Rapid detection, serotyping and quantitation of dengue viruses by TaqMan real-time one-step RT-PCR

Comprehensive evaluation on progressive development strategies in DENV surveillance and monitoring infection rate among vector population

The elevated rise in dengue infection rate has been a health burden worldwide and it will continue to impact global health for years to come. Accumulated literature holds accountable the geographical expansion of the mosquito species transmitting the dengue virus DENV. The frequency of this viral disease outbreaks has increased rapidly in the recent years, owing to various geo-climatic and anthropological activities. Due to scarcity of any effective control measures, there has been a continuous traceable rise in mortality and morbidity rates. However, it has been reported that the spate of incidences is directly related to density of the virus infected vector (mosquito) population in a given region. In such a scenario, systems capable of detecting virus infected vector population would aid in estimating prediction of outbreak, as well as provide time to deploy suitable management strategies for vector control, and to break the vector-human transmission chain. This would also help in identifying areas, where much improvement is needed for vector management. To this context, we illustrate an exhaustive overview of both gold standards and as well as emerging advents for sensitive and specific mosquito population strategized viral detection technologies. We summarize the cutting-edge technologies and the challenges faced in pioneering to field application. Regardless the proven popularity of the gold standards for detection purpose, they offer certain limitations. Thus with the surge in the infection rate globally, approaches for development of newer advancements and technique upgradation to arrest the infection escalation and for early detection as a part of vector management should be prioritized.

Innovations in dengue virus detection: An overview of conventional and electrochemical biosensor approaches

Globally, people are in great threat due to the highly spreading of viral infectious diseases. Every year like 100-300 million cases of infections are found, and among them, above 80% are not recognized and irrelevant. Dengue virus (DENV) is an arbovirus infection that currently infects people most frequently. DENV encompasses four viral serotypes, and they each express comparable sign. From a mild febrile sickness to a potentially fatal dengue hemorrhagic fever, dengue can induce a variety of symptoms. Presently, the globe is being challenged by the untimely identification of dengue infection. Therefore, this review summarizes advances in the detection of dengue from conventional methods (nucleic acid-based, polymerase chain reaction-based, and serological approaches) to novel biosensors. This work illustrates an extensive study of the current designs and fabrication approaches involved in the formation of electrochemical biosensors for untimely identifications of dengue. Additionally, in electrochemical sensing of DENV, we skimmed through significances of biorecognition molecules like lectins, nucleic acid, and antibodies. The introduction of emerging techniques such as the CRISPR/Cas' system and their integration with biosensing platforms has also been summarized. Furthermore, the review revealed the importance of electrochemical approach compared with traditional diagnostic methods.

Exposure to Zika and chikungunya viruses impacts aspects of the vectorial capacity of Aedes aegypti and Culex quinquefasciatus

Zika (ZIKV) and chikungunya (CHIKV) are arboviruses that cause infections in humans and can cause clinical complications, representing a worldwide public health problem. Aedes aegypti is the primary vector of these pathogens and Culex quinquefasciatus may be a potential ZIKV vector. This study aimed to evaluate fecundity, fertility, survival, longevity, and blood feeding activity in Ae. aegypti after exposure to ZIKV and CHIKV and, in Cx. quinquefasciatus exposed to ZIKV. Three colonies were evaluated: AeCamp (Ae. aegypti-field), RecL (Ae. aegypti-laboratory) and CqSLab (Cx. quinquefasciatus-laboratory). Seven to 10 days-old females from these colonies were exposed to artificial blood feeding with CHIKV or ZIKV. CHIKV caused reduction in fecundity and fertility in AeCamp and reduction in survival and fertility in RecL. ZIKV impacted survival in RecL, fertility in AeCamp and, fecundity and fertility in CqSLab. Both viruses had no effect on blood feeding activity. These results show that CHIKV produces a higher biological cost in Ae. aegypti, compared to ZIKV, and ZIKV differently alters the biological performance in colonies of Ae. aegypti and Cx. quinquefasciatus. These results provide a better understanding over the processes of virus-vector interaction and can shed light on the complexity of arbovirus transmission.

Diagnostic approaches for dengue infection

INTRODUCTION

Every year, a significant rise in dengue incidence observed is responsible for 10% of fever episodes in children and adolescents in endemic countries. Considering that the symptoms of dengue are similar to those of many other viruses, early diagnosis of the disease has long been difficult, and lack of sensitive diagnostic tools may be another factor contributing to a rise in dengue incidence.

AREAS COVERED

This review will highlight dengue diagnostics strategies and discuss other possible targets for dengue diagnosis. Understanding the dynamics of the immune response and how it affects viral infection has enabled informed diagnosis. As more technologies emerge, precise assays that include some clinical markers need to be included.

EXPERT OPINION

Future diagnostic strategies will require the use both viral and clinical markers in a serial manner with the use of artificial intelligence technology to determine from the first point of illness to better determine severity status and management. A definitive endpoint is not in the horizon as the disease as well as the virus is constantly evolving and hence many developed assays need to be constantly changing some of their reagents periodically as newer genotypes and probably too serotypes emerge.

A simplified viral RNA extraction method based on magnetic nanoparticles for fast and high-throughput detection of SARS-CoV-2

The ongoing outbreak of the novel coronavirus disease 2019 (COVID-19) draws worldwide concerns due to its long incubation period and strong infectivity. Although RT-PCR-based methods are being widely applied for clinical diagnosis, timely and accurate diagnosis towards COVID-19 causing virus, the SARS-CoV-2, is still limited due to labor-intensive and time-consuming operations. Herein, we report a new viral RNA extraction method based on poly-(amino ester) with carboxyl group (PC)-coated magnetic nanoparticles (pcMNPs) for the sensitive detection of SARS-CoV-2. This method combines the lysis and binding steps into one step, and refines multiple washing steps into one step, giving a turnaround time of less than 9 min. Furthermore, the extracted pcMNP-RNA complexes can be directly introduced into subsequent RT-PCR reactions without elution. This simplified viral RNA method could be well adapted in fast manual and automated high-throughput nucleic acids extraction protocols suitable for different scenarios. A high sensitivity down to 100 copies/mL and a linear correlation between 100 and 10⁶ copies/mL of SARS-CoV-2 pseudovirus particles are achieved in both protocols. Benefitting from the simplicity and excellent performances, this new method can dramatically improve the efficiency and reduce operational requirements for the early clinical diagnosis and large-scale SARS-CoV-2 nucleic acid screening.

Dynamic of Mayaro Virus Transmission in Aedes aegypti, Culex quinquefasciatus Mosquitoes, and a Mice Model

Mayaro virus (MAYV) is transmitted by Haemagogus spp. mosquitoes and has been circulating in Amazon areas in the North and Central West regions of Brazil since the 1980s, with an increase in human case notifications in the last 10 years. MAYV introduction in urban areas is a public health concern as infections can cause severe symptoms similar to other alphaviruses. Studies with Aedes aegypti have demonstrated the potential vector competence of the species and the detection of MAYV in urban populations of mosquitoes. Considering the two most abundant urban mosquito species in Brazil, we investigated the dynamics of MAYV transmission by Ae. aegypti and Culex quinquefasciatus in a mice model. Mosquito colonies were artificially fed with blood containing MAYV and infection (IR) and dissemination rates (DR) were evaluated. On the 7th day post-infection (dpi), IFNAR BL/6 mice were made available as a blood source to both mosquito species. After the appearance of clinical signs of infection, a second blood feeding was performed with a new group of non-infected mosquitoes. RT-qPCR and plaque assays were carried out with animal and mosquito tissues to determine IR and DR. For Ae. aegypti, we found an IR of 97.5-100% and a DR reached 100% in both 7 and 14 dpi. While IR and DR for Cx. quinquefasciatus was 13.1-14.81% and 60% to 80%, respectively. A total of 18 mice were used (test = 12 and control = 6) for Ae. aegypti and 12 (test = 8 and control = 4) for Cx. quinquefasciatus to evaluate the mosquito-mice transmission rate. All mice that were bitten by infected Ae. aegypti showed clinical signs of infection while all mice exposed to infected Cx. quinquefasciatus mosquitoes remained healthy. Viremia in the mice from Ae. aegypti group ranged from 2.5 × 10⁸ to 5 × 10⁹ PFU/mL. Ae. aegypti from the second blood feeding showed a 50% IR. Our study showed the applicability of an efficient model to complete arbovirus transmission cycle studies and suggests that the Ae. aegypti population evaluated is a competent vector for MAYV, while highlighting the vectorial capacity of Ae. aegypti and the possible introduction into urban areas. The mice model employed here is an important tool for arthropod-vector transmission studies with laboratory and field mosquito populations, as well as with other arboviruses.

