Dengue viremia kinetics in asymptomatic and symptomatic infection

Generating prophylactic immunity against arboviruses in vertebrates and invertebrates

The World Health Organization recently declared a global initiative to control arboviral diseases. These are mainly caused by pathogenic flaviviruses (such as dengue, yellow fever and Zika viruses) and alphaviruses (such as chikungunya and Venezuelan equine encephalitis viruses). Vaccines represent key interventions for these viruses, with licensed human and/or veterinary vaccines being available for several members of both genera. However, a hurdle for the licensing of new vaccines is the epidemic nature of many arboviruses, which presents logistical challenges for phase III efficacy trials. Furthermore, our ability to predict or measure the post-vaccination immune responses that are sufficient for subclinical outcomes post-infection is limited. Given that arboviruses are also subject to control by the immune system of their insect vectors, several approaches are now emerging that aim to augment antiviral immunity in mosquitoes, including Wolbachia infection, transgenic mosquitoes, insect-specific viruses and paratransgenesis. In this Review, we discuss recent advances, current challenges and future prospects in exploiting both vertebrate and invertebrate immune systems for the control of flaviviral and alphaviral diseases.

Dengue viremia kinetics and effects on platelet count and clinical outcomes: An analysis of 2340 patients from Vietnam

Background

Viremia is a critical factor in understanding the pathogenesis of dengue infection, but limited data exist on viremia kinetics. This study aimed to investigate the kinetics of viremia and its effects on subsequent platelet count, severe dengue, and plasma leakage.

Methods

We pooled data from three studies conducted in Vietnam between 2000 and 2016, involving 2340 dengue patients with daily viremia measurements and platelet counts after symptom onset. Viremia kinetics were assessed using a random effects model that accounted for left-censored data. The effects of viremia on subsequent platelet count and clinical outcomes were examined using a landmark approach with a random effects model and logistic regression model with generalized estimating equations, respectively. The rate of viremia decline was derived from the model of viremia kinetics. Its effect on the clinical outcomes was assessed by logistic regression models.

Results

Viremia levels rapidly decreased following symptom onset, with variations observed depending on the infecting serotype. DENV-1 exhibited the highest mean viremia levels during the first 5-6 days, while DENV-4 demonstrated the shortest clearance time. Higher viremia levels were associated with decreased subsequent platelet counts from day 6 onwards. Elevated viremia levels on each illness day increased the risk of developing severe dengue and plasma leakage. However, the effect size decreased with later illness days. A more rapid decline in viremia is associated with a reduced risk of the clinical outcomes.

Conclusions

This study provides comprehensive insights into viremia kinetics and its effect on subsequent platelet count and clinical outcomes in dengue patients. Our findings underscore the importance of measuring viremia levels during the early febrile phase for dengue studies and support the use of viremia kinetics as outcome for phase-2 dengue therapeutic trials.

Funding

Wellcome Trust and European Union Seventh Framework Programme.

Dengue virus transmission risk in blood donation: Evidence from Thailand

Individuals infected with dengue virus (DENV) often show no symptoms, which raises the risk of DENV transfusion transmission (TT-DENV) in areas where the virus is prevalent. This study aimed to determine the evidence of DENV infection in blood donors from different geographic regions of Thailand. A cross-sectional study was conducted on blood donor samples collected from the Thai Red Cross National Blood Center and four regional blood centers between March and September 2020. Screening for DENV nonstructural protein 1 (NS1), anti-DENV immunoglobulin G (IgG), and IgM antibodies was performed on residual blood from 1053 donors using enzyme-linked immunosorbent assay kits. Positive NS1 and IgM samples indicating acute infection were verified using four different techniques, including quantitative real-time (q) RT-PCR, nested PCR, virus isolation in C6/36 cells, and mosquito amplification. DENV IgG seropositivity was identified in 89% (938/1053) of blood donors. Additionally, 0.4% (4/1053) and 2.1% (22/1053) of Thai blood donors tested positive for NS1 and IgM, respectively. The presence of asymptomatic dengue virus infection in healthy blood donors suggests a potential risk of transmission through blood transfusion, posing a concern for blood safety.

