Beneath the surface: Amino acid variation underlying two decades of dengue virus antigenic dynamics in Bangkok, Thailand.

Neutralizing antibodies are important correlates of protection against dengue. Yet, determinants of variation in neutralization across strains within the four dengue virus serotypes (DENV1-4) is imperfectly understood. Studies focus on structural DENV proteins, especially the envelope (E), the primary target of anti-DENV antibodies. Although changes in immune recognition (antigenicity) are often attributed to variation in epitope residues, viral processes influencing conformation and epitope accessibility also affect neutralizability, suggesting possible modulating roles of nonstructural proteins. We estimated effects of residue changes in all 10 DENV proteins on antigenic distances between 348 DENV collected from individuals living in Bangkok, Thailand (1994-2014). Antigenic distances were derived from response of each virus to a panel of twenty non-human primate antisera. Across 100 estimations, excluding 10% of virus pairs each time, 77 of 295 positions with residue variability in E consistently conferred antigenic effects; 52 were within ±3 sites of known binding sites of neutralizing human monoclonal antibodies, exceeding expectations from random assignments of effects to sites (p = 0.037). Effects were also identified for 16 sites on the stem/anchor of E which were only recently shown to become exposed under physiological conditions. For all proteins, except nonstructural protein 2A (NS2A), root-mean-squared-error (RMSE) in predicting distances between pairs held out in each estimation did not outperform sequences of equal length derived from all proteins or E, suggesting that antigenic signals present were likely through linkage with E. Adjusted for E, we identified 62/219 sites embedding the excess signals in NS2A. Concatenating these sites to E additionally explained 3.4% to 4.0% of observed variance in antigenic distances compared to E alone (50.5% to 50.8%); RMSE outperformed concatenating E with sites from any protein of the virus (ΔRMSE, 95%IQR: 0.01, 0.05). Our results support examining antigenic determinants beyond the DENV surface.

Reconstruction of antibody dynamics and infection histories to evaluate dengue risk.

As with many pathogens, most dengue infections are subclinical and therefore unobserved 1 . Coupled with limited understanding of the dynamic behaviour of potential serological markers of infection, this observational problem has wide-ranging implications, including hampering our understanding of individual- and population-level correlates of infection and disease risk and how these change over time, between assay interpretations and with cohort design. Here we develop a framework that simultaneously characterizes antibody dynamics and identifies subclinical infections via Bayesian augmentation from detailed cohort data (3,451 individuals with blood draws every 91 days, 143,548 haemagglutination inhibition assay titre measurements)2,3. We identify 1,149 infections (95% confidence interval, 1,135-1,163) that were not detected by active surveillance and estimate that 65% of infections are subclinical. After infection, individuals develop a stable set point antibody load after one year that places them within or outside a risk window. Individuals with pre-existing titres of ≤1:40 develop haemorrhagic fever 7.4 (95% confidence interval, 2.5-8.2) times more often than naive individuals compared to 0.0 times for individuals with titres >1:40 (95% confidence interval: 0.0-1.3). Plaque reduction neutralization test titres ≤1:100 were similarly associated with severe disease. Across the population, variability in the size of epidemics results in large-scale temporal changes in infection and disease risk that correlate poorly with age.

Precision Tracing of Household Dengue Spread Using Inter- and Intra-Host Viral Variation Data, Kamphaeng Phet, Thailand.

Dengue control approaches are best informed by granular spatial epidemiology of these viruses, yet reconstruction of inter- and intra-household transmissions is limited when analyzing case count, serologic, or genomic consensus sequence data. To determine viral spread on a finer spatial scale, we extended phylogenomic discrete trait analyses to reconstructions of house-to-house transmissions within a prospective cluster study in Kamphaeng Phet, Thailand. For additional resolution and transmission confirmation, we mapped dengue intra-host single nucleotide variants on the taxa of these time-scaled phylogenies. This approach confirmed 19 household transmissions and revealed that dengue disperses an average of 70 m per day between households in these communities. We describe an evolutionary biology framework for the resolution of dengue transmissions that cannot be differentiated based on epidemiologic and consensus genome data alone. This framework can be used as a public health tool to inform control approaches and enable precise tracing of dengue transmissions.