Potential Nosocomial Infections by the Zika and Chikungunya Viruses in Public Health Facilities in the Metropolitan Area of Recife, Brazil

Since 2015, the Dengue, Zika, and Chikungunya viruses gained notoriety for their impact in public health in many parts of the globe, including Brazil. In Recife, the capital of Pernambuco State, the introduction of ZIKV impacted human population tremendously, owing to the increase in the number of neurological cases, such as the Guillain−Barré and congenital Zika disorders. Later, Recife was considered to be the epicenter for ZIKV epidemics in Brazil. For arboviral diseases, there are some risk factors, such as climate changes, low socioeconomic conditions, and the high densities of vectors populations, that favor the broad and rapid dispersion of these three viruses in the city. Therefore, continuous arbovirus surveillance provides an important tool for detecting these arboviruses and predicting new outbreaks. The purpose of the present study was to evaluate the circulation of DENV, ZIKV, and CHIKV by RT-qPCR in mosquitoes collected in health care units from the metropolitan area of Recife (MAR), during 2018. A total of 2321 female mosquitoes (357 pools) belonging to two species, Aedes aegypti and Culex quinquefasciatus, were collected from 18 different healthcare units, distributed in five cities from the MAR. Twenty-three pools were positive for ZIKV, out of which, seventeen were of C. quinquefasciatus and six were of A. aegypti. Positive pools were collected in 11/18 health care units screened, with Cq values ranging from 30.0 to 37.4 and viral loads varying from 1.88 × 107 to 2.14 × 109 RNA copies/mL. Nosocomial Aedes- and Culex-borne transmission of arbovirus are widely ignored by surveillance and vector control programs, even though healthcare-associated infections (HAI) are considered a serious threat to patient safety worldwide. Although the results presented here concern only the epidemiological scenario from 2018 in MAR, the potential of hospital-acquired transmission through mosquito bites is being overlooked by public health authorities. It is, therefore, of the ultimate importance to establish specific control programs for these locations.

Dengue Infection - Recent Advances in Disease Pathogenesis in the Era of COVID-19

The dynamics of host-virus interactions, and impairment of the host’s immune surveillance by dengue virus (DENV) serotypes largely remain ambiguous. Several experimental and preclinical studies have demonstrated how the virus brings about severe disease by activating immune cells and other key elements of the inflammatory cascade. Plasmablasts are activated during primary and secondary infections, and play a determinative role in severe dengue. The cross-reactivity of DENV immune responses with other flaviviruses can have implications both for cross-protection and severity of disease. The consequences of a cross-reactivity between DENV and anti-SARS-CoV-2 responses are highly relevant in endemic areas. Here, we review the latest progress in the understanding of dengue immunopathogenesis and provide suggestions to the development of target strategies against dengue.

Development of a Singleplex Real-Time Reverse Transcriptase PCR Assay for Pan-Dengue Virus Detection and Quantification

Dengue virus (DENV) infection is a significant global health problem. There are no specific therapeutics or widely available vaccines. Early diagnosis is critical for patient management. Viral RNA detection by multiplex RT-PCR using multiple pairs of primers/probes allowing the simultaneous detection of all four DENV serotypes is commonly used. However, increasing the number of primers in the RT-PCR reaction reduces the sensitivity of detection due to the increased possibility of primer dimer formation. Here, a one tube, singleplex real-time RT-PCR specific to DENV 3′-UTR was developed for the detection and quantification of pan-DENV with no cross reactivity to other flaviviruses. The sensitivity of DENV detection was as high as 96.9% in clinical specimens collected at the first day of hospitalization. Our assay provided equivalent PCR efficiency and RNA quantification among each DENV serotype. The assay’s performance was comparable with previously established real-time RT-PCR targeting coding sequences. Using both assays on the same specimens, our results indicate the presence of defective virus particles in the circulation of patients infected with all serotypes. Dual regions targeting RT-PCR enhanced the sensitivity of viral genome detection especially during the late acute phase when viremia rapidly decline and an incomplete viral genome was clinically evident.

Arbovirus Surveillance in Field-Collected Mosquitoes From Pernambuco-Brazil, During the Triple Dengue, Zika and Chikungunya Outbreak of 2015-2017

The (re) emergence of arboviruses around the world is a public health concern once severe outbreaks are usually associated with these infections. The co-circulation of Dengue (DENV), Zika (ZIKV) and Chikungunya (CHIKV) viruses in the past few years has caused a unique epidemic situation in Brazil. The northeast region of the country was the most affected by clinical complications from such arboviruses’ infections, including neurological disorders caused by ZIKV. In this particular region, Aedes mosquitoes are the main vectors of DENV, ZIKV and CHIKV, with Culex quinquefasciatus also considered as a potential vector of ZIKV. Therefore, virological surveillance in mosquitoes contributes to understanding the epidemiological profile of these diseases. Here, we report the circulation of DENV, ZIKV and CHIKV in Aedes spp. and Cx. quinquefasciatus female mosquitoes collected in areas with a high arbovirus circulation in humans in the Metropolitan Region of Recife, Pernambuco, Brazil, during the triple-epidemics of 2015-17. All the field-caught mosquitoes were sent to the laboratory for arbovirus screening after RNA extraction and RT-PCR/RT-qPCR. A total of 6,227 females were evaluated and, as a result, DENV, ZIKV and CHIKV were identified in Ae. aegypti, Ae. taeniorhynchus and Cx. quinquefasciatus mosquito pools. In addition, DENV and ZIKV were isolated in C6/36 cells. In conclusion, it is important to highlight that arbovirus surveillance performed in mosquitoes from DENV-ZIKV-CHIKV hotspots areas can serve as an early-warning system to target vector control actions more efficiently in each studied area.

G-quadruplex microspheres-based optical RNA biosensor for arthropod-borne virus pathogen detection: A proof-of-concept with dengue serotype 2

Dengue virus (DENV) is a positive-sense single-stranded RNA virus and that the detection of viral RNA itself is highly desirable, which can be achieved by using RNA biosensor diagnostic method. Herein, acrylic micropolymer-based optical RNA biosensor was developed by binding anionic copper(II) phthalocyanine (CPC) planar aromatic ligand to the G-quadruplex DNA probe via end-stacking with π-system of the guanine (G) quartet, and a blue coloration was developed on the G-quadruplex microspheres. Hybridization of G-quadruplex DNA probe with target DENV serotype 2 (DENV2) RNA unfolded the G-quadruplex, and rendering release of the CPC planar optical label, causing discoloration of the G-quadruplex microbiosensor. Optical characterization of the RNA biosensor was performed by means of fiber optic reflectance spectrophotometer at maximum reflectance wavelength of 774 nm. The reflectance response enhancement of the RNA-responsive G-quadruplex-based reflectometric biosensor was linearly proportional to the target oligo DENV2 RNA concentration in the range of 2 zM-2 μM, with a 0.447 zM limit of detection and a rapid response time of 30 min. Heightening in the reflectance signal based on structural transition of G-quadruplex in response to target RNA was successfully implemented in real-time DENV2 detection in non-invasive human fluid samples (i.e. saliva and urine) under informed consent.