Single-cell RNA sequencing reveals the expansion of circulating tissue-homing B cell subsets in secondary acute dengue viral infection

The roles of antibodies secreted by subsets of B cells in dengue virus (DENV) infection have been extensively studied, yet, the contribution of tissue-homing B cells to antiviral immunity remains unclear. In this study, we performed a comprehensive analysis of B cell subpopulations in peripheral blood samples from DENV-infected patients using single-cell RNA-sequencing (scRNA-seq) datasets and flow cytometry. We showed that plasma cells (PCs) and plasmablasts (PBs) were the predominant B cell populations during the acute phase of secondary natural DENV infection, but not in convalescent phase nor in healthy controls. Interestingly, these cells expressed proliferation, adhesion, and tissue-homing genes, including SELPLG, a homing marker of the skin, the initial infected site of DENV. Flow cytometry analysis confirmed a significant upregulation of cell surface expression of a cutaneous lymphocyte-associated antigen (CLA) encoded by SELPLG in PCs and PBs, compared to naive and memory B cells from the same patients. The analysis of an independent single-cell B-cell receptor sequencing (scBCR-seq) dataset of DENV-infected patients revealed that the peripheral blood PCs and PBs exhibited the highest clonal expansion in secondary DENV infection compared to other B cell subsets. These clonally expanded cells also expressed the highest levels of tissue-homing genes, including SELPLG. In addition, by utilizing a public scRNA-seq dataset of SARS-CoV2 infection, we demonstrated the upregulation of several tissue-homing genes in PCs and PBs. Our study provides evidence for the potential roles of tissue-homing B cell subsets in the context of immune responses against viral infections in humans.

Dengue: A review of laboratory diagnostics in the vaccine age

Background. Dengue is an important arboviral infection of considerable public health significance. It occurs in a wide global belt within a variety of tropical regions. The timely laboratory diagnosis of Dengue infection is critical to inform both clinical management and an appropriate public health response. Vaccination against Dengue virus is being introduced in some areas.Discussion. Appropriate diagnostic strategies will vary between laboratories depending on the available resources and skills. Diagnostic methods available include viral culture, the serological detection of Dengue-specific antibodies in using enzyme immunoassays (EIAs), microsphere immunoassays, haemagglutination inhibition or in lateral flow point of care tests. The results of antibody tests may be influenced by prior vaccination and exposure to other flaviviruses. The detection of non-structural protein 1 in serum (NS1) has improved the early diagnosis of Dengue and is available in point-of-care assays in addition to EIAs. Direct detection of viral RNA from blood by PCR is more sensitive than NS1 antigen detection but requires molecular skills and resources. An increasing variety of isothermal nucleic acid detection methods are in development. Timing of specimen collection and choice of test is critical to optimize diagnostic accuracy. Metagenomics and the direct detection by sequencing of viral RNA from blood offers the ability to rapidly type isolates for epidemiologic purposes.Conclusion. The impact of vaccination on immune response must be recognized as it will impact test interpretation and diagnostic algorithms.

Immunological signatures unveiled by integrative systems vaccinology characterization of dengue vaccination trials and natural infection

Introduction

Dengue virus infection is a global health problem lacking specific therapy, requiring an improved understanding of DENV immunity and vaccine responses. Considering the recent emerging of new dengue vaccines, here we performed an integrative systems vaccinology characterization of molecular signatures triggered by the natural DENV infection (NDI) and attenuated dengue virus infection models (DVTs).

Methods and results

We analyzed 955 samples of transcriptomic datasets of patients with NDI and attenuated dengue virus infection trials (DVT1, DVT2, and DVT3) using a systems vaccinology approach. Differential expression analysis identified 237 common differentially expressed genes (DEGs) between DVTs and NDI. Among them, 28 and 60 DEGs were up or downregulated by dengue vaccination during DVT2 and DVT3, respectively, with 20 DEGs intersecting across all three DVTs. Enriched biological processes of these genes included type I/II interferon signaling, cytokine regulation, apoptosis, and T-cell differentiation. Principal component analysis based on 20 common DEGs (overlapping between DVTs and our NDI validation dataset) distinguished dengue patients by disease severity, particularly in the late acute phase. Machine learning analysis ranked the ten most critical predictors of disease severity in NDI, crucial for the anti-viral immune response.

Conclusion

This work provides insights into the NDI and vaccine-induced overlapping immune response and suggests molecular markers (e.g., IFIT5, ISG15, and HERC5) for anti-dengue-specific therapies and effective vaccination development.