Dengue Virus (DENV) Neutralizing Antibody Kinetics in Children After Symptomatic Primary and Postprimary DENV Infection.

The immune response to dengue virus (DENV) infection is complex and not fully understood. Using longitudinal data from 181 children with dengue in Thailand who were followed for up to 3 years, we describe neutralizing antibody kinetics following symptomatic DENV infection. We observed that antibody titers varied by serotype, homotypic vs heterotypic responses, and primary versus postprimary infections. The rates of change in antibody titers over time varied between primary and postprimary responses. For primary infections, titers increased from convalescence to 6 months. By comparing homotypic and heterotypic antibody titers, we saw an increase in type specificity from convalescence to 6 months for primary DENV3 infections but not primary DENV1 infections. In postprimary cases, there was a decrease in titers from convalescence up until 6 months after infection. Beginning 1 year after both primary and postprimary infections, there was evidence of increasing antibody titers, with greater increases in children with lower titers, suggesting that antibody titers were boosted due to infection and that higher levels of neutralizing antibody may be more likely to confer a sterilizing immune response. These findings may help to model virus transmission dynamics and provide baseline data to support the development of vaccines and therapeutics.

Reconstruction of 60 Years of Chikungunya Epidemiology in the Philippines Demonstrates Episodic and Focal Transmission.

Proper understanding of the long-term epidemiology of chikungunya has been hampered by poor surveillance. Outbreak years are unpredictable and cases often misdiagnosed. Here we analyzed age-specific data from 2 serological studies (from 1973 and 2012) in Cebu, Philippines, to reconstruct both the annual probability of infection and population-level immunity over a 60-year period (1952-2012). We also explored whether seroconversions during 2012-2013 were spatially clustered. Our models identified 4 discrete outbreaks separated by an average delay of 17 years. On average, 23% (95% confidence interval [CI], 16%-37%) of the susceptible population was infected per outbreak, with >50% of the entire population remaining susceptible at any point. Participants who seroconverted during 2012-2013 were clustered at distances of <230 m, suggesting focal transmission. Large-scale outbreaks of chikungunya did not result in sustained multiyear transmission. Nevertheless, we estimate that >350 000 infections were missed by surveillance systems. Serological studies could supplement surveillance to provide important insights on pathogen circulation.

Genetic mapping of specific interactions between Aedes aegypti mosquitoes and dengue viruses.

Specific interactions between host genotypes and pathogen genotypes (G×G interactions) are commonly observed in invertebrate systems. Such specificity challenges our current understanding of invertebrate defenses against pathogens because it contrasts the limited discriminatory power of known invertebrate immune responses. Lack of a mechanistic explanation, however, has questioned the nature of host factors underlying G×G interactions. In this study, we aimed to determine whether G×G interactions observed between dengue viruses and their Aedes aegypti vectors in nature can be mapped to discrete loci in the mosquito genome and to document their genetic architecture. We developed an innovative genetic mapping strategy to survey G×G interactions using outbred mosquito families that were experimentally exposed to genetically distinct isolates of two dengue virus serotypes derived from human patients. Genetic loci associated with vector competence indices were detected in multiple regions of the mosquito genome. Importantly, correlation between genotype and phenotype was virus isolate-specific at several of these loci, indicating G×G interactions. The relatively high percentage of phenotypic variation explained by the markers associated with G×G interactions (ranging from 7.8% to 16.5%) is consistent with large-effect host genetic factors. Our data demonstrate that G×G interactions between dengue viruses and mosquito vectors can be assigned to physical regions of the mosquito genome, some of which have a large effect on the phenotype. This finding establishes the existence of tangible host genetic factors underlying specific interactions between invertebrates and their pathogens in a natural system. Fine mapping of the uncovered genetic loci will elucidate the molecular mechanisms of mosquito-virus specificity.