Molecular Diagnosis of Dengue

Several protocols for genomic amplification using reverse transcription followed by polymerase chain reaction (RT-PCR), important in the identification of the infecting serotype, have been used in the rapid diagnosis of Dengue Virus (DENV) infections. The qualitative protocol described by Lanciotti et al. (J Clin Microbiol 30: 545-551, 1992) suggested by WHO detects the four DENV serotypes simultaneously in one procedure "semi-nested," generating amplified products with specific sizes in base pairs for each serotype and it has been the most used in the past two decades. However, advances in molecular diagnosis have enabled the development of RT-PCR in real time (qRT-PCR) based on the use of dyes and probes (SYBR green and TaqMan), which is performed in a single step and is capable of providing quantitative data. In addition to quantification, the advantages of qRT-PCR over conventional RT-PCR include speed, greater sensitivity and specificity, and low rate of false positives. Several protocols for the diagnosis and/or quantification of DENV have already been described. Non-PCR-based methods such as reverse transcription loop-mediated isothermal amplification have shown high sensitivities and specificities. RT-PCR and qRT-PCR techniques can be performed using serum, plasma, infected cells, mosquitoes, fresh, and paraffin-embedded tissues. However, despite fast and accurate, they are limited to samples collected during the acute phase of infection (up to 7 days after the onset of symptoms) and require specialized equipment and trained staff.

Aedes aegypti continuously exposed to Bacillus thuringiensis svar. israelensis does not exhibit changes in life traits but displays increased susceptibility for Zika virus

Background

Aedes aegypti can transmit arboviruses worldwide, and Bacillus thuringiensis svar. israelensis (Bti)-based larvicides represent an effective tool for controlling this species. The safety of Bti and lack of resistance have been widely reported; however, little is known regarding the impact of the extensive use of these larvicides on the life traits of mosquitoes. Therefore, this study investigated biological parameters, including susceptibility to arbovirus, of an Ae. aegypti strain (RecBti) subjected to 29 generations of exposure to Bti compared with the RecL reference strain.

Methods

The biological parameters of individuals reared under controlled conditions were compared. Also, the viral susceptibility of females not exposed to Bti during their larval stage was analysed by oral infection and followed until 14 or 21 days post-infection (dpi).

Results

RecBti individuals did not display alterations in the traits that were assessed (fecundity, fertility, pupal weight, developmental time, emergence rate, sex ratio and haematophagic capacity) compared to RecL individuals. Females from both strains were susceptible to dengue serotype 2 (DENV-2) and Zika virus (ZIKV). However, RecBti females showed significantly higher rates of ZIKV infection compared with RecL females at 7 (90% versus 68%, Chi-square: χ² = 7.27, df = 1, P = 0.006) and 14 dpi (100% versus 87%, Chi-square: χ² = 7.69, df = 1, P = 0.005) and for dissemination at 7 dpi (83.3% versus 36%, Fisher’s exact test: P < 0.0001, OR = 0.11, 95% CI 0.03–0.32). Quantification of DENV-2 and ZIKV viral particles produced statistically similar results for females from both strains.

Conclusions

Prolonged exposure of Ae. aegypti larvae to Bti did not alter most of the evaluated biological parameters, except that RecBti females exhibited a higher vector susceptibility for ZIKV. This finding is related to a background of Bti exposure for several generations but not to a previous exposure of the tested females during the larval stage. This study highlights mosquito responses that could be associated with the chronic exposure to Bti in addition to the primary larvicidal effect elicited by this control agent.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04880-6.

Molecular and Haematological Analysis of Dengue Virus-3 Among Children in Lahore, Pakistan

Background: Dengue virus (DENV) is an RNA virus belonging to the family Flaviviridae of the genus Flavivirus with worldwide distribution. Dengue fever is caused by any of four closely-related serotypes DENV, an emerging pandemic-prone viral disease in many regions of the world. Objectives: The present study aimed to determine the prevalence of dengue virus genotypes and serotypes in children aged below 15 years in Lahore, Pakistan. Methods: In this study, 112 serum samples were collected from clinically suspected dengue fever patients from March 2017 to December 2018 at different tertiary care hospitals in Lahore, Pakistan. Regarding the patients’ age, the samples were divided into four groups from A to D (i.e., 0 - 1, 1 - 5, 5 - 10, and 10 - 15 years of age). Rapid immuno-chromatography (ICT) test was conducted on the collected serum samples, followed by quantitative RT-PCR for serotype of dengue virus. Results: Out of 112 samples, 34 samples were diagnosed as DENV positive by the rapid ICT screening method. No virus was detected in groups A and B, while three samples were positive in group C (1 boy and two girls), and 31 samples (23 boys and 8 girls) were positive in group D. The results of quantitative RT-PCR exclusively showed DEN-3 serotype in all the ICT positive samples. The results indicated that the prevalence of DEN-3 serotype in children was 100%, indicating that DEN-3 serotype might cause severe epidemics in the future in Lahore, Pakistan. Hematological analysis revealed an increase in hematocrits in 41.1% dengue-positive cases. Leucopenia was prominent in 79.4% of the cases, while Thrombocytopenia was reported in 70.5% of the participants. The biochemical analysis also indicated an increase in liver enzymes in patients (ALT 88%, AST 79%), while the lower levels of cholesterol (69 %) and serum albumin (25%) were also observed. Conclusions: Dengue virus spreads and grows quickly worldwide over a highly short time interval. Dengue fever claims for a significant number of lives. This study would help individuals know about the status of laboratory parameters in dengue fever and detect how to overcome the prevalence of Dengue virus.

Management of Coronavirus Disease 2019 (COVID-19) Pandemic: From Diagnosis to Treatment Strategies

Following the emergence of severe acute respiratory syndrome (SARS) in 2002 and the Middle East respiratory syndrome (MERS) in 2012, the world is now combating a third large-scale outbreak caused by a coronavirus, the coronavirus disease 2019 (COVID-19). After the rapid spread of SARS-coronavirus (CoV)-2 (the virus causing COVID-19) from its origin in China, the World Health Organization (WHO) declared a Public Health Emergency of International Concern (PHEIC) on January 30, 2020. From the beginning of the COVID-19 pandemic, a significant number of studies have been conducted to better understand the biology and pathogenesis of the novel coronavirus, and to aid in developing effective treatment regimens, therapeutics, and vaccines. This review focuses on the recent advancements in the rapidly evolving areas of clinical care and management of COVID-19. The emerging strategies for the diagnosis and treatment of this disease are explored, and the development of effective vaccines is reviewed.

Identification of the phytobioactive Polygonum cuspidatum as an antiviral source for restricting dengue virus entry

Dengue virus (DENV) is a mosquito-borne pathogen that is becoming a serious global threat, owing to its rising incidence in inter-tropical regions that yield over 50 million annual infections. There are currently no approved antiviral agents for the management of dengue, and recent shortcomings in its immunization called for immediate action to develop effective drugs with prophylactic ability to better manage its infection. In an attempt to discover novel antiviral sources, we identified the medicinal herb Polygonum cuspidatum (PC) as a bioactive botanical material against DENV infectivity. Specifically, the methanolic extract from PC rhizomes (PCME) potently inhibited DENV infection without causing significant cytotoxicity. Further examination on the viral life cycle demonstrated that PCME particularly targeted the initial stages of DENV infection, while pre- and post-infection treatments had no effect. More importantly, the PCME could efficiently inactivate DENV free virus particles and block the viral attachment and entry/fusion events without apparently influencing viral replication, egress, and cell-to-cell spread. The antiviral effect of PCME was also recapitulated in infection analysis using DENV pseudoparticles displaying viral structural proteins that mediate DENV particle entry. Besides, PCME treatment also inhibited direct DENV entry into several cell types relevant to its infection and reduced viral infectivity of other members of the Flaviviridae family, including the hepatitis C virus (HCV) and Zika virus (ZIKV). Due to its potency against DENV entry, we suggest that the phytobioactive extract from PC is an excellent starting point as an antiviral source material for further development of therapeutic strategies in the prophylactic management of DENV infection.