Flying under the radar - impact and factors influencing asymptomatic DENV infections

The clinical outcome of DENV and other Flaviviruses infections represents a spectrum of severity that ranges from mild manifestations to severe disease, which can ultimately lead to death. Nonetheless, most of these infections result in an asymptomatic outcome that may play an important role in the persistent circulation of these viruses. Also, although little is known about the mechanisms that lead to these asymptomatic infections, they are likely the result of a complex interplay between viral and host factors. Specific characteristics of the infecting viral strain, such as its replicating efficiency, coupled with host factors, like gene expression of key molecules involved in the immune response or in the protection against disease, are among crucial factors to study. This review revisits recent data on factors that may contribute to the asymptomatic outcome of the world's widespread DENV, highlighting the importance of silent infections in the transmission of this pathogen and the immune status of the host.

Seroprevalence of dengue virus infection in Pune City in India, 2019: A decadal change

BACKGROUND

The burden of dengue infection needs to be monitored along with tracking of the changes in dengue virus (DENV) transmission intensity for vaccine introduction decisions.

METHODS

The seroprevalence of dengue was investigated in Pune City in India, in early 2019 using 1654 sera from apparently healthy human participants enrolled randomly through multistage cluster sampling. We used 797 retrospective human sera from late 2009 for comparison. All sera were assessed for the presence of dengue-specific IgG antibodies. A subset (n = 230) was tested for serotype-specific plaque reduction-neutralizing antibodies against all four serotypes.

RESULTS

The dengue IgG seroprevalence of 62.9% (95% CI 59.4-66.1) in 2009 increased to 88.4% (95% CI 86.8-89.8) in 2019. Age-stratified dengue seroprevalence revealed a gradual increase in IgG seropositivity from 70.1% in 0-9 years to 85.0% in 10-19 years. The annual probability of dengue infection estimated as a force of infection was 4.1 (95% CI 3.8-4.5) in 2009, which increased to 10.9 (95% CI 10.2-11.6) in 2019. Analysis of dengue serotype-specific neutralizing antibodies revealed DENV-3 as the dominant serotype. The age of exposure to at least one dengue serotype was reduced in 2019 over 2009.

CONCLUSIONS

There was a significant increase in the intensity of dengue virus transmission in Pune City over the decade. Since over 85% of the participants above nine years of age had exposure to DENV by 2019, dengue vaccine introduction can be considered. Moreover, such repeated serosurveys in different regions might inform about the readiness of the population for dengue vaccination.

Influence of previous Zika virus infection on acute dengue episode

BACKGROUND

The co-circulation of flaviviruses in tropical regions has led to the hypothesis that immunity generated by a previous dengue infection could promote severe disease outcomes in subsequent infections by heterologous serotypes. This study investigated the influence of antibodies generated by previous Zika infection on the clinical outcomes of dengue infection.

METHODOLOGY/PRINCIPAL FINDINGS

We enrolled 1,043 laboratory confirmed dengue patients and investigated their prior infection to Zika or dengue. Severe forms of dengue disease were more frequent in patients with previous Zika infection, but not in those previously exposed to dengue.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that previous Zika infection may represent a risk factor for subsequent severe dengue disease, but we did not find evidence of antibody-dependent enhancement (higher viral titer or pro-inflammatory cytokine overexpression) contributing to exacerbation of the subsequent dengue infection.

Asymptomatic dengue infection rate: A systematic literature review

Objectives

Dengue infection is spreading worldwide. The clinical spectrum is broad and includes asymptomatic infections. This review provides an overview of the different proportions of asymptomatic infections described in epidemiological studies according to definitions, study designs, and detection methods.

Methods

Medline and Embase databases were searched without restriction of date or language. Studies were included if they reported data on the incidence or prevalence of asymptomatic dengue infections. The data were summarized and classified according to the definitions of the term 'asymptomatic'.

Results

A total of 74 studies were included. The mean proportion of asymptomatic infections among dengue-infected persons was 54% in 50 included studies. The prevalence of dengue infections detected in healthy persons was 0.2% in 24 included studies. The term 'asymptomatic' has been used to refer to 'clinically undetectable infection', but also to 'undiagnosed infection' or 'mild infection'. Only 8% were clinically undetectable laboratory-confirmed dengue infections.

Conclusion

The proportion of asymptomatic dengue infections varied greatly. Studies proving data on clinically undetectable laboratory-confirmed dengue infections were very few, but provided consistent results of low proportions of asymptomatic infections. These data challenge the assumption that the majority of dengue cases are asymptomatic.