Multicountry prospective clinical evaluation of two enzyme-linked immunosorbent assays and two rapid diagnostic tests for diagnosing dengue fever.

We evaluated four dengue diagnostic devices from Alere, including the SD Bioline Dengue Duo (nonstructural [NS] 1 Ag and IgG/IgM), the Panbio Dengue Duo Cassette (IgM/IgG) rapid diagnostic tests (RDTs), and the Panbio dengue IgM and IgG capture enzyme-linked immunosorbent assays (ELISAs) in a prospective, controlled, multicenter study in Peru, Venezuela, Cambodia, and the United States, using samples from 1,021 febrile individuals. Archived, well-characterized samples from an additional 135 febrile individuals from Thailand were also used. Reference testing was performed on all samples using an algorithm involving virus isolation, in-house IgM and IgG capture ELISAs, and plaque reduction neutralization tests (PRNT) to determine the infection status of the individual. The primary endpoints were the clinical sensitivities and specificities of these devices. The SD Bioline Dengue Duo had an overall sensitivity of 87.3% (95% confidence interval [CI], 84.1 to 90.2%) and specificity of 86.8% (95% CI, 83.9 to 89.3%) during the first 14 days post-symptom onset (p.s.o.). The Panbio Dengue Duo Cassette demonstrated a sensitivity of 92.1% (87.8 to 95.2%) and specificity of 62.2% (54.5 to 69.5%) during days 4 to 14 p.s.o. The Panbio IgM capture ELISA had a sensitivity of 87.6% (82.7 to 91.4%) and specificity of 88.1% (82.2 to 92.6%) during days 4 to 14 p.s.o. Finally, the Panbio IgG capture ELISA had a sensitivity of 69.6% (62.1 to 76.4%) and a specificity of 88.4% (82.6 to 92.8%) during days 4 to 14 p.s.o. for identification of secondary dengue infections. This multicountry prospective study resulted in reliable real-world performance data that will facilitate data-driven laboratory test choices for managing patient care during dengue outbreaks.

Single dosage of doxycycline for prophylaxis against leptospiral infection and leptospirosis during urban flooding in southern Thailand: a non-randomized controlled trial.

This study was conducted to investigate the protective efficacy of a single dosage of 200 mg doxycycline against leptospiral infection and leptospirosis and associated risk factors among residents exposed to flooding in southern Thailand. Of 641 participants, 600 received doxycycline while 41 did not. Twenty two participants were infected with Leptospira and six developed leptospirosis. Having a laceration wound was significantly associated with leptospiral infection (odds ratio [OR] = 37.20; P < 0.001) and leptospirosis (OR = 18.24; P = 0.003) whereas exposure to flood more than 3 h per day was associated with only leptospiral infection (OR = 3.70; P = 0.038). Seventeen participants who received doxycycline and five who did not, were infected with Leptospira, resulting a protective efficacy of 76.8% (95% confidence interval [CI] = 34.3%-92.0%). Four who received doxycycline and two who did not, developed leptospirosis, resulting a protective efficacy of 86.3% (CI = -9.8%-98.2%). Among the participants with laceration wound, the protective efficacy for leptospiral infection was 92.0% (CI = 81.2%-96.6%) and for leptospirosis was 95.6% (CI = 78.2%-99.3%). Among the participants exposed to flood water less than or equal to 3 h per day, the protective efficacy for leptospiral infection was 89.2% (95% CI 63.6%-96.67%). A single dosage of 200 mg doxycycline for prophylaxis might be effective for preventing leptospirosis among flood victims with laceration wound after recent flood exposure.

Demographic, clinical and laboratory findings among adult and pediatric patients hospitalized with dengue in the Philippines.