IoT PCR for pandemic disease detection and its spread monitoring

During infectious disease outbreaks, the centers for disease control need to monitor particular areas. Considerable effort has been invested in the development of portable, user-friendly, and cost-effective systems for point-of-care (POC) diagnostics, which could also create an Internet of Things (IoT) for healthcare via a global network. However, at present IoT based on a functional POC instrument is not available. Here we show a fast, user-friendly, and affordable IoT system based on a miniaturized polymerase chain reaction device. We demonstrated the system's capability by amplification of complementary deoxyribonucleic acid (cDNA) of the dengue fever virus. The resulting data were then automatically uploaded via a Bluetooth interface to an Android-based smartphone and then wirelessly sent to a global network, instantly making the test results available anywhere in the world. The IoT system presented here could become an essential tool for healthcare centers to tackle infectious disease outbreaks identified either by DNA or ribonucleic acid.

Sylvatic dengue virus type 4 in Aedes aegypti and Aedes albopictus mosquitoes in an urban setting in Peninsular Malaysia

Dengue fever is endemic in Malaysia, contributing to significant economic and health burden in the country. Aedes aegypti and Ae. albopictus are the main vectors of the dengue virus (DENV), which circulates in sylvatic and human transmission cycles and has been present in Malaysia for decades. The study investigated the presence and distribution of DENV in urban localities in the Klang Valley, Peninsular Malaysia. A total of 364 Ae. aegypti and 1,025 Ae. albopictus larvae, and 10 Ae. aegypti and 42 Ae. albopictus adult mosquitoes were screened for the presence of DENV. In total, 31 (2.2%) samples were positive, of which 2 Ae. albopictus larvae were co-infected with two serotypes, one with DENV-2 and DENV-3 and the other with DENV-3 and DENV-4. Phylogenetic analysis determined that the isolates belonged to DENV-1 genotype I (1 Ae. aegypti adult), DENV-2 (1 Ae. albopictus larva), DENV-3 genotype V (3 Ae. aegypti larvae and 10 Ae. albopictus larvae) and DENV-4 genotype IV (6 Ae. aegypti larvae and 12 Ae. albopictus larvae), a sylvatic strain of DENV-4 which was most closely related with sylvatic strains isolated from arboreal mosquitoes and sentinel monkeys in Peninsular Malaysia in the 1970s. All four DENV serotypes were co-circulating throughout the study period. The detection of a sylvatic strain of DENV-4 in Ae. aegypti and Ae. albopictus mosquitoes in urban areas in Peninsular Malaysia highlights the susceptibility of these vectors to infection with sylvatic DENV. The infectivity and vector competence of these urban mosquitoes to this strain of the virus needs further investigation, as well as the possibility of the emergence of sylvatic virus into the human transmission cycle.

Anti-viral activity of culinary and medicinal mushroom extracts against dengue virus serotype 2: an in-vitro study

BACKGROUND

Dengue is a mosquito-borne viral infection that has become a major public health concern worldwide. Presently, there is no specific vaccine or treatment available for dengue viral infection.

METHODS

Lignosus rhinocerotis, Pleurotus giganteus, Hericium erinaceus, Schizophyllum commune and Ganoderma lucidium were selected for evaluation of their in-vitro anti-dengue virus serotype 2 (DENV-2) activities. Hot aqueous extracts (HAEs), ethanol extracts (EEs), hexane soluble extracts (HSEs), ethyl acetate soluble extracts (ESEs) and aqueous soluble extracts (ASEs) were prepared from the selected mushrooms. The cytotoxic effects of the extracts were evaluated by the MTT assay. The anti-DENV-2 activities of the extracts were evaluated in three different assays: simultaneous, attachment and penetration assays were perfomed using plaque reduction assays and RT-qPCR assays. The effect of the addition time on viral replication was assessed by the time of addition assay, and a virucidal assay was carried out to evaluate the direct effect of each mushroom extract on DENV-2. The chemical composition of glucans, and the protein and phenolic acid contents in the extracts were estimated.

RESULTS

We found that the HAEs and ASEs of L. rhinocerotis, P. giganteus, H. erinaceus and S. commune were the least toxic to Vero cells and showed very prominent anti-DENV2 activity. The 50% inhibitory concentration (IC₅₀) values of the ASEs ranged between 399.2-637.9 μg/ml, while for the HAEs the range was 312.9-680.6 μg/ml during simultaneous treatment. Significant anti-dengue activity was also detected in the penetration assay of ASEs (IC₅₀: 226.3-315.4 μg/ml) and HAEs (IC₅₀: 943.1-2080.2 μg/ml). Similarly, we observed a marked reduction in the expression levels of the ENV and NS5 genes in the simultaneous and penetration assays of the ASEs and HAEs. Time-of-addition experiments showed that the highest percent of anti-DENV2 activity was observed when the mushroom extracts were added immediately after virus adsorption. None of the extracts exhibited virucidal effect. Chemical composition analysis showed that the major components in the mushroom HAEs and ASEs were glucan (beta D-glucan) and proteins, however, there was no significant correlation between the anti-dengue activity and the concentration of glucans and proteins.

CONCLUSION

These findings demonstrated the potential of mushroom extracts as anti-dengue therapeutic agents with less toxic effects.

Electrochemical biosensing of mosquito-borne viral disease, dengue: A review

Dengue virus is a mosquito-borne, single positive-stranded RNA virus that spread human being through infected female Aedes mosquito bite and causes dengue fever. The demand for early detection of this virus has increased to control the widespread of infectious diseases and protect humankind from its harmful effects. Recently, biosensors are found to the potential tool to detect and quantify the virus with fast detection, relatively cost-effective, high sensitivity and selectivity than the conventional diagnostic methods such as immunological and molecular techniques. Mostly, the biosensors employ electrochemical detection technique with transducers, owing to its easy construction, low-cost, ease of use, and portability. Here, we review the current trends and advancement in the electrochemical diagnosis of dengue virus and discussed various types of electrochemical biosensing techniques such as; amperometric, potentiometric, impedometric, and voltammetric sensing. Apart from these, we discussed the role of biorecognition molecules such as nucleic acid, antibodies, and lectins in electrochemical sensing of dengue virus. In addition, the review highlighted the benefits of the electrochemical approach in comparison with traditional diagnostic methods. We expect that these dengue virus diagnostic techniques will continue to evolve and grow in future, with exciting new possibilities stemming from advancement in the rational design of electrochemical biosensors.

Molecular Characterization of Dengue E/NS1 Junction Genotype 2 Isolated From Saudi Patients, Jeddah Province

BACKGROUND AND OBJECTIVE

Dengue is the most important arthropod-borne viral disease which caused by the four-dengue virus serotypes (1-4) and its incidence has grown dramatically around the world in the recent decades. This study was conducted to determine the molecular characterization of dengue virus genotypes spreading in Jeddah province.

METHODOLOGY

To distinguish dengue virus genotypes, serum samples from 13 infected patients were subjected to envelop and non-structural 1 (E/NS1) gene amplification and sequence analysis at the nucleotide and amino acid levels.

RESULTS

The present partial dengue virus phylogenetic analysis announced the domination of dengue virus 2 genotype among the current dengue virus samples circulating in Jeddah province. Dengue virus 2 current isolates were grouped in one branch and seemed to be more closely related to various strains isolated from Sri-Lanka, Australia and Singapore and confirmed by internucleotide distance average ranged +/-0.01. Interestingly, sequences analysis of amino acids confirmed substitution of 8 amino acid residue (Ser729Gua, Ser729Arg, Val762Gau, Val780phe, Val781Leu, Val781Ala, Glu858Asp and Gln873His) among the present isolates comparing with previous references strains isolated from different countries. Remarkably, one unique amino acid residue Ala741Val was verified in the 10 present isolates compared to the reference sequence previously isolated from Jeddah.