Dengue: updates for dermatologists on the world's fastest-growing vector-borne disease

Dengue is the world's fastest-growing vector borne disease and has significant epidemic potential in suitable climates. Recent disease models incorporating climate change scenarios predict geographic expansion across the globe, including parts of the United States and Europe. It will be increasingly important in the next decade for dermatologists to become familiar with dengue, as it commonly manifests with rashes, which can be used to aid diagnosis. In this review, we discuss dengue for general dermatologists, specifically focusing on its cutaneous manifestations, epidemiology, diagnosis, treatment, and prevention. As dengue continues to spread in both endemic and new locations, dermatologists may have a larger role in the timely diagnosis and management of this disease.

A novel colorimetric biosensor for rapid detection of dengue virus upon acid-induced aggregation of colloidal gold

The dengue virus, once transmitted to people through a mosquito bite, causes an infectious disease called dengue fever. Dengue fever can develop into two fatal syndromes, namely dengue shock syndrome and dengue hemorrhagic fever. The existing strategies for detecting dengue infection mainly employ serological immunoassays and a real time PCR technique. Along with the positive features of efficiency, accuracy, and reproducibility, these procedures are limited by being time-consuming, costly, requiring special equipment for analysis, and unable to be carried out at the point-of-care level. Herein, we developed a colorimetric nanosensor for detecting dengue virus in clinical samples that is rapid, accurate, sensitive, and less expensive. The sensing platform relies on the specific binding between the DNA-conjugated AuNPs and genomic RNA of dengue, which results in the DNA-RNA heteroduplex structure formation that turns the gold colloid's ruby red color to blue due to the nano-aggregation in an acidic environment, which can be detected by the naked eye or measuring the absorbance. The DNA probe was designed to bind to a genomic RNA conserved region recognized in all four dengue serotypes. Dengue virus serotype 1 was utilized as a framework for virus detection; the designed nanosensor exhibited great specificity and selectivity, with the detection limit of ∼1 pg μL-1 (∼1.66 × 106 RNA copies per reaction) and time of analysis of about 1 h including the RNA extraction step. The proposed colorimetric nanosensor offers an alternative tool for specific and highly sensitive detection of dengue that eliminates the requirement for thermal cycling and primer sets in PCR-based assays.

Blockade-of-Binding Activities toward Envelope-Associated, Type-Specific Epitopes as a Correlative Marker for Dengue Virus-Neutralizing Antibody

Humans infected with dengue virus (DENV) acquire long-term protection against the infecting serotype, whereas cross-protection against other serotypes is short-lived. Long-term protection induced by low levels of type-specific neutralizing antibodies can be assessed using the virus-neutralizing antibody test. However, this test is laborious and time-consuming. In this study, a blockade-of-binding enzyme-linked immunoassay was developed to assess antibody activity by using a set of neutralizing anti-E monoclonal antibodies and blood samples from dengue virus-infected or -immunized macaques. Diluted blood samples were incubated with plate-bound dengue virus particles before the addition of an enzyme-conjugated antibody specific to the epitope of interest. Based on blocking reference curves constructed using autologous purified antibodies, sample blocking activity was determined as the relative concentration of unconjugated antibody that resulted in the same percent signal reduction. In separate DENV-1-, -2-, -3-, and -4-related sets of samples, moderate to strong correlations of the blocking activity with neutralizing antibody titers were found with the four type-specific antibodies 1F4, 3H5, 8A1, and 5H2, respectively. Significant correlations were observed for single samples taken 1 month after infection as well as samples drawn before and at various time points after infection/immunization. Similar testing using a cross-reactive EDE-1 antibody revealed a moderate correlation between the blocking activity and the neutralizing antibody titer only for the DENV-2-related set. The potential usefulness of the blockade-of-binding activity as a correlative marker of neutralizing antibodies against dengue viruses needs to be validated in humans. IMPORTANCE This study describes a blockade-of-binding assay for the determination of antibodies that recognize a selected set of serotype-specific or group-reactive epitopes in the envelope of dengue virus. By employing blood samples collected from dengue virus-infected or -immunized macaques, moderate to strong correlations of the epitope-blocking activities with the virus-neutralizing antibody titers were observed with serotype-specific blocking activities for each of the four dengue serotypes. This simple, rapid, and less laborious method should be useful for the evaluation of antibody responses to dengue virus infection and may serve as, or be a component of, an in vitro correlate of protection against dengue in the future.

Dengue incidence and length of viremia by RT-PCR in a prospective observational community contact cluster study from 2005-2009 in Indonesia

BACKGROUND

Dengue has become a major global health threat since being recognized three centuries ago. Important gaps remain in understanding the transmission dynamics of dengue virus (DENV) infection. This study reports the results of a prospective observational cluster study that investigated the incidence of symptomatic and asymptomatic infections and length of viremia among close community contacts of hospitalized DENV-infected patients.

