Human antibody response to dengue virus: implications for dengue vaccine design

Envelope-dimer epitope-like broadly protective antibodies against dengue in children following natural infection and vaccination

Cross-reactive antibodies (Abs) to epitopes that span envelope proteins on the virion surface are hypothesized to protect against dengue. Here, we measured Abs targeting the quaternary envelope dimer epitope (EDE) as well as neutralizing and binding Abs and evaluate their association with dengue virus (DENV) infection, vaccine response, and disease outcome in dengue vaccinated and unvaccinated children (n=252) within a longitudinal cohort in Cebu, Philippines (n=2,996). Abs targeting EDE were prevalent and strongly associated with broad neutralization of DENV1-4 in those with baseline multitypic immunity. Subsequent natural infection and vaccination boosted EDE-like, neutralizing, and binding Abs. EDE-like Abs were associated with reduced dengue risk and mediated the protective effect of binding and neutralizing Abs on symptomatic and severe dengue. Thus, Abs targeting quaternary epitopes help explain broad cross protection in those with multiple prior DENV exposures, making them useful for evaluation and development of future vaccines and therapeutics.

Factors associated with acute watery diarrhea among children aged 0-59 months in Obongi District, Uganda, April 2022: A case-control study

Background

Diarrheal diseases, are major concerns for Ugandan children; persistent in Obongi District despite high rotavirus vaccination rates (2019-2021). The district recorded the country's highest annual acute watery diarrhea (AWD) incidence from 2017 to 2021. Our study, conducted in April 2022, assessed AWD risk factors among 0-59-month-old children in Obongi.

Methods

We conducted a 1:2 (193:386) unmatched case-control study. A case was a child (0-59 months) with ≥ 3 loose/liquid stools/day, negative malaria/pneumonia tests, residing in Itula/Parolinya subcounty from 1 to 30 April 2022. Medical records from 10 facilities were reviewed. Simple random sampling identified cases, who were interviewed, and controls were randomly chosen from non-AWD neighboring households. Child health cards provided vaccination details. We used logistic regression to identify factors associated with AWD.

Results

Among 193 cases and 386 controls, 104 (54 %) cases and 183 (47 %) controls were male, 58 (30 %) cases and 127 (33 %) controls were aged 12-23 months, 187 (97 %) cases and 369 (96 %) controls had received at least one dose of rotavirus vaccine, 58 (30 %) cases and 120 (34 %) controls treated drinking water. Comorbidity presence (undernutrition, diabetes, HIV) (AOR = 12; CI: 2.5-53), caregiver's unwashed hands post-toilet (AOR = 3.9; CI: 1.2-13), and borehole vs. piped water (AOR = 4.0; CI: 1.7-9.6) linked to AWD.

Conclusion

Modifiable factors, including failure of caregivers to wash their hands with soap after visiting toilets and use of borehole water were associated with AWD, suggesting that community sensitization on handwashing at critical times, using clean water and soap, and expanded use of piped water could reduce AWD incidence in this area.

Qdenga® - A promising dengue fever vaccine; can it be recommended to non-immune travelers?

Qdenga® has been approved by the European Medicines Agency (EMA) for individuals > 4 years of age and for use according to national recommendations. The vaccine shows high efficacy against virologically confirmed dengue and severe dengue in clinical studies on 4-16-year old's living in endemic areas. For individuals 16-60 years old only serological data exists and there is no data for individuals > 60 years. Its use as a travel vaccine is still unclear. We present the studies behind the approval and the recommendations for travelers as issued by the Swedish Society for Infectious Diseases Physicians.

A randomized phase 3 trial of the immunogenicity and safety of coadministration of a live-attenuated tetravalent dengue vaccine (TAK-003) and an inactivated hepatitis a (HAV) virus vaccine in a dengue non-endemic country

BACKGROUND

Vaccination against hepatitis A virus (HAV) is largely recommended for travelers worldwide. Concurrent dengue and HAV vaccination may be desired in parallel for travelers to countries where both diseases are endemic. This randomized, observer-blind, phase 3 trial evaluated coadministration of HAV vaccine with tetravalent dengue vaccine (TAK-003) in healthy adults aged 18-60 years living in the UK.

METHODS

Participants were randomized (1:1:1) to receive HAV vaccine and placebo on Day 1, and placebo on Day 90 (Group 1), TAK-003 and placebo on Day 1, and TAK-003 on Day 90 (Group 2), or TAK-003 and HAV vaccine on Day 1, and TAK-003 on Day 90 (Group 3). The primary objective was non-inferiority of HAV seroprotection rate (anti-HAV ≥ 12.5 mIU/mL) in Group 3 versus Group 1, one month post-first vaccination (Day 30) in HAV-naïve and dengue-naïve participants. Sensitivity analyses were performed on combinations of baseline HAV and dengue serostatus. Secondary objectives included dengue seropositivity one month post-second vaccination (Day 120), HAV geometric mean concentrations (GMCs), and safety.