CONCLUSION

Notably, the present study demonstrated the sequencing analysis of the dengue virus 2-E/NS1 on both nucleotide and amino acid levels and confirmed its endogenously prevalence in Jeddah.

Application of whole genome data for in silico evaluation of primers and probes routinely employed for the detection of viral species by RT-qPCR using dengue virus as a case study

Background

Viral infection by dengue virus is a major public health problem in tropical countries. Early diagnosis and detection are increasingly based on quantitative reverse transcriptase real-time polymerase chain reaction (RT-qPCR) directed against genomic regions conserved between different isolates. Genetic variation can however result in mismatches of primers and probes with their targeted nucleic acid regions. Whole genome sequencing allows to characterize and track such changes, which in turn enables to evaluate, optimize, and (re-)design novel and existing RT-qPCR methods. The immense amount of available sequence data renders this however a labour-intensive and complex task.

Results

We present a bioinformatics approach that enables in silico evaluation of primers and probes intended for routinely employed RT-qPCR methods. This approach is based on analysing large amounts of publically available whole genome data, by first employing BLASTN to mine the genomic regions targeted by the RT-qPCR method(s), and afterwards using BLASTN-SHORT to evaluate whether primers and probes will anneal based on a set of simple in silico criteria. Using dengue virus as a case study, we evaluated 18 published RT-qPCR methods using more than 3000 publically available genomes in the NCBI Virus Variation Resource, and provide a systematic overview of method performance based on in silico sensitivity and specificity.

Conclusions

We provide a comprehensive overview of dengue virus RT-qPCR method performance that will aid appropriate method selection allowing to take specific measures that aim to contain and prevent viral spread in afflicted regions. Notably, we find that primer-template mismatches at their 3′ end may represent a general issue for dengue virus RT-qPCR detection methods that merits more attention in their development process. Our approach is also available as a public tool, and demonstrates how utilizing genomic data can provide meaningful insights in an applied public health setting such as the detection of viral species in human diagnostics.

Electronic supplementary material

The online version of this article (10.1186/s12859-018-2313-0) contains supplementary material, which is available to authorized users.

DNA Switch: Toehold-Mediated DNA Isothermal Amplification for Dengue Serotyping

The inherent ability of nucleic acids to recognize a complementary pair has gained wide popularity in DNA sensor applications. DNA molecules can be produced in bulk and easily incorporated with various nanomaterials for sensing applications. More complex designs and sophisticated DNA sensors have been reported over the years to allow DNA detection in a faster, cheaper, and more convenient manner. Here, we report a DNA sensor designed to function like a switch to turn “on” silver nanocluster (AgNC) generation in the presence of a specific DNA target. By defining the probe region sequence, we are able to tune the color of the AgNC generated in direct relation to the different targets. As a proof of concept, we used dengue RNA-dependent RNA polymerase conserved sequences from all four serotypes as targets. This method was able to distinguish each dengue serotype by generating the serotype-respective AgNCs. The DNA switch was also able to identify and amplify the correct target in a mixture of targets with good specificity. This strategy has a detection limit of between 1.5 and 2.0 µM depending on the sequence of AgNC. The DNA switch approach provides an attractive alternative for single-target or multiplex DNA detection.

Shared IgG Infection Signatures vs. Hemorrhage-Restricted IgA Clusters in Human Dengue: A Phenotype of Differential Class-Switch via TGFβ1

Phenotypic manifestations of infectious diseases are closely related to individual immune responses. Methods to extract information from patients' own immune reactions would be of great use for both diagnosis and treatment. Dengue fever is one of the diseases that clinical aggravations could occur paradoxically after humoral immunity appears. This property makes dengue fever an excellent disease model to explore. A principal component analyses (PCAs)-based framework derived from a prior vaccination study was developed. The framework was verified by successful demonstrations of known IgG signatures from a Mexico Dengue data set. Afterward the pipeline was tested upon de novo IgG and IgA libraries of Dengue patients from southern Taiwan. We discovered four infection signatures within IgG repertoires, two of which were identical to previous reports. However, it was IgA but not IgG that could differentiate hemorrhagic from non-hemorrhagic patients. IgA repertoires were found more diversified among bleeders, from whom seven signature clusters were characterized. The expressions of transforming growth factor beta 1 (TGFβ1) and accordingly mediated class-switch activity of IgA were distinct only among the PCA-segregated bleeding group. In sum, intercontinental sharing of IgG signatures in dengue fever was demonstrated via a unified working flow. Differential regulation of IgA class-switch with associated diversity expansion plus existences of hemorrhage-restricted clusters were shown. The ability of the framework to find common IgG signatures would implicate applications to infections even from unknown pathogens. The clusters within IgA repertoires could offer perspectives to other IgA-related bleeding disorders such as Henoch-Schönlein purpura or IgA nephropathy. Substantiated grounds for IgA-specific effector function via TGFβ1-mediated class-switch would be a new factor to consider for infectious diseases.

Comparison of Zika virus (ZIKV) RNA detection in plasma, whole blood and urine - Case series of travel-associated ZIKV infection imported to Italy, 2016

OBJECTIVES

The capability to detect ZIKV RNA is of crucial importance for cases confirmation. However, due to the short-lived viremia, the detection of ZIKV RNA in plasma/serum is challenging for samples collected more than one week after onset of clinical illness. We compared the window time and detection rate of ZIKV RNA in different specimen types (plasma, whole blood and urine) collected simultaneously at several times post-symptom onset.

METHODS

We examined the presence of ZIKV RNA in matched specimens of whole blood, plasma and urine collected in the same date (3-28 days after symptom onset) from 10 ZIKV infected patients.

RESULTS

ZIKV RNA was found in plasma as late as 10 days after symptoms onset and tested positive in all 5 (100%) and in 2 of 6 (33,3%) plasma samples collected 1-5 and 6-10 days after symptoms onset, respectively. ZIKV RNA was positive in urine through the 21st day after symptom onset; the detection rate of ZIKV RNA in urine samples was 100% (11/11) for samples collected 1-10 days from symptoms onset, decreasing at later times of sampling. The detection rate of ZIKV RNA in whole blood was comparable to that in urine samples but extended the window of detection of ZIKV RNA up to 26 days after symptom onset.

CONCLUSIONS

Our results highlight the usefulness of simultaneously testing multiple specimen types in order to extend the rate and the time frame of ZIKV RNA detection, increasing the possibility of cases confirmation through direct diagnosis in convalescence-phase of infection, supplementing serological data which are often difficult to interpret.

Kinetic analysis of IgM monoclonal antibodies for determination of dengue sample concentration using SPR technique

Surface plasmon resonance (SPR) sensing is recently emerging as a valuable technique for measuring the binding constants, association and dissociation rate constants, and stoichimetry for a binding interaction kinetics in a number of emerging biological areas. This technique can be applied to the study of immune system diseases in order to contribute to improved understanding and evaluation of binding parameters for a variety of interactions between antigens and antibodies biochemically and clinically. Since the binding constants determination of an anti-protein dengue antibody (Ab) to a protein dengue antigen (Ag) is mostly complicated, the SPR technique aids a determination of binding parameters directly for a variety of particular dengue Ag_Ab interactions in the real-time. The study highlights the doctrine of real-time dengue Ag_Ab interaction kinetics as well as to determine the binding parameters that is performed with SPR technique. In addition, this article presents a precise prediction as a reference curve for determination of dengue sample concentration.

Issues in contemporary and potential future molecular diagnostics for dengue

INTRODUCTION

Dengue has been the most common arbovirus infection worldwide with 2.5 billion people living in over 100 endemic tropical and subtropical regions. Due to the high number of asymptomatic cases and the signs and symptoms being rather unspecific, dengue cases are often under-reported and might influence dengue surveillance programs. Therefore, a rapid, easy to use, inexpensive, and highly sensitive and specific diagnostic tool is essential for early and accurate diagnosis to ease the clinical management of patients as well as for the development of new interventions. Areas covered: This report discusses the contemporary dengue diagnostic tool, mainly from the aspect of molecular diagnosis where an overview of several nuclei acid amplification tests has been included. Potential molecular diagnostic tools such as biosensor and microarray are also discussed in this report. Expert commentary: Rapidness and accuracy in terms of sensitivity and specificity is imperative in dengue diagnosis for both clinical management and surveillance of dengue to ensure early treatment and corrective control measures can be carried out. In the next five years it is expected that there will be newer tests developed using not only the lateral flow techniques but more specifically biosensors and nanotechnology. These new technologies will have to be validated with the appropriate number and category of samples and to address the issue of cross-reactivity.