METHODOLOGY/PRINCIPAL FINDINGS

Between 2005 and 2009, dengue-confirmed cases (n = 97) admitted to Hasan Sadikin Hospital in Bandung, Indonesia, were enrolled as index cases. Subsequently, twenty close community contacts (n = 1928) living with and around the index cases were included and followed up for up to 14 days. Body temperature was measured daily; blood samples were collected every 3-4 days and when reported fever. DENV infection was confirmed using Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR), IgM rapid test, and Enzyme-linked Immunosorbent Assay (ELISA). Among the 1928 community contacts, a total of 72 (3.7%) acute DENV infections were diagnosed, which equates to an incidence of 636 cases per 1,000 person-years (95% Confidence interval (CI) 588 to 687 cases per 1,000 person-years). Twenty-nine cases (40%) were symptomatic (22 dengue fever (DF) & 7 dengue hemorrhagic fever (DHF)), and 43 (60%) were asymptomatic. Primary and secondary DENV infections were detected in 18 (25%) and 54 (75%) subjects. Among the RT-PCR positives, viremia was observed as early as seven days before fever onset and converted to negative as late as seven days after the onset of fever.

CONCLUSIONS

DENV infections are common among close community contacts of hospitalized dengue patients. The high number of asymptomatic infections and the observation that viremia precedes the onset of fever for up to seven days highlight the importance of unrecognized dengue transmission and the need for improved transmission control.

Association of viral kinetics, infection history, NS1 protein with plasma leakage among Indonesian dengue infected patients

OBJECTIVES

Plasma leakage, a hallmark of disease in Dengue virus (DENV) infection, is an important clinical manifestation and is often associated with numerous factors such as viral factors. The aim of this study is to investigate the association of virus serotype, viral load kinetics, history of infection, and NS1 protein with plasma leakage.

METHODS

Subjects with fever ≤ 48 hours and positive DENV infection were included. Serial laboratory tests, viral load measurements, and ultrasonography examination to assess plasma leakage were performed.

RESULTS

DENV-3 was the most common serotype found in the plasma leakage group (35%). Patients with plasma leakage demonstrated a trend of higher viral load and a longer duration of viremia compared to those without. This was significantly observed on the fourth day of fever (p = 0.037). We found higher viral loads on specific days in patients with plasma leakage in both primary and secondary infections compared to those without. In addition, we also observed more rapid viral clearance in patients with secondary infection. NS1 protein, especially after 4 days of fever, was associated with higher peak viral load level, even though it was not statistically significant (p = 0.470). However, pairwise comparison demonstrated that peak viral load level in the group of patients with circulating NS1 detected for 7 days was significantly higher than the 5-day group (p = 0.037).

CONCLUSION

DENV-3 was the most common serotype to cause plasma leakage. Patients with plasma leakage showed a trend of higher viral load and a longer duration of viremia. Higher level of viral load was observed significantly on day 5 in patients with primary infection and more rapid viral clearance was observed in patients with secondary infection. Longer duration of circulating NS1 protein was also seen to be positively correlated with higher peak viral load level although not statistically significant.

Temporal patterns of functional anti-dengue antibodies in dengue infected individuals with different disease outcome or infection history

Heterotypic secondary dengue virus (DENV) infection is a risk factor for the development of severe disease. To assess the contribution of the developing polyclonal humoral immune response to the course of acute infection, we have determined anti-DENV IgG titers, neutralizing antibodies, percentages of antibodies binding to DENV-infected cells and antibody‑dependent enhancement (ADE) to the infecting serotype in DENV-infected Cambodian children (n = 58), ranging from asymptomatic dengue to severe disease. The results showed that ADE titers are highest against the infecting serotype during heterotypic secondary DENV-2 infection. Moreover, IgG titers, neutralizing antibodies and ADE titers against the infecting serotype peak at D10 and are maintained until D60 after laboratory-confirmed secondary DENV infection. Anti-DENV IgG titers and the magnitude of the functional antibody response were higher in secondary DENV-infected patients compared to primary infected patients. No differences in antibody titers, neutralizing or enhancing antibodies could be observed between asymptomatic or hospitalized patients between 6 and 8 days after laboratory-confirmed DENV-1 infection. However, at this time point, the level of IgG bound to DENV-infected cells was associated with disease severity in hospitalized patients. Taken together, our data offer insights for more comprehensive interpretation of antibody response profile to natural infection and its correlation to disease outcome.

