV-1 infection, by inhibiting viral adsorption and its internalization to target cells. To test the in vivo role of Gal-1 in DENV infection, Gal-1-deficient-mice were used to demonstrate that the expression of endogenous Galectin-1 contributes to resistance of macrophages to in vitro-infection with DENV-1 and it is also important to physiological susceptibility of mice to in vivo infection with DENV-1. These results provide novel insights into the functions of Gal-1 in resistance to DENV infection and suggest that Gal-1 should be explored as a potential antiviral compound.

Phospholipase A2 isolated from the venom of Crotalus durissus terrificus inactivates dengue virus and other enveloped viruses by disrupting the viral envelope

The Flaviviridae family includes several virus pathogens associated with human diseases worldwide. Within this family, Dengue virus is the most serious threat to public health, especially in tropical and sub-tropical regions of the world. Currently, there are no vaccines or specific antiviral drugs against Dengue virus or against most of the viruses of this family. Therefore, the development of vaccines and the discovery of therapeutic compounds against the medically most important flaviviruses remain a global public health priority. We previously showed that phospholipase A₂ isolated from the venom of Crotalus durissus terrificus was able to inhibit Dengue virus and Yellow fever virus infection in Vero cells. Here, we present evidence that phospholipase A₂ has a direct effect on Dengue virus particles, inducing a partial exposure of genomic RNA, which strongly suggests inhibition via the cleavage of glycerophospholipids at the virus lipid bilayer envelope. This cleavage might induce a disruption of the lipid bilayer that causes a destabilization of the E proteins on the virus surface, resulting in inactivation. We show by computational analysis that phospholipase A₂ might gain access to the Dengue virus lipid bilayer through the pores found on each of the twenty 3-fold vertices of the E protein shell on the virus surface. In addition, phospholipase A₂ is able to inactivate other enveloped viruses, highlighting its potential as a natural product lead for developing broad-spectrum antiviral drugs.

Evaluation of four commercial real-time RT-PCR kits for the detection of dengue viruses in clinical samples

Background

Dengue is the most frequent arthropod-borne viral disease worldwide. Because dengue manifestations are similar to those of many other febrile syndromes, the availability of dengue-specific laboratory tests is useful for the differential diagnosis. Timely and accurate diagnosis of dengue virus (DENV) infection is important for appropriate management of complications, pathophysiological studies, epidemiological investigations and optimization of vector-control measures. Several “in-house” reverse transcriptase-polymerase chain reaction (RT-PCR) methods have been developed to detect, type and/or quantify DENV. Standardized dengue RT-PCR kits with internal controls have been recently introduced, but need clinical evaluation. We assessed the performances of 4 commercial DENV real-time RT-PCR kits.

Findings

The 4 kits were evaluated using a panel of 162 samples positive with an existing in-place hemi-nested RT-PCR used for routine DENV-infection diagnosis in patients with acute-febrile disease. The panel included 46 DENV-1, 37 DENV-2, 33 DENV-3, and 46 DENV-4. Also, 70 negative serum specimens were used to determine specificity. Geno-Sen’s Dengue 1–4 Real-Time RT-PCR kit was the only assay to provide quantification using standards, but lacked sensitivity for DENV-4 detection. The Simplexa^TM Dengue RT-PCR assay, with 151 (93.2% [95% confidence interval, 89.3–97.1]) positive samples, had significantly higher sensitivity than the other 3 kits; in a complementary evaluation of 111 consecutive patients’ samples, its performance and genotyping agreed with the hemi-nested gold-standard assay.

Conclusions

The Simplexa^TM Dengue RT-PCR’s good performance to detect and genotype DENV1–4 requires further evaluation in multicenter and prospective studies, particularly in settings of clinical diagnosis during dengue outbreaks.

Development of a TaqMan-based real-time reverse transcription polymerase chain reaction assay for the detection of encephalomyocarditis virus

Encephalomyocarditis virus (EMCV) is one of the major zoonosis pathogens and can cause acute myocarditis in young pigs or reproductive failure in sows. In this study, a TaqMan-based real-time reverse transcription polymerase chain reaction (RT-PCR) assay targeting 3D gene of EMCV was developed and their sensitivities and specificities were investigated. The results indicated that the standard curve had a wide dynamic range (10(1)-10(6) copies/μL) with a linear correlation (R(2)) of 0.996 between the cycle threshold (Ct) value and template concentration. The real-time RT-PCR assay is highly sensitive and able to detect 1.4×10(2) copies/μL of EMCV RNA, as no cross-reaction was observed with other viruses. These data suggested that the real-time RT-PCR assay developed in this study will be suitable for future surveillance and specific diagnosis of EMCV-infection.