RESULTS

900 participants were randomized. On Day 30, HAV seroprotection rates were non-inferior following coadministration of HAV and TAK-003 (Group 3: 98.7 %) to HAV administration alone (Group 1: 97.1 %; difference: -1.68, 95 % CI: -8.91 to 4.28). Sensitivity analyses including participants who were neither HAV-naïve nor DENV-naïve at baseline supported this finding. Anti-HAV GMCs on Day 30 were 82.1 (95 % CI: 62.9-107.1) mIU/mL in Group 1 and 93.0 (76.1-113.6) mIU/mL in Group 3. By Day 120, 90.9-96.8 % of TAK-003 recipients were seropositive (neutralizing antibody titer > 10) to all four dengue serotypes. Coadministration of HAV vaccine and TAK-003 was well tolerated, with no important safety risks identified.

CONCLUSION

Immune responses following coadministration of HAV vaccine and TAK-003 were non-inferior to administration of HAV vaccine alone. The results support the coadministration of HAV vaccine and TAK-003 with no adverse impact on immunogenicity, safety, and reactogenicity of either vaccine.

CLINICALTRIALS

gov registration: NCT03525119.

Status of patient safety in selected Ghanaian hospitals: a national cross-sectional study

BACKGROUND

Safety is one of the dimensions of healthcare quality and is core to achieving universal health coverage and healthcare delivery worldwide. In Ghana, the status of patient safety in the last 7 years has remained unknown. Therefore, this study aims to assess the patient safety status in selected hospitals in Ghana.

METHODS

Using the WHO Patient Safety Long Form, a mixed methodology was used to assess the patient safety status in 27 hospitals in Ghana. Data were analysed using descriptive statistics and axial codes for thematic analysis.

RESULTS

The average national patient safety score was high (85%). However, there were variations in the performance of the hospitals across the WHO patient safety action areas. Knowledge and learning in patient safety (97%) was the highest-rated patient safety action area. Patient safety surveillance, patient safety funding, patient safety partnerships and national patient safety policy had mean scores lower than the national average score (85%). Less than half (42%) of the hospitals had a dedicated budget for patient safety activities. The means of continuous education for health professionals include clinical sessions, and in-service training, while the system of clinical audits in the hospitals were maternal mortality, perinatal mortality, stillbirth and general mortality audits. The hospitals use posters, leaflets, public address systems and health education sessions to inform patients about their rights. Patient safety issues are reported through suggestion boxes, designated desks and the use of contacts of core management staff.

CONCLUSION

The current patient safety status in the hospitals was generally good, with the highest score in the knowledge and learning in the patient safety domain. Patient safety surveillance was identified as the weakest action area. The findings of this study will form the scientific basis for initiating the development of a national patient safety policy in Ghana. This is crucial for ensuring resilient and sustainable health systems that guarantee safer care to all patients in Ghana.

Prevalence of intestinal parasites and associated factors among food handlers in food establishments in the Lideta subcity of Addis Ababa, Ethiopia: an institution-based, cross-sectional study

OBJECTIVE

This study was conducted to assess the prevalence of intestinal parasites and the associated factors among food handlers in the Lideta subcity of Addis Ababa, Ethiopia.

DESIGN

An institution-based, cross-sectional study design was used. Stool samples were collected from food handlers and examined using direct wet mount and formalin-ether concentration techniques. Personal and establishment-related information was collected using a pretested questionnaire, with a structured observation. Multivariable binary logistic regression was used to identify factors associated with the prevalence of intestinal parasites on the basis of adjusted OR (AOR) and 95% CI and p values <0.05.

SETTING

Food establishments in the Lideta subcity of Addis Ababa, Ethiopia.

PARTICIPANTS

411 food handlers participated in the study.

OUTCOME MEASURES

The primary outcome was the prevalence of intestinal parasites, defined as the presence of one or more intestinal parasitic species in stool samples.

RESULTS

One or more intestinal parasites were detected in 171 (41.6%; 95% CI 36.6% to 46.4%) stool samples. The most common intestinal parasites were Entamoeba histolytica/dispar (12.7%), Giardia duodenalis (11.2%) and Ascaris lumbricoides (8.3%). The presence of intestinal parasites among food handlers was associated with low monthly income (AOR: 2.83, 95% CI 1.50 to 8.84), untrimmed fingernails (AOR: 4.36, 95% CI 1.98 to 11.90), no food safety training (AOR: 2.51, 95% CI 1.20 to 5.58), low level of education (AOR: 3.13, 95% CI 1.34 to 7.44), poor handwashing practice (AOR: 2.16, 95% CI 1.03 to 4.22) and lack of medical check-up (AOR: 2.31, 95% CI 1.18 to 6.95).

CONCLUSION

The prevalence of intestinal parasites among food handlers in food establishments in the Lideta subcity of Addis Ababa was high. The presence of intestinal parasites was linked to socioeconomic conditions, poor hand hygiene conditions and absence of food safety training. It is crucially important to promote handwashing practices and provide food hygiene and safety training in these settings.

Implementation of the 5S-KAIZEN-TQM approach in a public hospital in Tunisia

INTRODUCTION

The 5S-Kaizen-TQM is a step-by-step approach, originally implemented in the Japanese industry as a continuous improvement strategy.

AIM

To underline the positive impact of its implementation in three pilot departments in Tunisia public hospital.