Validation and Application of a Commercial Quantitative Real-Time Reverse Transcriptase-PCR Assay in Investigation of a Large Dengue Virus Outbreak in Southern Taiwan

Background

Accurate, rapid, and early diagnosis of dengue virus (DENV) infections is essential for optimal clinical care. Here, we evaluated the efficacy of the quantitative real-time PCR (qRT-PCR)-LightMix dengue virus EC kit for DENV detection using samples from a dengue outbreak in Taiwan in 2015.

Methods

Sera from patients with suspected DENV infection were analyzed and compared using the LightMix kit, a Dengue NS1 Ag + Ab Combo kit for detection of NS1 antigen and DENV-specific IgM and IgG antibodies, and an “in-house” qualitative DENV-specific RT-PCR assay.

Results

A total of 8,989, 8,954, and 1581 samples were subjected to NS1 antigen detection, IgM and IgG detection, and LightMix assays, respectively. The LightMix assay yielded a linear curve for viral loads (VL) between 10² and 10⁶ copies/reaction, and the minimum detection limits for DENV serotype 1 (DENV1) and DENV2, DENV3, and DENV4 were 1, 10, and 100 focus forming units (FFU)/mL, respectively. There was 88.9% concordance between the results obtained using the NS1 antigen combo kit and by LightMix analysis, and the diagnostic sensitivity and specificity of the two methods were 89.4 and 100%, and 84.7 and 100%, respectively. Notably, fatal cases were attributed to DENV2 infection, and 79.5% (27/34) of these cases occurred in patients ≥ 71 years of age. Among these older patients, 82.3% (14/17) were NS1/IgM/IgG (+/-/-), exhibiting VLs between 10⁶–10⁹ copies/mL, which was markedly higher than the rate observed in the other age groups.

Conclusions

The LightMix assay was effective for early diagnosis of DENV infection. Our data indicate that high VLs during primary infection in elderly patients may be a positive predictor for severe illness, and may contribute to high mortality rates.

The LightMix dengue virus EC qRT-PCR assay is effective for early diagnosis of DENV infection. High viral loads during primary infection in elderly patients may comprise a positive predictor for severe illness, and may contribute to high mortality rates.

SERUM LEVELS OF COPPER AND IRON IN DENGUE FEVER

The role of trace elements in dengue virulence is not yet known. The present study assessed the serum levels of two micronutrients, copper and iron, in cases of dengue fever. The study involved 96 patients of whom 48 had either severe or non-severe forms of dengue (with and without warning signs), and the remaining 48 were patients with other febrile illnesses (OFI), used as controls. Serum levels of copper and iron were evaluated at admission and by the time of defervescence using commercially available kits. At admission, no difference in the level of serum copper was observed between cases and controls. In the group of dengue cases, the copper level was found to be significantly decreased in severe and non-severe cases with warning signs, compared to non-severe cases without warning signs. In contrast, by the time of defervescence the copper level was found to be increased in all dengue cases compared to OFI controls, but no difference was observed among dengue cases. Unlike OFI controls, dengue cases showed an increasing pattern of copper levels from admission until defervescence. On the other hand, no such significant differences were observed in the serum level of iron in the clinical groups, except for a decreased iron level found in severe cases, compared to non-severe dengue without warning signs. The results show that copper is associated with dengue severity and this finding emphasizes the need to investigate the involvement of trace elements in disease severity so as to improve the prognosis of dengue.

Is Reactive Dengue NS1Antigen Test a Warning Call for Hospital Admissions?

INTRODUCTION

Dengue fever is a major public health problem worldwide. The 2011 revised World Health Organization (WHO) guidelines have emphasized on early diagnosis and intervention to reduce the case fatality rate due to dengue fever. Rapid diagnostic tests like NS1 antigen assays have improved the detection of cases in early clinical phase of illness but its role as a predictor of severe dengue infection is not very clear.

AIM

To evaluate the utility of NS1 Ag assay as an early diagnostic marker and predictor of severe dengue infection.

MATERIALS AND METHODS

All children (0-12 years of age) diagnosed and confirmed with dengue fever at a tertiary care hospital in Puducherry between 01(st) August 2012 and 31(st) July 2015 were reviewed retrospectively from hospital case records as per the revised WHO guidelines for dengue fever. The diagnosis was confirmed by NS1antigen-based ELISA test or dengue serology for IgM and IgG antibodies and the data were analysed using SPSS 16.0 statistical software. After collecting all the data, all the variables were summarised by descriptive statistics. Categorical variables were expressed as frequencies and percentages, and then analysed by the χ(2) test or fishers exact test, where appropriate. Significance was taken at p-value< 0.05.

RESULTS

Among the 261 confirmed cases of dengue fever non-severe dengue and severe dengue infection was seen in 60.9% and 39.1% respectively. The mean age of presentation was 6.9 years and M:F ratio was 1.2:1. NS1 Ag was positive in 217 cases (83.1%) and among them non-severe dengue and severe dengue was seen in 65.9% and 34.1% cases respectively. A total of 44 cases (16.9%) were negative for NS1 Ag assay and positive for IgM MAC ELISA and among them 16 children (36.4%) had non-severe dengue infection where as 28 children (63.6%) had severe dengue infection. Secondary infection with (MAC-ELISA IgG) was seen in 17 cases (6.5%). NS1Ag assay was predominantly positive in acute phase sera, where as IgM/IgG MAC ELISA was predominantly positive in convalescent phase sera. There were six deaths (2.3%) and the common causes of poor outcome were multiorgan failure, encephalopathy and refractory shock.

CONCLUSION

NS1 Ag assay is a useful early diagnostic marker for dengue fever but cannot be used as an early predictor of severe dengue infection. The criteria for admission in hospitals of cases of dengue fever should be based on clinical warning signs rather than positive NS1 Antigen test.

Excretion of dengue virus RNA by Aedes aegypti allows non-destructive monitoring of viral dissemination in individual mosquitoes

Successful transmission of a vector-borne pathogen relies on a complex life cycle in the arthropod vector that requires initial infection of the digestive tract followed by systemic viral dissemination. The time interval between acquisition and subsequent transmission of the pathogen, called the extrinsic incubation period, is one of the most influential parameters of vector-borne pathogen transmission. However, the dynamic nature of this process is often ignored because vector competence assays are sacrificial and rely on end-point measurements. Here, we report that individual Aedes aegypti mosquitoes release large amounts of dengue virus (DENV) RNA in their excreta that can be non-sacrificially detected over time following oral virus exposure. Further, we demonstrate that detection of DENV RNA in excreta from individual mosquitoes is correlated to systemic viral dissemination with high specificity (0.9–1) albeit moderate sensitivity (0.64–0.89). Finally, we illustrate the potential of our finding to detect biological differences in the dynamics of DENV dissemination in a proof-of-concept experiment. Individual measurements of the time required for systemic viral dissemination, a prerequisite for transmission, will be valuable to monitor the dynamics of DENV vector competence, to carry out quantitative genetics studies, and to evaluate the risk of DENV transmission in field settings.