A multiple-target mRNA-LNP vaccine induces protective immunity against experimental multi-serotype DENV in mice

Dengue virus (DENV) is a mosquito-borne virus with a rapid spread to humans, causing mild to potentially fatal illness in hundreds of millions of people each year. Due to the large number of serotypes of the virus, there remains an unmet need to develop protective vaccines for a broad spectrum of the virus. Here, we constructed a modified mRNA vaccine containing envelope domain III (E-DIII) and non-structural protein 1 (NS1) coated with lipid nanoparticles. This multi-target vaccine induced a robust antiviral immune response and increased neutralizing antibody titers that blocked all four types of DENV infection in vitro without significant antibody-dependent enhancement (ADE). In addition, there was more bias for Th1 than Th2 in the exact E-DIII and NS1-specific T cell responses after a single injection. Importantly, intramuscular immunization limited DENV transmission in vivo and eliminated vascular leakage. Our findings highlight that chimeric allogeneic structural and non-structural proteins can be effective targets for DENV vaccine and that they can prevent the further development of congenital DENV syndrome.

Monitoring human arboviral diseases through wastewater surveillance: Challenges, progress and future opportunities

Arboviral diseases are caused by a group of viruses spread by the bite of infected arthropods. Amongst these, dengue, Zika, west nile fever and yellow fever cause the greatest economic and social impact. Arboviral epidemics have increased in frequency, magnitude and geographical extent over the past decades and are expected to continue increasing with climate change and expanding urbanisation. Arboviral prevalence is largely underestimated, as most infections are asymptomatic, nevertheless existing surveillance systems are based on passive reporting of loosely defined clinical syndromes with infrequent laboratory confirmation. Wastewater-based surveillance (WBS), which has been demonstrated to be useful for monitoring diseases with significant asymptomatic populations including COVID19 and polio, could be a useful complement to arboviral surveillance. We review the current state of knowledge and identify key factors that affect the feasibility of monitoring arboviral diseases by WBS to include viral shedding loads by infected persons, the persistence of shed arboviruses and the efficiency of their recovery from sewage. We provide a simple model on the volume of wastewater that needs to be processed for detection of arboviruses, in face of lower arboviral shedding rates. In all, this review serves to reflect on the key challenges that need to be addressed and overcome for successful implementation of arboviral WBS.

Usage of FTA® Classic Cards for Safe Storage, Shipment, and Detection of Arboviruses

Infections caused by arthropod-borne RNA viruses are overrepresented among emerging infectious diseases. Effective methods for collecting, storing, and transporting clinical or biological specimens are needed worldwide for disease surveillance. However, many tropical regions where these diseases are endemic lack analytical facilities and possibility of continuous cold chains, which presents challenges from both a biosafety and material preservation perspective. Whatman^® FTA^® Classic Cards may serve as an effective and safe option for transporting hazardous samples at room temperature, particularly for RNA viruses classified as biosafety level (BSL) 2 and 3 pathogens, from sampling sites to laboratories. In this study, we investigated the biosafety and perseverance of representative alpha- and flaviviruses stored on FTA^® cards. To evaluate the virus inactivation capacity of FTA^® cards, we used Sindbis virus (SINV), chikungunya virus (CHIKV), and Japanese encephalitis virus (JEV). We inoculated susceptible cells with dilution series of eluates from viral samples stored on the FTA^® cards and observed for cytopathic effect to evaluate the ability of the cards to inactivate viruses. All tested viruses were inactivated after storage on FTA^® cards. In addition, we quantified viral RNA of JEV, SINV, and tick-borne encephalitis virus (TBEV) stored on FTA^® cards at 4 °C, 25 °C, and 37 °C for 30 days using two reverse transcriptase quantitative PCR assays. Viral RNA of SINV stored on FTA^® cards was not reduced at either 4 °C or 25 °C over a 30-day period, but degraded rapidly at 37 °C. For JEV and TBEV, degradation was observed at all temperatures, with the most rapid degradation occurring at 37 °C. Therefore, the use of FTA^® cards provides a safe and effective workflow for the collection, storage, and analysis of BSL 2- and 3-virus RNA samples, but there is a risk of false negative results if the cards are stored at higher temperatures for long periods of time. Conscious usage of the cards can be useful in disease surveillance and research, especially in tropical areas where transportation and cold chains are problematic.