We evaluated the differences in demographic, clinical, and laboratory findings between adult and pediatric patients hospitalized with dengue fever. Ninety patients with dengue infection admitted at San Lazaro Hospital (SLH), Manila from September 2005 to January 2006 were included in the study. The cases were laboratory-confirmed to have dengue infection. The majority of dengue cases (92%) had secondary dengue infection (median age = 18, age range: 2-37) while the remainder (8%) had a primary dengue infection (median age = 12, age range: 7-22). Nearly all the patients (99%) had dengue hemorrhagic fever (DHF). Sixty-five of the cases (72%) had serotype data: 2 (3%) were dengue virus serotype 1 (DENV-1) (median age = 17), 12 (18%) had DENV-2 (median age = 17.5), 38 (59%) had DENV-3 (median age = 16) and 13 (20%) had DENV-4 (median age = 18). The initial signs, symptoms and laboratory results except hematocrit (p = 0.02) and hemoglobin (p = 0.02) did not differ significantly between adults and children. During the study period, half the cases were adults (218 years; n = 45) and half were children (<18 years; n = 45). The ages of cases ranged from 2 to 37 years (median = 17 years) and the peak incidence was 15-19 years. Dengue is often considered as a pediatric disease. Additional studies are needed to determine if an age shift is occurring and where.

Antigenic distance between primary and secondary dengue infections correlates with disease risk.

Many pathogens continuously change their protein structure in response to immune-driven selection, resulting in weakened protection even in previously exposed individuals. In addition, for some pathogens, such as dengue virus, poorly targeted immunity is associated with increased risk of severe disease through a mechanism known as antibody-dependent enhancement. However, it remains unclear whether the antigenic distances between an individual's first infection and subsequent exposures dictate disease risk, explaining the observed large-scale differences in dengue hospitalizations across years. Here, we develop a framework that combines detailed antigenic and genetic characterization of viruses with details on hospitalized cases from 21 years of dengue surveillance in Bangkok, Thailand, to identify the role of the antigenic profile of circulating viruses in determining disease risk. We found that the risk of hospitalization depended on both the specific order of infecting serotypes and the antigenic distance between an individual's primary and secondary infections, with risk maximized at intermediate antigenic distances. These findings suggest that immune imprinting helps determine dengue disease risk and provide a pathway to monitor the changing risk profile of populations and to quantifying risk profiles of candidate vaccines.

Dengue-1 virus clade replacement in Thailand associated with enhanced mosquito transmission.

Dengue viruses (DENV) are characterized by extensive genetic diversity and can be organized in multiple, genetically distinct lineages that arise and die out on a regular basis in regions where dengue is endemic. A fundamental question for understanding DENV evolution is the relative extent to which stochastic processes (genetic drift) and natural selection acting on fitness differences among lineages contribute to lineage diversity and turnover. Here, we used a set of recently collected and archived low-passage DENV-1 isolates from Thailand to examine the role of mosquito vector-virus interactions in DENV evolution. By comparing the ability of 23 viruses isolated on different dates between 1985 and 2009 to be transmitted by a present-day Aedes aegypti population from Thailand, we found that a major clade replacement event in the mid-1990s was associated with virus isolates exhibiting increased titers in the vector's hemocoel, which is predicted to result in a higher probability of transmission. This finding is consistent with the hypothesis that selection for enhanced transmission by mosquitoes is a possible mechanism underlying major DENV clade replacement events. There was significant variation in transmission potential among isolates within each clade, indicating that in addition to vector-driven selection, other evolutionary forces act to maintain viral genetic diversity. We conclude that occasional adaptive processes involving the mosquito vector can drive major DENV lineage replacement events.

Hospital-based surveillance of Japanese encephalitis at a tertiary hospital in Manila.