Comparison of the FDA-approved CDC DENV-1-4 real-time reverse transcription-PCR with a laboratory-developed assay for dengue virus detection and serotyping

Dengue virus (DENV) is the agent of the most common vector-borne disease worldwide. Using 199 clinical samples collected from Nicaragua and Sri Lanka, a laboratory-developed DENV multiplex real-time reverse transcription-PCR (rRT-PCR) proved more clinically sensitive than the FDA-approved CDC assay for DENV serotypes 1 to 4 when measured against a composite reference standard, with sensitivities of 97.4% versus 87.1%, respectively.

Molecular-level dengue fever diagnostic devices made out of paper

This paper describes the development of nucleic acid detection in paper using a combination of commercial fluorescent probes and DNA ladders, and provides us with a better understanding of the interactions between double-stranded DNA (the amplified products in this study), fiber structures in paper, and fluorescent probes. The amplified products (the reverse-transcription and amplification of dengue virus serotype-2 RNA via RT-LAMP) in this study were subsequently fluorescently labeled in paper-based test zones (on our paper-based diagnostic device), thus fluorescent probes were used to perform the diagnosis of dengue fever, specific to serotype-2.

Environmental influences on antibody-enhanced dengue disease outcomes

Because an enriched environment (EE) enhances T-cell activity and T-lymphocytes contribute to immunopathogenesis during heterologous dengue virus (DENV) infections, we hypothesised that an EE increases dengue severity. To compare single serotype (SS) and antibody-enhanced disease (AED) infections regimens, serial intraperitoneal were performed with DENV3 (genotype III) infected brain homogenate or anti-DENV2 hyperimmune serum followed 24 h later by DENV3 (genotype III) infected brain homogenate. Compared AED for which significant differences were detected between the EE and impoverished environmental (IE) groups (Kaplan-Meyer log-rank test, p = 0.0025), no significant differences were detected between the SS experimental groups (Kaplan-Meyer log-rank test, p = 0.089). Survival curves from EE and IE animals infected with the AED regimen were extended after corticoid injection and this effect was greater in the EE than in the IE group (Kaplan-Meyer log-rank test, p = 0.0162). Under the AED regimen the EE group showed more intense clinical signs than the IE group. Dyspnoea, tremor, hunched posture, ruffled fur, immobility, pre-terminal paralysis, shock and death were associated with dominant T-lymphocytic hyperplasia and presence of viral antigens in the liver and lungs. We propose that the increased expansion of these memory T-cells and serotype cross-reactive antibodies facilitates the infection of these cells by DENV and that these events correlate with disease severity in an EE.

Supercolor coding methods for large-scale multiplexing of biochemical assays

We present a novel method for the encoding and decoding of multiplexed biochemical assays. The method enables a theoretically unlimited number of independent targets to be detected and uniquely identified in any combination in the same sample. For example, the method offers easy access to 12-plex and larger PCR assays, as contrasted to the current 4-plex assays. This advancement would allow for large panels of tests to be run simultaneously in the same sample, saving reagents, time, consumables, and manual labor, while also avoiding the traditional loss of sensitivity due to sample aliquoting. Thus, the presented method is a major technological breakthrough with far-reaching impact on biotechnology, biomedical science, and clinical diagnostics. Herein, we present the mathematical theory behind the method as well as its experimental proof of principle using Taqman PCR on sequences specific to infectious diseases.

Development of an internally controlled real-time reverse transcriptase PCR assay for pan-dengue virus detection and comparison of four molecular dengue virus detection assays