Dengue Seroprevalence and Factors Associated with Dengue Seropositivity in Petaling District, Malaysia

Dengue virus (DENV) infection is a major public health concern, posing huge economic and disease burdens globally. In Malaysia, the incidence of DENV infections has increased significantly over the years. Nevertheless, the passive surveillance mechanism applied may not capture the actual magnitude of DENV infection. There was also a paucity of community-based studies exploring DENV seroprevalence. This study aimed to determine the DENV seroprevalence and the associated factors among the urban population in Petaling district, Malaysia. A population-based cross-sectional study was conducted from 18 August to 26 October 2018 with 533 participants recruited. Blood samples were collected and analysed for DENV seropositivity using a composite reference standard comprised of three dengue serological tests. Associated factors were identified by fitting Generalised Linear Mixed Models with binomial error structure and logit link function. DENV seroprevalence obtained was 79.0% (95% CI: 75.2–82.4%). The age-specific DENV seroprevalence showed an increasing trend with advancing age, from 22.7% (95% CI: 9.6–45.0%) for those aged below five years old to 94.9% (95% CI: 81.3–98.7%) for those aged ≥60 years old. Only age group and house level were found to be significant factors associated with DENV seropositivity. The odds of being DENV seropositive generally increased with age, from 13.43 (95% CI: 2.77–65.22) for the 5–9 years old age group to 384.77 (95% CI: 39.27–3769.97) for the ≥60 years old age group, as compared to those aged below 5 years old. For house level, those who lived on the first and second floor (OR: 8.98, 95% CI: 3.16–25.12) and the third floor and above (OR: 4.82, 95% CI: 1.89–12.32) had greater odds of being DENV seropositive compared to those living on the ground floor. This study demonstrated the persistently high DENV seroprevalence among the urban population in Petaling district, which could be useful to evaluate dengue control measures taken and estimate more accurate disease incidence. The associated factors with DENV seropositivity identified could also contribute to undertaking more targeted preventive and control measures.

Single-cell Temporal Analysis of Natural Dengue Infection Reveals Skin-Homing Lymphocyte Expansion One Day before Defervescence

Effective clinical management of acute dengue virus (DENV) infection relies on the timing of suitable treatments during the disease progression. We analyzed single-cell transcriptomic profiles of the peripheral blood mononuclear cell samples from two DENV patients, collected daily during acute phase and also at convalescence. Key immune cell types demonstrated different dynamic responses over the course of the infection. On the day before defervescence (Day −1), we observed the peak expression of several prominent genes in the adaptive immunological pathways. We also characterized unique effector T cell clusters that expressed skin-homing signature genes at Day −1, whereas upregulation of skin and gut homing genes was also observed in plasma cells and plasmablasts during the febrile period. This work provides an overview of unique molecular dynamics that signify the entry of the critical phase, and the findings could improve the patient management of DENV infection.

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Time-course scRNA-seq reveals immune response dynamics during acute dengue infection

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Rapid transcriptional switching was observed one day before fever subsided (Day -1)

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Skin-homing signatures were observed in specific T cells during the febrile phase

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Expansion of skin-homing CD69⁺ PD-1⁺ T cells at Day -1 was confirmed with FACS

Lack of Association between Adverse Pregnancy Outcomes and Zika Antibodies among Pregnant Women in Thailand between 1997 and 2015

Data about Zika virus infection and adverse pregnancy outcomes in Southeast Asia are scarce. We conducted an unmatched case-control study of Zika virus (ZIKV) serology in pregnant women enrolled in human immunodeficiency virus (HIV) or hepatitis B virus (HBV) perinatal prevention trials between 1997 and 2015 in Thailand. Case and control groups included women with and without adverse pregnancy outcomes. Plasma samples collected during the last trimester of pregnancy were tested for ZIKV IgG/IgM and Dengue IgG/IgM (Euroimmun, AG, Germany). Case newborn plasma samples were tested for ZIKV IgM and ZIKV RNA (Viasure, Spain). The case group included women with stillbirth (n = 22) or whose infants had microcephaly (n = 4), a head circumference below the first percentile (n = 14), neurological disorders (n = 36), or had died within 10 days after birth (n = 11). No women in the case group were positive for ZIKV IgM, and none of their live-born neonates were positive for ZIKV IgM or ZIKV RNA. The overall ZIKV IgG prevalence was 29%, 24% in the case and 34% in the control groups (Fisher's exact test; p = 0.13), while the dengue IgG seroprevalence was 90%. Neither neonatal ZIKV infections nor ZIKV-related adverse pregnancy outcomes were observed in these women with HIV and/or HBV during the 18-year study period.