Increased number of cases of Chikungunya virus (CHIKV) infection imported from the Caribbean and Central America to northern Italy, 2014

This report describes an increased number of cases of Chikungunya virus (CHIKV) infection imported in northern Italy (Emilia-Romagna region) during the period May-September 2014, indicating that the recent spread of CHIKV and its establishment in the Caribbean and in central America, resulted in a high number of imported cases in Europe, thus representing a threat to public health. From May to September 2014, 14 imported cases of CHIKV infection were diagnosed; the patients were returning to Italy from Dominican Republic (n = 6), Haiti (n = 3), Guadeloupe (n = 2), Martinique (n = 1), Puerto Rico (n = 1) and Venezuela (n = 1). Phylogenetic analysis performed on the envelope protein (E1) gene sequences, obtained from plasma samples from two patients, indicated that the virus strain belongs to the Caribbean clade of the Asian genotype currently circulating in the Caribbean and Americas. The rise in the number of imported cases of CHIKV infection should increase healthcare professionals' awareness of the epidemiological situation and clinical presentation of CHIKV infection in order to enhance surveillance and early diagnosis in the forthcoming season of vector activity in Europe and North America.

Global emergence of Alphaviruses that cause arthritis in humans

Arthropod-borne viruses (arboviruses) may cause severe emerging and re-emerging infectious diseases, which pose a significant threat to human and animal health in the world today. These infectious diseases range from mild febrile illnesses, arthritis, and encephalitis to haemorrhagic fevers. It is postulated that certain environmental factors, vector competence, and host susceptibility have a major impact on the ecology of arboviral diseases. Presently, there is a great interest in the emergence of Alphaviruses because these viruses, including Chikungunya virus, O'nyong'nyong virus, Sindbis virus, Ross River virus, and Mayaro virus, have caused outbreaks in Africa, Asia, Australia, Europe, and America. Some of these viruses are more common in the tropics, whereas others are also found in temperate regions, but the actual factors driving Alphavirus emergence and re-emergence remain unresolved. Furthermore, little is known about the transmission dynamics, pathophysiology, genetic diversity, and evolution of circulating viral strains. In addition, the clinical presentation of Alphaviruses may be similar to other diseases such as dengue, malaria, and typhoid, hence leading to misdiagnosis. However, the typical presence of arthritis may distinguish between Alphaviruses and other differential diagnoses. The absence of validated diagnostic kits for Alphaviruses makes even routine surveillance less feasible. For that purpose, this review describes the occurrence, genetic diversity, clinical characteristics, and the mechanisms involving Alphaviruses causing arthritis in humans. This information may serve as a basis for better awareness and detection of Alphavirus-caused diseases during outbreaks and in establishing appropriate prevention and control measures.

Severe Dengue Fever Outbreak in Taiwan

Dengue fever (DF) is a vector-borne disease caused by dengue viruses (DENVs). Epidemic dengue occurs intermittently in Taiwan. In 2014, Taiwan experienced its largest DF outbreak. There were 15,732 DF cases reported. There were a total of 136 dengue hemorrhagic fever (DHF) cases, of which 20 resulted in death. Most DF cases were reported in southern Taiwan. A total of 15,043 (96%) cases were from Kaohsiung, a modern city in southern Taiwan. This report reviews DF epidemics in Taiwan during 2005-2014. The correlation between DF and DHF along with temperature and precipitation were conjointly examined. We conclude that most dengue epidemics in Taiwan resulted from imported DF cases. Results indicate three main factors that may have been associated with this DF outbreak in Kaohsiung: an underground pipeline explosion combined with subsequent rainfall and higher temperature. These factors may have enhanced mosquito breeding activity, facilitating DENV transmission.

Diagnosis of Dengue Infection Using Conventional and Biosensor Based Techniques

Dengue is an arthropod-borne viral disease caused by four antigenically different serotypes of dengue virus. This disease is considered as a major public health concern around the world. Currently, there is no licensed vaccine or antiviral drug available for the prevention and treatment of dengue disease. Moreover, clinical features of dengue are indistinguishable from other infectious diseases such as malaria, chikungunya, rickettsia and leptospira. Therefore, prompt and accurate laboratory diagnostic test is urgently required for disease confirmation and patient triage. The traditional diagnostic techniques for the dengue virus are viral detection in cell culture, serological testing, and RNA amplification using reverse transcriptase PCR. This paper discusses the conventional laboratory methods used for the diagnosis of dengue during the acute and convalescent phase and highlights the advantages and limitations of these routine laboratory tests. Subsequently, the biosensor based assays developed using various transducers for the detection of dengue are also reviewed.

Full-length infectious clone of a low passage dengue virus serotype 2 from Brazil

Full-length dengue virus (DENV) cDNA clones are an invaluable tool for many studies, including those on the development of attenuated or chimeric vaccines and on host-virus interactions. Furthermore, the importance of low passage DENV infectious clones should be highlighted, as these may harbour critical and unique strain-specific viral components from field-circulating isolates. The successful construction of a functional Brazilian low passage DENV serotype 2 full-length clone through homologous recombination reported here supports the use of a strategy that has been shown to be highly useful by our group for the development of flavivirus infectious clones and replicons.

Surveillance of adult Aedes mosquitoes in Selangor, Malaysia

OBJECTIVE

To determine the effectiveness of using sticky traps and the NS1 dengue antigen kit for the surveillance of Aedes mosquitoes for dengue control.

METHODS

Apartments were selected in a dengue-endemic area, and sticky traps were set to capture adult Aedes mosquitoes. NS1 dengue antigen kit was used to detect dengue antigen in mosquitoes, and positive mosquitoes were serotyped using real-time RT-PCR.

RESULTS

The sticky traps were effective in capturing Aedes aegypti, and a minimum of three traps per floor was sufficient. Multiple serotypes were found in individual mosquitoes.

CONCLUSION

The sticky trap and the NS1 dengue antigen test kit can be used as surveillance tool in dengue control programmes. This proactive method will be better suited for control programmes than current reactive methods.

Dengue patients exhibit higher levels of PrM and E antibodies than their asymptomatic counterparts

Dengue virus infection is a common tropical disease which often occurs without being detected. These asymptomatic cases provide information in relation to the manifestation of immunological aspects. In this study, we developed an ELISA method to compare neutralizing effects of dengue prM and E antibodies between dengue patients and their asymptomatic household members. Recombinant D2 premembrane (prM) was constructed, cloned, and tested for antigenicity. The recombinant protein was purified and tested with controls by using an indirect ELISA method. Positive dengue serum samples with their asymptomatic pair were then carried out onto the developed ELISA. In addition, commercially available recombinant envelope (E) protein was used to develop an ELISA which was tested with the same set of serum samples in the prM ELISA. Asymptomatic individuals showed preexisting heterotypic neutralizing antibodies. The recombinant prM was antigenically reactive in the developed ELISA. Dengue patients had higher prM and E antibodies compared to their household members. Our study highlights the neutralizing antibodies levels with respect to dengue prM and E between dengue patients and asymptomatic individuals.

Vector competence of the Aedes aegypti population from Santiago Island, Cape Verde, to different serotypes of dengue virus

Background

Dengue is an arboviral disease caused by dengue virus (DENV), whose main vectors are the mosquitoes Aedes aegypti and Aedes albopictus. A. aegypti is the only DENV vector in Cape Verde, an African country that suffered its first outbreak of dengue in 2009. However, little is known about the variation in the level of vector competence of this mosquito population to the different DENV serotypes. This study aimed to evaluate the vector competence of A. aegypti from the island of Santiago, Cape Verde, to four DENV serotypes and to detect DENV vertical transmission.

Methods

Mosquitoes were fed on blood containing DENV serotypes and were dissected at 7, 14 and 21 days post-infection (dpi) to detect the virus in the midgut, head and salivary glands (SG) using RT-PCR. Additionally, the number of copies of viral RNA present in the SG was determined by qRT-PCR. Furthermore, eggs were collected in the field and adult mosquitoes obtained were analyzed by RT-PCR and the platelia dengue NS1 antigen kit to detect transovarial transmission.

Results

High rates of SG infection were observed for DENV-2 and DENV-3 whereas for DENV-1, viral RNA was only detected in the midgut and head. DENV-4 did not spread to the head or SG, maintaining the infection only in the midgut. The number of viral RNA copies in the SG did not vary significantly between DENV-2 and DENV-3 or among the different periods of incubation and the various titers of DENV tested. With respect to DENV surveillance in mosquitoes obtained from the eggs collected in the field, no samples were positive.