METHODS

The 5S-KAIZEN-TQM introduced into three clinical departments lasted 6 months from February 2021 to July 2021. Firstly, we organized seminar to introduce this approach and training sessions on 5S and Kaizen activities to each department staff members. To collect data, we conduct satisfaction surveys, face to face interviews, meetings, and brainstorming sessions. To present these data, checklists, Analytic Hierarchy Process (AHP), Ishikawa chart, Value stream mapping (VSM) charts and visual management techniques were adopted. Then, with the participation of the staff members, we implemented the two steps of this approach and evaluated their performance by the identification of indicators related to each step and to each Departement.

RESULTS

The project had positive implications on employee and patient satisfaction. 5S step activities leaded to the reduction of the item research time and the releases of space. Improving the working environment increased staff satisfaction. Kaizen activities conducted to the reduction of process lead time and the error reductions which increased patient satisfaction.

CONCLUSION

This project, first in Tunisia, was undertaken by Tunisian National Health Evaluation and Accreditation Agency (INEAS) and partners as part of the program for the research on organizational innovation in health. The fundings of this project can be disseminated and perpetuated the 5S-KAIZEN-TQM approach in the health sector in countrywide.

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.

Prevalence of and factors associated with childhood diarrhoeal disease and acute respiratory infection in Bangladesh: an analysis of a nationwide cross-sectional survey

OBJECTIVES

This study aimed to estimate the prevalence of childhood diarrhoeal diseases (CDDs) and acute respiratory infections (ARIs) and also to determine the factors associated with these conditions at the population level in Bangladesh.

SETTING

The study entailed an analysis of nationally representative cross-sectional secondary data from the most recent Bangladesh Demographic and Health Survey conducted in 2017-2018.

PARTICIPANTS

A total of 7222 children aged below 5 years for CDDs and 7215 children aged below 5 years for ARIs during the survey from mothers aged between 15 and 49 years were the participants of this study. In the bivariate and multivariable analyses, we used Pearson χ2 test and binary logistic regression, respectively, for both outcomes.

RESULTS

The overall prevalence of CDD and ARI among children aged below 5 years was found to be 4.91% and 3.03%, respectively. Younger children were more likely to develop both CDDs and ARIs compared with their older counterparts. Children belonging to households classified as poorest and with unimproved floor materials had a higher prevalence of diarrhoea than those from households identified as richest and with improved floor material, respectively. Stunted children had 40.8% higher odds of diarrhoea than normal children. Being male and having mothers aged below 20 years were 48.9% and two times more likely to develop ARI than female counterparts and children of mothers aged 20-34 years, respectively. Children whose mothers had no formal education or had primary and secondary education had higher odds of ARI compared with children of mothers having higher education.

CONCLUSION

This study found that children aged below 24 months were at higher risk of having CDDs and ARIs. Thus, programmes targeting these groups should be designed and emphasis should be given to those from poorest wealth quintile to reduce CDDs and ARIs.

Discovery of B-cell epitopes for development of dengue vaccines and antibody therapeutics

Dengue is one of the most frequently transmitted viral infections globally which creates a serious burden to the healthcare system in many countries in the tropical and subtropical regions. To date, no vaccine has demonstrated balanced protection against the four dengue serotypes. Dengvaxia as the only vaccine that has been licensed for use in endemic areas has shown an increased risk in dengue-naïve vaccines to develop severe dengue. A crucial element in protection from dengue infection is the neutralizing antibody responses. Therefore, the identification of protective linear B-cell epitopes can guide vaccine design and facilitate the development of monoclonal antibodies as dengue therapeutics. This review summarizes the identification of dengue B-cell epitopes within the envelope (E) protein of dengue that can be incorporated into peptide vaccine constructs. These epitopes have been identified through approaches such as bioinformatics, three-dimensional structure analysis of antibody-dengue complexes, mutagenesis/alanine scanning and escape mutant studies. Additionally, the therapeutic potential of monoclonal antibodies targeting the E protein of dengue is reviewed. This can provide a basis for the design of future dengue therapies.

Natural immunogenic properties of bioinformatically predicted linear B-cell epitopes of dengue envelope and pre-membrane proteins

Background

The natural antibody responses to B-cell epitopes from dengue structural proteins were assessed using immune sera from people having well-defined past dengue infections with one of the four serotypes.

Method

Based on an immune-computational analysis previously conducted, nineteen epitopes from the envelope (E) and eight epitopes from pre-membrane (prM), which were more than 50% conserved across all the four DENV serotypes, were selected. Peptides to represent these B-cell epitopes were obtained from commercially available arrays, and were subjected to enzyme linked immunosorbent assay with sera obtained from dengue seropositive healthy volunteers (DENV1 n = 12: DENV2 n = 12: DENV3 n = 12 and DENV4 n = 12), and 10 dengue seronegative healthy volunteers from Sri Lanka. The cut-off value for the positive antibody response was set by taking the mean response of a peptide to the negative sera plus three standard deviations. The peptides (N = 7) showing the broad immune responses were used to generate antibodies in three mice (Balb/c) batches. The mice antisera were then subjected to microneutralization assays against all the four DENV serotypes. An EC₅₀ viral neutralization ≥ 40 times the serum dilution was considered as neutralizing.