Japanese encephalitis virus (JEV) is endemic in the Philippines but the incidence and burden of disease are not well established. We conducted a prospective hospital-based study at San Lazaro Hospital, a tertiary level hospital in Manila, from September 2005 to December 2006. Cases were determined using an in-house dengue and Japanese encephalitis (JE) enzyme-linked immunosorbent assay in order to detect the proportion of JE cases among the acute encephalitis syndrome (AES) cases admitted to our hospital. Fifteen patients were found to have AES, of whom 6 (40%) had confirmed JE. Of the JE cases, 4 were females and 2 were males with an age range of 3-14 years. Three of the 6 JE cases occurred during July. The most common signs and symptoms on admission among JE cases were: fever, headache, loss of appetite, neck rigidity and altered sensorium. JE likely comprises a significant proportion of hospitalized AES cases among children from Manila and nearby provinces. Further studies on the nation-wide prevalence and distribution of JE in the Philippines are needed to guide health authorities in disease control and prevention strategies.

Antigenic diversity and dengue disease risk.

Many pathogens continuously change their protein structure in response to immune-driven selection, resulting in weakened protection. In addition, for some pathogens such as dengue virus, poorly targeted immunity is associated with increased risk of severe disease, through a mechanism known as antibody-dependent enhancement. However, it remains a mystery whether the antigenic distance between an individual's first infection and subsequent exposures dictate disease risk, explaining the observed large-scale differences in dengue hospitalisations across years. Here we develop an inferential framework that combines detailed antigenic and genetic characterisation of viruses, and hospitalised cases from 21 years of surveillance in Bangkok, Thailand to identify the role of the antigenic profile of circulating viruses in determining disease risk. We find that the risk of hospitalisation depends on both the specific order of infecting serotypes and the antigenic distance between an individual's primary and secondary infections, with risk maximised at intermediate antigenic distances. These findings suggest immune imprinting helps determine dengue disease risk, and provides a pathway to monitor the changing risk profile of populations and to quantifying risk profiles of candidate vaccines.

Antibody persistence and immune memory response following primary vaccination and boosting with live attenuated SA 14-14-2 Japanese encephalitis vaccine (CD-JEV) in Bangladesh: A phase 4 open-label clinical trial.

INTRODUCTION: Japanese encephalitis (JE) virus is one of the leading causes of viral encephalitis across temperate and tropical zones of Asia. The live attenuated SA 14-14-2 JE vaccine (CD-JEV) is one of three vaccines prequalified by the World Health Organization (WHO) to prevent JE. WHO currently recommends a single CD-JEV dose for infants in endemic settings. However, in the absence of long-term immunogenicity data, WHO has indicated a need for long-term immunogenicity studies to inform optimal dosing schedules and determine the need for booster doses. METHODS: This Phase 4, open-label clinical study measured neutralizing antibody (NAb) titers in Bangladeshi children three and four years after primary CD-JEV vaccination and 7 and 28 days after a booster CD-JEV vaccination given four years after primary vaccination. The study also assessed the tolerability and safety of the booster dose. A NAb titer of ≥1:10 was considered seroprotective. RESULTS: Of 560 children vaccinated between 10 and 12 months of age with CD-JEV three years earlier and enrolled in this study from 30 July 2015 through 03 January 2016, 52 (9.3%; 95% CI: 7.2-12.0) had a seroprotective titer at enrollment. One year later, of 533 children, 66 (12.4%; 95% CI: 9.9-15.5) had a seroprotective titer before receiving a booster dose. Of 524 children who received a booster CD-JEV dose, 479 (91.4%; 95% CI: 88.7-93.5) and 514 (98.1%; 95% CI: 96.5-99.0) were seroprotected 7 and 28 days later, respectively. The geometric mean titer (GMT) was 6 (95% CI: 6-6) at baseline, 105 (95% CI: 93-119) 7 days post-booster, and 167 (95% CI: 152-183) 28 days post-booster. No vaccine-associated neurologic adverse events or other serious adverse events were noted following the booster dose. CONCLUSIONS: Although most children did not have measurable antibody titers three and four years after a single primary CD-JEV dose, more than 90% of seronegative children had a strong anamnestic response within one week of a booster dose. This suggests that these children were immune despite the absence of measurable NAb prior to their booster.ClinicalTrials.gov Identifier: NCT02514746.