A number of diagnostic tests are available for dengue virus (DENV) detection, including a variety of nucleic acid amplification tests (NAATs). However, reports describing a direct comparison of different NAATs have been limited. In this study, we report the design of an internally controlled real-time reverse transcriptase PCR (rRT-PCR) that detects all four DENV serotypes but does not distinguish between them (the pan-DENV assay). Two hundred clinical samples were then tested using four different DENV RT-PCR assays: the pan-DENV assay, a commercially produced, internally controlled DENV rRT-PCR (the Altona assay), a widely used heminested RT-PCR, and a serotype-specific multiplex rRT-PCR assay. The pan-DENV assay had a linear range extending from 1.0 to 7.0 log10 cDNA equivalents/μl and a lower limit of 95% detection ranging from 1.7 to 7.6 cDNA equivalents/μl, depending on the serotype. When measured against a composite reference standard, the pan-DENV assay proved to be more clinically sensitive than either the Altona or heminested assays, with a sensitivity of 98.0% compared to 72.3% and 78.8%, respectively (P ≤ 0.0001 for both comparisons). The pan-DENV assay detected DENV in significantly more samples collected on or after day 5 of illness and in a subgroup of patients with detectable anti-DENV IgM at presentation. No significant difference in sensitivity was observed between the pan-DENV assay and the multiplex rRT-PCR, despite the presence of an internal control in the former. The detection of DENV RNA late in the course of clinical illness should serve to lengthen the period during which a confirmed molecular diagnosis of DENV infection can be provided.

Diagnosis of dengue: an update

Early diagnosis of dengue, the most common mosquito-borne disease globally, remains challenging. Dengue presents initially as undifferentiated fever, with symptoms becoming more pathognomonic in the later stages of illness. This limits the timeliness in the delivery of appropriate supportive interventions. Laboratory tests are useful for diagnosis although the short-lived viremia and the presence of secondary infection with one of the four heterologous viral serotypes collectively complicate the choice and interpretation of laboratory tests. In this article, the authors review the various approaches for diagnosis of dengue and discuss the appropriate tests to use, including when a dengue vaccine, which is in the late stages of development, is licensed for use. The ensuing reduced dengue prevalence could make diagnosis for vaccine efficacy and escape-mutant monitoring even more challenging.

Comparison of real-time SYBR green dengue assay with real-time taqman RT-PCR dengue assay and the conventional nested PCR for diagnosis of primary and secondary dengue infection

BACKGROUND

Dengue fever and dengue hemorrhagic fever are caused by dengue virus. Dengue infection remains a burning problem of many countries. To diagnose acute dengue in the early phase we improve the low cost, rapid SYBR green real time assay and compared the sensitivity and specificity with real time Taqman(®) assay and conventional nested PCR assay.

AIMS

To develop low cost, rapid and reliable real time SYBR green diagnostic dengue assay and compare with Taqman real-time assay and conventional nested PCR (modified Lanciotti).

MATERIALS AND METHODS

Eight cultured virus strains were diluted in tenth dilution down to undetectable level by the PCR to optimize the primer, temperature (annealing, and extension and to detect the limit of detection of the assay. Hundred and ninety three ELISA and PCR proved dengue clinical samples were tested with real time SYBR(®) Green assay, real time Taqman(®) assay to compare the sensitivity and specificity.

RESULTS

Sensitivity and specificity of real time SYBR® green dengue assay (84% and 66%, respectively) was almost comparable to those (81% and 74%) of Taqman real time PCR dengue assay. Real time SYBR(®) green RT-PCR was equally sensitive in primary and secondary infection while real time Taqman was less sensitive in the secondary infection. Sensitivity of real time Taqman on DENV3 (87%) was equal to SYBR green real time PCR dengue assay.

CONCLUSION

We developed low cost rapid diagnostic SYBR green dengue assay. Further study is needed to make duplex primer assay for the serotyping of dengue virus.

Detection of dengue virus in sera of Brazilian blood donors

BACKGROUND

Dengue is the most important arboviral disease in the world. Dengue viruses (DENVs) have produced huge outbreaks in Brazil in the past 25 years with more than 5 million reported cases. During these epidemics, asymptomatic individuals infected with DENV could donate blood and serve as a source of virus dissemination in the community. Here, we studied the circulation of DENV in healthy individuals during an epidemic outbreak.

STUDY DESIGN AND METHODS

The study included 500 serum samples from healthy blood donors collected at the Hemotherapy Center of Ribeirão Preto, Brazil, during a dengue outbreak. The presence of DENV RNA in the serum samples was screened by real-time reverse transcription-polymerase chain reaction (PCR). The virus serotype was determined by a heminested PCR procedure. A partial fragment of the NS5 gene sequence was used for phylogenetic analysis.

RESULTS

DENV RNA was detected in the serum sample of 2 of 500 (0.4%) individuals. Both of them were infected with DENV-3 Genotype III, a virus that has been circulating in Brazil in the past decade.