Results

Five of the E-peptide and two prM peptides were recognised by most individuls exposed to infections with each of the four serotypes, showing a serotype cross-reactive broad antibody response. The mice immune sera against the peptides representing the five E protein epitopes neutralized all the four DENV serotypes. Two of these five epitopes are from the Domain II, whereas one of them includes the whole bc-loop region.

Conclusion

The antibody responses of highly conserved epitopes across the serotypes, were broadly responsive with sera of all four DENV serotypes collected from individuals infected with only one DENV serotype. Weakly conserved epitopes showed rather specific antibody responses dominated by one or few serotypes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12865-021-00462-4.

Evaluation of the extended efficacy of the Dengvaxia vaccine against symptomatic and subclinical dengue infection

More than half of the world's population lives in areas at risk for dengue virus infection. A vaccine will be pivotal to controlling spread, however, the only licensed vaccine, Dengvaxia, has been shown to increase the risk of severe disease in a subset of individuals. Vaccine efforts are hampered by a poor understanding of antibody responses, including those generated by vaccines, and whether antibody titers can be used as a marker of protection from infection or disease. Here we present the results of an ancillary study to a phase III vaccine study (n = 611). All participants received three doses of either Dengvaxia or placebo and were followed for 6 years. We performed neutralization tests on annual samples and during confirmed dengue episodes (n = 16,508 total measurements). We use mathematical models to reconstruct long-term antibody responses to vaccination and natural infection, and to identify subclinical infections. There were 87 symptomatic infections reported, and we estimated that there were a further 351 subclinical infections. Cumulative vaccine efficacy was positive for both subclinical and symptomatic infection, although the protective effect of the vaccine was concentrated in the first 3 years following vaccination. Among individuals with the same antibody titer, we found no difference between the risk of subsequent infection or disease between placebo and vaccine recipients, suggesting that antibody titers are a good predictor of both protection and disease risk.

Exploring the socio-economic determinants of educational inequalities in diarrhoea among under-five children in low- and middle-income countries: a Fairlie decomposition analysis

BACKGROUND

What explains the underlying causes of educational inequalities in diarrhoea among under-five children in low- and middle-income countries (LMIC) is poorly exploited, operationalized, studied and understood. This paper aims to assess the magnitude of educational-related inequalities in the development of diarrhoea and decompose risk factors that contribute to these inequalities among under-five children (U5C) in LMIC.

METHODS

Secondary data of 796,150 U5C from 63,378 neighbourhoods in 57 LMIC was pooled from the Demographic and Health Surveys (DHS) conducted between 2010 and 2019. The main determinate variable in this decomposition study was mothers' literacy levels. Descriptive and inferential statistics comprising of bivariable analysis and binary logistic multivariable Fairlie decomposition techniques were employed at p = 0.05.

RESULTS

Of the 57 countries, we found a statistically significant pro-illiterate odds ratio in 6 countries, 14 showed pro-literate inequality while the remaining 37 countries had no statistically significant educational-related inequality. The countries with pro-illiterate inequalities are Burundi (OR = 1.11; 95% CI: 1.01-1.21), Cameroon (OR = 1.84; 95% CI: 1.66-2.05), Egypt (OR = 1.26; 95% CI: 1.12-1.43), Ghana (OR = 1.24; 95% CI: 1.06-1.47), Nigeria (OR = 1.80; 95% CI: 1.68-1.93), and Togo (OR = 1.21; 95% CI: 1.06-1.38). Although there are variations in factors that contribute to pro-illiterate inequality across the 6 countries, the overall largest contributors to the inequality are household wealth status, maternal age, neighbourhood SES, birth order, toilet type, birth interval and place of residence. The widest pro-illiterate risk difference (RD) was in Cameroon (118.44/1000) while the pro-literate risk difference was widest in Albania (- 61.90/1000).

CONCLUSIONS

The study identified educational inequalities in the prevalence of diarrhoea in children with wide variations in magnitude and contributions of the risk factors to pro-illiterate inequalities. This suggests that diarrhoea prevention strategies is a must in the pro-illiterate inequality countries and should be extended to educated mothers as well, especially in the pro-educated countries. There is a need for further studies to examine the contributions of structural and compositional factors associated with pro-educated inequalities in the prevalence of diarrhoea among U5C in LMIC.

Evaluating the Safety of West Nile Virus Immunity During Congenital Zika Virus Infection in Mice

Antibody-dependent enhancement (ADE) is a phenomenon that occurs when cross-reactive antibodies generated from a previous flaviviral infection increase the pathogenesis of a related virus. Zika virus (ZIKV) is the most recent flavivirus introduced to the Western Hemisphere and has become a significant public health threat due to the unanticipated impact on the developing fetus. West Nile virus (WNV) is the primary flavivirus that circulates in North America, and we and others have shown that antibodies against WNV are cross-reactive to ZIKV. Thus, there is concern that WNV immunity could increase the risk of severe ZIKV infection, particularly during pregnancy. In this study, we examined the extent to which WNV antibodies could impact ZIKV pathogenesis in a murine pregnancy model. To test this, we passively transferred WNV antibodies into pregnant Stat2^-/- mice on E6.5 prior to infection with ZIKV. Evaluation of pregnant dams showed weight loss following ZIKV infection; however, no differences in maternal weights or viral loads in the maternal brain, spleen, or spinal cord were observed in the presence of WNV antibodies. Resorption rates, and other fetal parameters, including fetal and placental size, were similarly unaffected. Further, the presence of WNV antibodies did not significantly alter the viral load or the inflammatory response in the placenta or the fetus in response to ZIKV. Our data suggest that pre-existing WNV immunity may not significantly impact the pathogenesis of ZIKV infection during pregnancy. Our findings are promising for the safety of implementing WNV vaccines in the continental US.