A replication competent luciferase-secreting DENV2 reporter for sero-epidemiological surveillance of neutralizing and enhancing antibodies.

Dengue virus (DENV) specific neutralizing and enhancing antibodies play crucial roles in dengue disease prevention and pathogenesis. DENV reporters are gaining popularity in the evaluation of these antibodies; their accessibility and acceptance may improve with more efficient production systems and indications of their antigenic equivalence to the wild-type virus. This study aimed to generate a replication competent luciferase-secreting DENV reporter (LucDENV2) and evaluate its feasibility in neutralizing and infection-enhancing antibody assays in comparison with wild-type DENV2, strain 16681, and a luciferase-secreting, single-round infectious DENV2 reporter (LucSIP). LucDENV2 replicated to similarly high levels as that of the parent 16681 virus in a commonly used mosquito cell line. LucDENV2 was neutralized in an antibody concentration-dependent manner by a monoclonal antibody specific to the flavivirus fusion loop and two antibodies specific to the E domain III, which closely resembled the neutralization patterns employing the LucSIP and wild-type DENV2. Parallel analysis of LucDENV2 and wild-type DENV2 revealed good agreement between the luciferase-based and focus-based neutralization and enhancement assays in a 96-well microplate format when employed against a set of clinical sera, suggesting comparable antigenic properties of LucDENV2 with those of the parent virus. The high-titer, replication competent, luciferase-secreting DENV reporter presented here should be a useful tool for fast and reliable quantitation of neutralizing and infection-enhancing antibodies in populations living in DENV-endemic areas.

Dengue virus type 2 recognizes the carbohydrate moiety of neutral glycosphingolipids in mammalian and mosquito cells.

Dengue viruses infect cells by attaching to a surface receptor which remains unknown. The putative receptor molecules of dengue virus type 2 on the surface of mosquito (AP-61) and mammalian (LLC-MK2) cell lines were investigated. The immunochemical detection and structural analysis of carbohydrates demonstrated that the neutral glycosphingolipids, L-3 (GlcNAcß1-3Manß1-4Glcß1-1'Cer) in AP-61 cells, and nLc(4) Cer (Galß1-4GlcNAcß1-3Galß1-4Glcß1-1'Cer) in LLC-MK2 cells were recognized by the virus. These findings strongly suggest that neutral glycosphingolipids share the key determinant for virus binding and that the ß-GlcNAc residue may play an important role in dengue virus binding to the host cell surface.

Correlation between reported dengue illness history and seropositivity in rural Thailand.

In the latest World Health Organization (WHO) recommendation for Dengvaxia implementation, either serological testing or a person's history of prior dengue illness may be used as supporting evidence to identify dengue virus (DENV)-immune individuals eligible for vaccination, in areas with limited capacity for laboratory confirmation. This analysis aimed to estimate the concordance between self-reported dengue illness histories and seropositivity in a prospective cohort study for dengue virus infection in Kamphaeng Phet province, a dengue-endemic area in northern Thailand. The study enrolled 2,076 subjects from 516 multigenerational families, with a median age of 30.6 years (range 0-90 years). Individual and family member dengue illness histories were obtained by questionnaire. Seropositivity was defined based on hemagglutination inhibition (HAI) assays. Overall seropositivity for DENV was 86.5% among those aged 9-45 years, which increased with age. 18.5% of participants reported a history of dengue illness prior to enrollment; 30.1% reported a previous DENV infection in the family, and 40.1% reported DENV infection in either themselves or a family member. Relative to seropositivity by HAI in the vaccine candidate group, the sensitivity and specificity of individual prior dengue illness history were 18.5% and 81.6%, respectively; sensitivity and specificity of reported dengue illness in a family member were 29.8% and 68.0%, and of either the individual or a family member were 40.1% and 60.5%. Notably, 13.4% of individuals reporting prior dengue illness were seronegative. Given the high occurrence of asymptomatic and mild DENV infection, self-reported dengue illness history is poorly sensitive for prior exposure and may misclassify individuals as 'exposed' when they were not. This analysis highlights that a simple, highly sensitive, and highly specific test for determining serostatus prior to Dengvaxia vaccination is urgently needed.