Conclusion

Although no DENV positive samples were collected from the field in 2014, it is important to highlight that the A. aegypti population from Santiago Islands exhibited different degrees of susceptibility to DENV serotypes. This population showed a high vector competence for DENV-2 and DENV-3 strains and a low susceptibility to DENV-1 and DENV-4. Viral RNA copies in the SG remained constant for at least 21 dpi, which may enhance the vector capacity of A. aegypti and suggests the presence of a mechanism modulating virus replication in the SG.

Clinical diagnosis of early dengue infection by novel one-step multiplex real-time RT-PCR targeting NS1 gene

BACKGROUND

Dengue is a mosquito-borne disease that causes a public health problem in tropical and subtropical countries. Current immunological diagnostics based on IgM and/or nonstructural protein 1 (NS1) antigen are limited for acute dengue infection due to low sensitivity and accuracy.

OBJECTIVES

This study aimed to develop a one-step multiplex real-time RT-PCR assay showing higher sensitivity and accuracy than previous approaches.

STUDY DESIGN

Serotype-specific primers and probes were designed through the multiple alignment of NS1 gene. The linearity and limit of detection (LOD) of the assay were determined. The assay was clinically validated with an evaluation panel that was immunologically tested by WHO and Malaysian specimens.

RESULTS

The LOD of the assay was 3.0 log10 RNA copies for DENV-1, 2.0 for DENV-3, and 1.0 for DENV-2 and DENV-4. The assay showed 95.2% sensitivity (20/21) in an evaluation panel, whereas NS1 antigen- and anti-dengue IgM-based immunological assays exhibited 0% and 23.8-47.6% sensitivities, respectively. The assay showed 100% sensitivity both in NS1 antigen- and anti-dengue IgM-positive Malaysian specimens (26/26). The assay provided the information of viral loads and serotype with discrimination of heterotypic mixed infection.

CONCLUSIONS

The assay could be clinically applied to early dengue diagnosis, especially during the first 5 days of illness and approximately 14 days after infection showing an anti-dengue IgM-positive response.

Seropositivity of dengue antibodies during pregnancy

PURPOSE

Malaysia a dengue endemic country with dengue infections in pregnancy on the rise. The present study was aimed at determining dengue seroprevalence (IgG or IgM) during pregnancy and its neonatal transmission in dengue seropositive women.

METHODS

Maternal with paired cord blood samples were tested for dengue antibodies (IgG and IgM) using an enzyme-linked immunosorbent assay (ELISA). Maternal age, parity, occupation, ethnic group, and gestational age were recorded. Data on neonatal Apgar score and admissions to the Neonatal Intensive Care Unit (NICU) were analyzed.

RESULTS

Out of 358 women recruited, about 128 (35.8%) patients were seropositive. Twelve patients (3.4%) had recent infections (IgM positive) and another 116 women (32.4%) were with past infections (IgG positive). All babies born to seropositive mothers had positive IgG paired cord blood; however, no IgM seropositivity was observed. All neonates had good Apgar scores and did not require NICU admission.

CONCLUSION

In this study, 35.8% pregnant women were found to be dengue seropositive. However, transplacental transfer of IgG antibodies had no detrimental effect on the neonatal outcomes.

Universal single-probe RT-PCR assay for diagnosis of dengue virus infections

BACKGROUND

Dengue is a mosquito-borne viral disease that has become more prevalent in the last few decades. Most patients are viremic when they present with symptoms, and early diagnosis of dengue is important in preventing severe clinical complications associated with this disease and also represents a key factor in differential diagnosis. Here, we designed and validated a hydrolysis-probe-based one-step real-time RT-PCR assay that targets the genomes of dengue virus serotypes 1-4.

METHODOLOGY/PRINCIPAL FINDINGS

The primers and probe used in our RT-PCR assay were designed to target the 3' untranslated region of all complete genome sequences of dengue virus available in GenBank (n = 3,305). Performance of the assay was evaluated using in vitro transcribed RNA, laboratory-adapted virus strains, external control panels, and clinical specimens. The linear dynamic range was found to be 104-1011 GCE/mL, and the detection limit was between 6.0×102 and 1.1×103 GCE/mL depending on target sequence. The assay did not cross-react with human RNA, nor did it produce false-positive results for other human pathogenic flaviviruses or clinically important etiological agents of febrile illnesses. We used clinical serum samples obtained from returning travelers with dengue-compatible symptomatology (n = 163) to evaluate the diagnostic relevance of our assay, and laboratory diagnosis performed by the RT-PCR assay had 100% positive agreement with diagnosis performed by NS1 antigen detection. In a retrospective evaluation including 60 archived serum samples collected from confirmed dengue cases 1-9 days after disease onset, the RT-PCR assay detected viral RNA up to 9 days after appearance of symptoms.

CONCLUSIONS/SIGNIFICANCE

The validation of the RT-PCR assay presented here indicates that this technique can be a reliable diagnostic tool, and hence we suggest that it be introduced as the method of choice during the first 5 days of dengue symptoms.

Evaluation of commercially available diagnostic tests for the detection of dengue virus NS1 antigen and anti-dengue virus IgM antibody

Commercially available diagnostic test kits for detection of dengue virus (DENV) non-structural protein 1 (NS1) and anti-DENV IgM were evaluated for their sensitivity and specificity and other performance characteristics by a diagnostic laboratory network developed by World Health Organization (WHO), the UNICEF/UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (TDR) and the Pediatric Dengue Vaccine Initiative (PDVI). Each network laboratory contributed characterized serum specimens for the panels used in the evaluation. Microplate enzyme-linked immunosorbent assay (ELISA) and rapid diagnostic test (RDT formats) were represented by the kits. Each ELISA was evaluated by 2 laboratories and RDTs were evaluated by at least 3 laboratories. The reference tests for IgM anti-DENV were laboratory developed assays produced by the Armed Forces Research Institute for Medical Science (AFRIMS) and the Centers for Disease Control and Prevention (CDC), and the NS1 reference test was reverse transcriptase polymerase chain reaction (RT-PCR). Results were analyzed to determine sensitivity, specificity, inter-laboratory and inter-reader agreement, lot-to-lot variation and ease-of-use. NS1 ELISA sensitivity was 60–75% and specificity 71–80%; NS1 RDT sensitivity was 38–71% and specificity 76–80%; the IgM anti-DENV RDTs sensitivity was 30–96%, with a specificity of 86–92%, and IgM anti-DENV ELISA sensitivity was 96–98% and specificity 78–91%. NS1 tests were generally more sensitive in specimens from the acute phase of dengue and in primary DENV infection, whereas IgM anti-DENV tests were less sensitive in secondary DENV infections. The reproducibility of the NS1 RDTs ranged from 92-99% and the IgM anti-DENV RDTs from 88–94%.

Dengue virus (DENV) infection occurs throughout tropical and sub-tropical regions of the world where dengue is a major public health problem. Laboratory diagnosis of dengue with a single serum specimen obtained during the acute phase of the illness requires tests to detect IgM antibodies to DENV or the virus genome. A previous evaluation of available tests for IgM anti-DENV showed wide variability. The present study examined newly available commercial tests that detect the virus protein NS1, as well as new tests for IgM anti-DENV in microplate or rapid diagnostic test formats. This analytic study used specimens from laboratory confirmed dengue patients worldwide, which makes the results widely generalizable. The study found variability among the microplate ELISAs for both analytes but some tests performed with sensitivity and specificity acceptable for routine dengue diagnostics. The RDT's for both analytes had variable sensitivity that could be considered acceptable for routine clinical diagnostics. There is the need to maintain a network of dengue reference laboratories to conduct similar evaluations as additional dengue diagnostic tests become commercially available in order to guide the use for surveillance, clinical diagnosis and research.