Sero-epidemiological study on Dengue fever virus in humans and camels at Upper Egypt

BACKGROUND AND AIM

Dengue fever (DF) is an important mosquito-borne viral zoonosis affecting over 100 countries worldwide and putting about 3.9 billion people at risk of infection. The disease has re-emerged in Egypt since 2011; however, there is a paucity of recent epidemiological data available. Therefore, in this study, we employed a cross-sectional study to determine DF prevalence in humans and camels in Asyut and Sohag Governorates, Egypt, during 2019.

MATERIALS AND METHODS

A total of 91 humans and a similar number of dromedary camels were utilized in this study. Sera were obtained and analyzed for the presence of specific antibodies against DF virus using enzyme-linked immunosorbent assay. Related epidemiological data affecting the disease spread in humans and camels were recorded and statistically analyzed.

RESULTS

The seroprevalence of DF in humans and camels was 12.09% and 3.3%, respectively. The disease varied significantly by the species examined as humans were found to be at a higher risk of acquiring the infection compared to camels. Nearly equal odds of exposure (odds ratio [OR]) were seen in the individuals with close contact with camels compared to those without; however, individuals exposed to mosquitoes were at approximately 3 times higher risk of infection (OR=2.95 [95% confidence interval [CI], 0.73-11.93]) compared to individuals who were not exposed to mosquitoes (OR=0.033 [95% CI, 0.084-1.37]). Interestingly, DF seropositivity in camels was significantly related to the presence or absence of symptoms within 2 weeks before sampling (p=0.02) where symptomatic animals had higher odds of exposure (OR=19.51 [95%, 0.97-392.3]) compared to asymptomatic ones (OR=0.05 [95%, 0.002-1.03]).

CONCLUSION

The current study reports the presence of specific antibodies against dengue virus (DENV) in humans residing within Asyut and Sohag Governorates, Egypt. Furthermore, it provides the first serological evidence of DENV circulation in camels which is alarming. A more comprehensive study is needed; however, this baseline investigation underscores the urgent need for increasing awareness among people residing in the area as well as application of the appropriate mosquito control measures to avoid further spread of the disease.

Phenotype and functionality of follicular helper T cells in patients with acute dengue infection

Background

The association of functionality and phenotype of follicular helper T cells (Tfh) with dengue virus (DENV) specific antibody responses and clinical disease severity has not been well studied.

Methods

We investigated the phenotype and functionality of Tfh cells and plasmablasts in adult patients (DF = 18, DHF = 22) with acute dengue (day 4 to 8 since onset of fever) of varying severity using multiparametric flowcytometry. The properties of Tfh cells were correlated with viraemia, disease severity, plasmablast responses and DENV-specific serum antibody responses. We further evaluated the kinetics of neutralizing antibodies (Neut50) throughout the course of illness in order to evaluate their association with clinical disease severity and viraemia.

Results

Tfh cells (especially those producing IL-21 and co-expressing PD-1 and ICOS) were found to be significantly expanded (p < 0.0001) and highly activated in patients with DHF compared to those with DF. The frequency of Tfh cells significantly correlated with DENV-specific IgG, NS1-specific antibodies and Neut50 antibody titres in patients with DHF but not in those with DF. Although the Neut50 titres increased during the course of acute secondary DENV infection, they showed differences based on serotype. For instance, the Neut50 titres were significantly higher during the latter part of illness in patients with DF compared to DHF in DENV1 infection, while in DENV2, patients with DHF had significantly higher titres. The viral loads during early illness did not correlate with the subsequent rise in the Neut50 antibody titres during any time point of illness.

Conclusions

The expansion of Tfh cells is associated with DHF and DENV-specific IgG, NS1-specific and neutralizing antibodies. Neut50 titres did not associate with disease severity or viraemia at the point of first presentation during the febrile phase, but later titres do show differential association with severity in patients with DENV1 compared to DENV2.

Non-Human Primate Models of Dengue Virus Infection: A Comparison of Viremia Levels and Antibody Responses during Primary and Secondary Infection among Old World and New World Monkeys

Due to the global burden of dengue disease, a vaccine is urgently needed. One of the key points in vaccine development is the development of a robust and reliable animal model of dengue virus infection. Characteristics including the ability to sustain viral replication, demonstration of clinical signs, and immune response that resemble those of human dengue virus infection are vital in animal models. Preclinical studies in vaccine development usually include parameters such as safety evaluation, induction of viremia and antigenemia, immunogenicity, and vaccine effectiveness. Although mice have been used as a model, non-human primates have an advantage over mice because of their relative similarity to humans in their genetic composition and immune responses. This review compares the viremia kinetics and antibody responses of cynomolgus macaques (Macaca fasicularis), common marmosets (Callithrix jacchus), and tamarins (Saguinus midas and Saguinus labitus) and summarize the perspectives and the usefulness along with challenges in dengue vaccine development.