Standardization and Evaluation of an Anti-ZIKV IgM ELISA Assay for the Serological Diagnosis of Zika Virus Infection.

Here, we describe the development of the in-house anti-Zika virus (ZIKV) IgM antibody capture ELISA (in-house ZIKV IgM ELISA) for the detection and diagnosis of acute ZIKV infections. We compared the in-house ZIKV IgM ELISA assay performance against two commercial kits, Euroimmun ZIKV IgM and InBios 2.0 ZIKV IgM ELISA. We tested the assays' ability to detect anti-ZIKV IgM using a well-defined serum sample panel. This panel included 80 ZIKV negative samples (20 negative, 20 found to be primary dengue virus [DENV][ infections, 20 secondary DENV infections, and 20 Japanese encephalitis virus [JEV] infections) and 67 ZIKV reverse transcriptase-polymerase chain reaction-positive acute serum samples. The OD values were calculated to enzyme immunoassay (EIA) unts by comparing them to weak positive controls. The results demonstrated the high sensitivity (88.06%) and specificity (90.00%) of our in-house ZIKV IgM ELISA and its 89.12% overall percentage agreement. The kappa values were deemed to be within excellent range and comparable to the InBios ZIKV IgM ELISA. Some cross-reactivity was observed among secondary DENV and JEV samples, and to a much lower extent, among primary DENV samples. These data indicate that our in-house ZIKV IgM ELISA is a reliable assay for the detection of anti-ZIKV IgM antibodies in serum.

Dengue pre-vaccination screening test evaluation for the use of dengue vaccine in an endemic area.

BACKGROUND: The dengue vaccine (Dengvaxia) is only recommended for individuals with prior dengue infection (PDI). This study aimed to perform a serosurvey to inform decision-making for vaccine introduction and identify appropriate target populations. We also evaluated the performance of the serological tests using plaque reduction neutralization test (PRNT) as a reference test in identifying PDI to determine suitability for pre-vaccination screening. METHODS: We enrolled 115 healthy individuals between 10 and 22 years of age living in the Ratchaburi province of Thailand. The serum samples were tested by PRNT to measure the prevalence and concentration of serotype-specific neutralizing antibodies. The performance of the IgG rapid diagnostic test (RDT, SD Bioline, Korea) and IgG enzyme-linked immunosorbent assay (ELISA, EUROIMMUN, Germany) in identifying PDI were evaluated by using PRNT as a reference method. RESULTS: Ninety-four (81.7%) individuals neutralized one or more dengue serotypes at a titer threshold greater than or equal to 10. Multitypic profiles were observed in 70.4% of the samples which increased to 91.9% in subjects aged 19-22. Among monotypic samples, the highest proportion was reactive against DENV-1 followed by DENV-2, DENV-3, and DENV-4. The highest anti-dengue antibody titers were recorded against DENV-1 and increased with age to a geometric mean NT50 titer (GMT) of 188.6 in the 19-22 age group. While both RDT and ELISA exhibited 100% specificity, RDT demonstrated low sensitivity (35%) with ELISA displaying much greater sensitivity (87%). CONCLUSIONS: Almost 80% of adolescents and youth in Ratchaburi province had already been exposed to one or more of the dengue virus serotypes. The dengue IgG RDT displayed low sensitivity and is likely not be suitable for dengue pre-vaccination screening. These results support the use of IgG ELISA test for dengue vaccination in endemic areas.