Innate Lymphoid Cells Activation and Transcriptomic Changes in Response to Human Dengue Infection

Background

Dengue virus (DENV) infection has a global impact on public health. The clinical outcomes (of DENV) can vary from a flu-like illness called dengue fever (DF), to a more severe form, known as dengue hemorrhagic fever (DHF). The underlying innate immune mechanisms leading to protective or detrimental outcomes have not been fully elucidated. Helper innate lymphoid cells (hILCs), an innate lymphocyte recently discovered, functionally resemble T-helper cells and are important in inflammation and homeostasis. However, the role of hILCs in DENV infection had been unexplored.

Methods

We performed flow cytometry to investigate the frequency and phenotype of hILCs in peripheral blood mononuclear cells from DENV-infected patients of different disease severities (DF and DHF), and at different phases (febrile and convalescence) of infection. Intracellular cytokine staining of hILCs from DF and DHF were also evaluated by flow cytometry after ex vivo stimulation. Further, the hILCs were sorted and subjected to transcriptome analysis using RNA sequencing. Differential gene expression analysis was performed to compare the febrile and convalescent phase samples in DF and DHF. Selected differentially expressed genes were then validated by quantitative PCR.

Results

Phenotypic analysis showed marked activation of all three hILC subsets during the febrile phase as shown by higher CD69 expression when compared to paired convalescent samples, although the frequency of hILCs remained unchanged. Upon ex vivo stimulation, hILCs from febrile phase DHF produced significantly higher IFN-γ and IL-4 when compared to those of DF. Transcriptomic analysis showed unique hILCs gene expression in DF and DHF, suggesting that divergent functions of hILCs may be associated with different disease severities. Differential gene expression analysis indicated that hILCs function both in cytokine secretion and cytotoxicity during the febrile phase of DENV infection.

Conclusions

Helper ILCs are activated in the febrile phase of DENV infection and display unique transcriptomic changes as well as cytokine production that correlate with severity. Targeting hILCs during early innate response to DENV might help shape subsequent immune responses and potentially lessen the disease severity in the future.

Tree Shrew as a New Animal Model for the Study of Dengue Virus

Dengue virus is a significant public health threat worldwide; however, the pathogenesis of dengue disease remains poorly understood due to lack of appropriate small animal models. Tree shrews are an emerging experimental animal model for the study of human diseases due to their resemblance of genetic characteristics to primate animals. Herein we report that dengue infection in tree shrews elicits resemble clinical symptoms as in humans. Dengue fever (△2°C> normal body temperature) developed in ~22% healthy Chinese tree shrews from 2 through 33 days after infection with a low dose (1 ∗ 10⁴ PFU/animal) of dengue virus serotype 2 or 3 intravenously or subcutaneously. The dengue genomic RNA and neutralizing antibodies were detected in ~78% of animals at days 7 and 15 post infection respectively. The serum levels of liver enzymes including aspartate transaminase, alanine aminotransferase and alkaline phosphatase were elevated with peaks at day 7 after infection. Modest thrombocytopenia and a slight decrease in the white blood cell count were observed. Intriguingly, although viral RNA was barely detectable in the liver by 48 days after infection, it was still evident in the brain. The intra-brain bleeding lesions in the intravenous infection group were more severe than those in the subcutaneous infection group. Our data demonstrate that primary dengue virus infection in tree shrews causes resemble clinical disease as in humans and thus tree shrews may be a suitable model for the study of dengue disease pathogenesis.

Evaluation of the Models for Forecasting Dengue in Brazil from 2000 to 2017: An Ecological Time-Series Study

We aimed to evaluate the accuracy of deterministic and stochastic statistical models by means of a protocol developed in a free programming environment for monthly time-series analysis of the incidence of confirmed dengue cases in the states and federal district of Brazil from January 2000 to December 2017. This was an ecological time-series study conducted to evaluate and validate the accuracy of 10 statistical models for predicting the new cases of dengue. Official data on the monthly cases of dengue from January 2000 to December 2016 were used to train the statistical models, while those for the period January-December 2017 were used to test the predictive capacity of the models by considering three forecasting horizons (12, 6, and 3 months). Deterministic models proved to be reliable for predicting dengue in a 12-month forecasting horizon, while stochastic models were reliable for predicting the disease in a 3-month forecasting horizon. We were able to reliably employ models for predicting dengue in the states and federal district of Brazil. Hence, we strongly recommend incorporating these models in state health services for predicting dengue and for decision-making with regard to the advanced planning of interventions before the emergence of epidemics.