Concurrent Methicillin-Resistant Staphylococcus aureus Septicemia and Thyroid Abscess in a Young Male with Dengue

BACKGROUND

Dengue fever is an arthropod-borne viral infection with a very high incidence rate in Southeast Asia. Most patients present with self-limiting febrile illness, while some patients may develop complications like acute kidney injury, acute liver failure, myocarditis or Guillain- Barre syndrome. The coexistence of Dengue and MRSA (Methicillin-resistant Staphylococcus aureus ) is rarely reported in the literature.

CASE

A 28-year-old male is presented with high-grade fever, polyserositis and thrombocytopenia. The patient was treated symptomatically for dengue infection. During the course of hospitalization, patient developed neck swelling (thyroid abscess) and left forearm abscess. MRSA was isolated from blood culture and pus, and successfully treated with iv antibiotics (Vancomycin).

CONCLUSION

High anticipation and vigilance are required to detect concurrent bacteremia in dengue patients. Early recognition of warning signs with readily antibiotic therapy is important to prevent mortality and morbidity in these patients. Our report also highlights the MRSA as a rare cause of thyroid abscess, with only 5 cases reported in the literature so far.

Annexin II as a Dengue Virus Serotype 2 Interacting Protein Mediating Virus Interaction on Vero Cells

Recent evidence has demonstrated that dengue virus requires active filopodia formation for a successful infection. However, the cellular factor involved in the interaction has not been fully elucidated. We used a combination of virus overlay protein binding assay and LC-MS/MS, and identified annexin II as a dengue virus serotype 2 (DENV2) interacting protein on Vero cells, upon filopodia induction. Flow cytometry analysis showed annexin II on the Vero cells surface increased when DENV2 was added. The amount of annexin II in the plasma membrane fraction was reduced as the infection progressed. Antibody-mediated inhibition of infection and siRNA-mediated knockdown of annexin II expression significantly reduced DENV2 infection and production levels. Collectively, we demonstrated that annexin II is one of the host factor involved in DENV2 binding on Vero cells.

Dengue and Chikungunya Infections in Children : Guest Editor: Bhim S. Pandhi

Dengue and Chikungunya are two important mosquito-borne acute febrile illnesses in children. With increased urbanization and newer strains of chikungunya virus with improved transmission with Aedes albopictus, the at-risk population for these infections has greatly increased. Dengue fever has been classified by WHO as dengue with/ without warning signs and severe dengue. Severe dengue is associated with hemorrhagic manifestations, hypovolemia and hypotension secondary to third space loss due to capillary leak or severe end organ dysfunction. NS1 antigen detection and dengue polymerase chain reaction, [polymerase chain reaction (PCR during first 5 d)] and IgM for dengue (6th day of fever onwards) are commonly utilized diagnostic tests. Appropriate fluid therapy with timely tapering of intravenous fluid rate with hematocrit, treatment of hemorrhagic manifestations and clinical monitoring are the mainstay of dengue treatment. Chikungunya has less severe course with shorter febrile phase with prominent and persistent joint symptoms. PCR and IgM against chikungunya are appropriate investigations. Treatment is supportive for chikungunya infection with appropriate joint pain relief.

Circulation of dengue serotypes in the Union Territory of Dadra & Nagar Haveli (India)

The presence of chronological infection by the multi serotype of dengue virus (DENV) is a major contributing factor for the induction of Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS). The results indicate that all serotype of dengue along with concurrent infection were reported from the third smallest Union Territory of India furthermore, rare serotype DENV 4, gradually spreads in new areas of India. Therefore, a need to understand the epidemiology of locally circulating serotype and accordingly the control strategy can be implemented. The study was conducted during 2014-2017 in the Union Territory of Dadra & Nagar Haveli (India).

Dengue in Singapore from 2004 to 2016: Cyclical Epidemic Patterns Dominated by Serotypes 1 and 2

Singapore has experienced periodic dengue epidemics despite maintaining a low Aedes house index. Each epidemic was associated with a switch in the predominant serotype. We investigated the temporal dynamics of dengue fever and dengue virus (DENV) and analyzed the epidemiological and entomological patterns of dengue in Singapore from 2004 to 2016. The case surveillance is based on a mandatory notification system that requires all medical practitioners to report clinically suspected and laboratory-confirmed cases. Circulating (DENV) serotypes are monitored through a virus surveillance program. Entomological surveillance involves inspections for larval breeding and monitoring of adults using gravitraps. Singapore experienced a similar epidemic pattern during 2004–2007 and 2013–2016. The pattern involved a 2-year DENV-1 epidemic occurring after a switch in the predominant serotype from DENV-2 to DENV-1, followed by a “lull” year. Thereafter, the predominant serotype switched back to DENV-2, tailed by a small-scale epidemic. Across the years, the highest incidence group was in the 25–44 years age group. The incidence rate of those aged ≥ 55 years was about half of that of the 15–24 years age group during DENV-1 predominant years. However, it was almost equal to the younger age group in DENV-2 predominant years. Types of Aedes aegypti breeding habitats remained similar. Dengue incidence was significantly higher in areas with high breeding percentage (BP) than areas with low BP (P < 0.05). In conclusion, the oscillation of DENV-1 and DENV-2, throughout the 13-year period, led to a cyclical epidemic pattern and older adults were more affected by DENV-2 than DENV-1.