CONCLUSION

Individuals with asymptomatic DENV infection can be blood donors and serve as a source of virus dissemination in the community. Further studies are needed to determine the risk of recipient infection by DENV as a result of transfusion in Brazil, especially during epidemic periods.

Nonhematological organ dysfunction and positive fluid balance are important determinants of outcome in adults with severe dengue infection: a multicenter study from India

PURPOSE

The purpose of the study was to explore determinants of outcome in adults with dengue hemorrhagic fever or dengue shock syndrome.

METHODS

We performed a multicenter, retrospective, observational study over a 2-year period in 3 intensive care units (ICUs) in Pune (India).

RESULTS

One hundred eighty-four adult patients were admitted to the ICU with a positive dengue immunoglobulin M test result; 43 met the World Health Organization criteria for dengue hemorrhagic fever or dengue shock syndrome. One patient who was transferred to another hospital and whose outcome was unknown was not included in the analysis. Of the 42 patients, 20 (48%) had multiorgan failure on ICU admission. The ICU mortality was 19% (8/42). Nonsurvivors were more likely than survivors to have cardiovascular (100% vs 12%), respiratory (88% vs 12%), or neurological (75% vs 12%) failure (all P < .01). Hematological failure was not associated with a higher risk of death. Cumulative fluid balance at 72 hours was more positive in nonsurvivors than in survivors (6.2 vs 3.5 L, P < .05). Serum albumin concentrations at ICU admission were lower in nonsurvivors than in survivors (2.9 ± 0.3 vs 3.4 ± 0.7 g/dL, P < .05).

CONCLUSIONS

In our cohort, outcome from severe dengue was primarily related to nonhematological organ failure. Low serum albumin concentration on ICU admission and a more positive fluid balance at 72 hours were also associated with worse outcomes.

Evaluation of two molecular methods for the detection of Yellow fever virus genome

Yellow fever virus (YFV), a member of the family Flaviviridae, genus Flavivirus is endemic to tropical areas of Africa and South America and is among the arboviruses that pose a threat to public health. Recent outbreaks in Brazil, Bolivia, and Paraguay and the observation that vectors capable of transmitting YFV are presenting in urban areas underscore the urgency of improving surveillance and diagnostic methods. Two novel methods (RT-hemi-nested-PCR and SYBR(®) Green qRT-PCR) for efficient detection of YFV strains circulating in South America have been developed. The methods were validated using samples obtained from golden hamsters infected experimentally with wild-type YFV strains as well as human serum and tissue samples with acute disease.

Detection of dengue virus in saliva and urine by real time RT-PCR

Early diagnosis of dengue virus (DENV) infection is important for patient management and control of dengue outbreaks. The objective of this study was to analyze the usefulness of urine and saliva samples for early diagnosis of DENV infection by real time RT-PCR. Two febrile patients, who have been attended at the General Hospital of the School of Medicine of Ribeirao Preto, Sao Paulo University were included in the study. Serum, urine and saliva samples collected from both patients were subjected to real time RT-PCR for DENV detection and quantification. Dengue RNA was detected in serum, urine and saliva samples of both patients. Patient 1 was infected with DENV-2 and patient 2 with DENV-3. Data presented in this study suggest that urine and saliva could be used as alternative samples for early diagnosis of dengue virus infection when blood samples are difficult to obtain, e.g., in newborns and patients with hemorrhagic syndromes.

Genetic diversity of the E protein of dengue type 3 virus

Background

Dengue is the most important arbovirus disease in tropical and subtropical countries. The viral envelope (E) protein is responsible for cell receptor binding and is the main target of neutralizing antibodies. The aim of this study was to analyze the diversity of the E protein gene of DENV-3. E protein gene sequences of 20 new viruses isolated in Ribeirao Preto, Brazil, and 427 sequences retrieved from GenBank were aligned for diversity and phylogenetic analysis.

Results

Comparison of the E protein gene sequences revealed the presence of 47 variable sites distributed in the protein; most of those amino acids changes are located on the viral surface. The phylogenetic analysis showed the distribution of DENV-3 in four genotypes. Genotypes I, II and III revealed internal groups that we have called lineages and sub-lineages. All amino acids that characterize a group (genotype, lineage, or sub-lineage) are located in the 47 variable sites of the E protein.

Conclusion

Our results provide information about the most frequent amino acid changes and diversity of the E protein of DENV-3.