Genotype-specific and cross-reactive neutralizing antibodies induced by dengue virus infection: detection of antibodies with different levels of neutralizing activities against homologous and heterologous genotypes of dengue virus type 2 in common marmosets (Callithrix jacchus)

BACKGROUND

A vaccine against all four dengue virus (DENV) serotypes includes the formulation of one genotype of each serotype. Although genetic similarities among genotypes within a serotype are higher as compared to those among serotypes, differences in the immunogenicity of the included genotypes would be a critical issue in maximizing successful dengue vaccine development. Thus, we determined the neutralizing antibody responses against three genotypes of dengue virus serotype 2 (DENV-2), namely Cosmopolitan, Asian I, and Asian/American, after primary and secondary inoculation with DENV-2 in a dengue animal model, the common marmoset (Callithrix jacchus).

METHODS

A total of fifty-four plasma samples were obtained from thirty-four marmosets that were inoculated with clinically-isolated DENV strains or DENV candidate vaccines, were used in this study. Plasma samples were obtained from marmosets after primary inoculation with DENV-2 infection, secondary inoculation with homologous or heterologous genotypes, and tertiary inoculation with heterologous DENV. Neutralizing antibody titers against DENV-2 (Cosmopolitan, Asian I, and Asian/American genotypes) and DENV-1 were determined using a conventional plaque reduction neutralization assay.

RESULTS

In marmosets that were inoculated with the Cosmopolitan genotype in primary infection, neutralizing antibody neutralized 3 genotypes, and the titers to Asian I genotype were significantly higher than those to homologous Cosmopolitan genotype. After secondary DENV-2 infection with heterologous genotype (Asian I in primary and Asian/American in secondary), neutralizing antibody titers to Asian/American genotype was significantly higher than those against Cosmopolitan and Asian I genotypes. Following tertiary infection with DENV-1 following DENV-2 Asian I and Cosmopolitan genotypes, neutralizing antibody titers to Asian/American were also significantly higher than those against Cosmopolitan and Asian I genotypes.

CONCLUSION

The present study demonstrated that different levels of neutralizing antibodies were induced against variable DENV-2 genotypes after primary, secondary and tertiary infections, and that neutralizing antibody titers to some heterologous genotypes were higher than those to homologous genotypes within a serotype. The results indicate that heterogeneity and homogeneity of infecting genotypes influence the levels and cross-reactivity of neutralizing antibodies induced in following infections. The results also suggest that certain genotypes may possess advantage in terms of breakthrough infections against vaccination.

Development of Peptide Vaccines in Dengue

Dengue is one of the most important arboviral infections worldwide, infecting up to 390 million people and causing 25,000 deaths annually. Although a licensed dengue vaccine is available, it is not efficacious against dengue serotypes that infect people living in South East Asia, where dengue is an endemic disease. Hence, there is an urgent need to develop an efficient dengue vaccine for this region. Data from different clinical trials indicate that a successful dengue vaccine must elicit both neutralizing antibodies and cell mediated immunity. This can be achieved by designing a multi-epitope peptide vaccine comprising B, CD8+ and CD4+ T cell epitopes. As recognition of T cell epitopes are restricted by human leukocyte antigens (HLA), T cell epitopes which are able to recognize several major HLAs will be preferentially included in the vaccine design. While peptide vaccines are safe, biocompatible and cost-effective, it is poorly immunogenic. Strategies to improve its immunogenicity by the use of long peptides, adjuvants and nanoparticle delivery mechanisms are discussed.

RIG-I-like receptor activation by dengue virus drives follicular T helper cell formation and antibody production

Follicular T helper cells (TFH) are fundamental in orchestrating effective antibody-mediated responses critical for immunity against viral infections and effective vaccines. However, it is unclear how virus infection leads to TFH induction. We here show that dengue virus (DENV) infection of human dendritic cells (DCs) drives TFH formation via crosstalk of RIG-I-like receptor (RLR) RIG-I and MDA5 with type I Interferon (IFN) signaling. DENV infection leads to RLR-dependent IKKε activation, which phosphorylates IFNα/β receptor-induced STAT1 to drive IL-27 production via the transcriptional complex ISGF3. Inhibiting RLR activation as well as neutralizing antibodies against IL-27 prevented TFH formation. DENV-induced CXCR5+PD-1+Bcl-6+ TFH cells secreted IL-21 and activated B cells to produce IgM and IgG. Notably, RLR activation by synthetic ligands also induced IL-27 secretion and TFH polarization. These results identify an innate mechanism by which antibodies develop during viral disease and identify RLR ligands as potent adjuvants for TFH-promoting vaccination strategies.

Humanized mouse models to study human cell-mediated and humoral responses to dengue virus

Several candidate dengue virus vaccines are in clinical trials and show promise as an effective measure to control dengue. However, it is becoming clear that additional vaccine candidates may be needed as there is concern about the durability of the immune response to all four serotypes of vaccine components and efficacy varies dependent on the immune status of the individual. The lack of an appropriate animal model to mimic human dengue has deterred the development of vaccines and anti-viral therapies to dengue virus. The focus of this review is to discuss advances in the development of humanized animal models and to highlight how they could be used for antiviral and dengue vaccine testing if limitations with cell-mediated immunity and seroconversion to IgG are overcome.

Clinical Efficacy, Safety, and Immunogenicity of a Live Attenuated Tetravalent Dengue Vaccine (CYD-TDV) in Children: A Systematic Review with Meta-analysis

BACKGROUND

Dengue hemorrhagic fever is the leading cause of hospitalization and death in children living in Asia and Latin America. There is an urgent need for an effective and safe dengue vaccine to reduce morbidity and mortality in this high-risk population given the lack of dengue specific treatment at present. This review aims to determine the efficacy, safety, and immunogenicity of CYD-TDV vaccine in children.

METHODS

This is a systematic review including meta-analysis of randomized controlled clinical trial data from Embase, Medline, the Cochrane Library, Web of Science, and ClinicalTrials.gov. Studies that assessed CYD-TDV vaccine efficacy [(1 - RR)*100], safety (RR), and immunogenicity (weighted mean difference) in children were included in this study. Random effects model was employed to analyze patient-level data extracted from primary studies.

RESULTS

The overall efficacy of CYD-TDV vaccine was 54% (40-64), while serotype-specific efficacy was 77% (66-85) for DENV4, 75% (65-82) for DENV3, 50% (36-61) for DENV1, and 34% (14-49) for DENV2. 15% (-174-74) vaccine efficacy was obtained for the unknown serotype. Meta-analysis of included studies with longer follow-up time (25 months) revealed that CYD-TDV vaccine significantly increased the risk of injection site reactions (RR = 1.1: 1.04-1.17; p-value = 0.001). Immunogenicity (expressed as geometric mean titers) in descending order was 439.7 (331.7-547.7), 323 (247 - 398.7), 144.1 (117.9-170.2), and 105 (88.7-122.8) for DENV3, DENV2, DENV1, and DENV4, respectively.

CONCLUSION

CYD-TDV vaccine is effective and immunogenic in children overall. Reduced efficacy of CYD-TDV vaccine against DENV2 notoriously known for causing severe dengue infection and dengue outbreaks cause for serious concern. Post hoc meta-analysis of long-term follow-up data (≥25 months) from children previously vaccinated with CYD-TDV vaccine is needed to make a conclusion regarding CYD-TDV vaccine safety in children. However, CYD-TDV vaccine should be considered for use in regions where DENV2 is not endemic as currently there is no specific treatment for dengue infection.

Occurrence of concurrent infections with multiple serotypes of dengue viruses during 2013-2015 in northern Kerala, India

BACKGROUND

Dengue is a global human public health threat, causing severe morbidity and mortality. The occurrence of sequential infection by more than one serotype of dengue virus (DENV) is a major contributing factor for the induction of Dengue Hemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS), two major medical conditions caused by DENV infection. However, there is no specific drug or vaccine available against dengue infection. There are reports indicating the increased incidence of concurrent infection of dengue in several tropical and subtropical regions. Recently, increasing number of DHF and DSS cases were reported in India indicating potential enhancement of concurrent DENV infections. Therefore, accurate determination of the occurrence of DENV serotype co-infections needs to be conducted in various DENV prone parts of India. In this context, the present study was conducted to analyse the magnitude of concurrent infection in northern Kerala, a southwest state of India, during three consecutive years from 2013 to 2015.

METHODS

A total of 120 serum samples were collected from the suspected dengue patients. The serum samples were diagnosed for the presence of dengue NS1 antigen followed by the isolation of dengue genome from NS1 positive samples. The isolated dengue genome was further subjected to RTPCR based molecular serotyping. The phylogenetic tree was constructed based on the sequence of PCR amplified products.

RESULTS

Out of the total number of samples collected, 100 samples were positive for dengue specific antigen (NS1) and 26 of them contained the dengue genome. The RTPCR based molecular serotyping of the dengue genome revealed the presence of all four serotypes with different combinations. However, serotypes 1 and 3 were predominant combinations of concurrent infection. Interestingly, there were two samples with all four serotypes concurrently infected in 2013.

DISCUSSION

All samples containing dengue genome showed the presence of more than one serotype, indicating 100% concurrent infection. However, the combination of serotypes 1 and 3 was predominant. To the best of our knowledge, this is the first report indicating the concurrent infection of dengue in the northern Kerala, India. The phylogenetic analysis of dengue serotype 1 identified in this study shows a close relationship with the strain isolated in Delhi and South Korea during the 2006 and 2015 epidemics respectively. Similarly this study indicates that the phylogeny of dengue serotype 3 of northern Kerala is more closely related to dengue isolate of Rajasthan state, India. The geographical and climatic conditions of Kerala favours the breeding of both the mosquito vectors of dengue (Aedes albopictus and Aedes aegypti), which may enhance the severity of dengue in the future. Therefore, the study provides an alarming message for the urgent need of an antiviral strategy or other health management systems to curb the spread of dengue infection.