RESUMEN
Background: Dengue is the most prevalent mosquito-borne viral disease and a major public health problem worldwide. Most primary infections with the four dengue virus serotypes (DENV1-4) are inapparent; nevertheless, prior research has primarily focused on symptomatic infections, which has limited our understanding of the epidemiological burden and spectrum of disease of each DENV serotype. Our study addresses this bottleneck in dengue research by providing a new method and a detailed examination of primary inapparent infections. Methods: Here we present (1) the evaluation of a multiplex DENV1-4 envelope domain III multiplex microsphere-based assay (EDIII-MMBA) to serotype inapparent primary infections and (2) its application leveraging 17 years of prospective sample collection from the Nicaraguan Pediatric Dengue Cohort Study. After evaluation, we analyzed 46% (N=574) of total inapparent primary DENV infections with the EDIII-MMBA. Remaining infections were inferred using stochastic imputation, taking year and neighborhood of infection into account. Findings: The EDIII-MMBA demonstrated excellent diagnostic accuracy of symptomatic and inapparent primary DENV infections when evaluated against gold-standard serotyping methods. Significant within- and between-year variation in serotype distribution between symptomatic and inapparent infections and circulation of serotypes undetected in symptomatic cases were observed in multiple years. Our findings reveal that a significant majority of primary infections remained inapparent: 76.8% for DENV1, 79.9% for DENV2, and 63.9% for DENV3. DENV3 exhibited the highest likelihood of symptomatic and severe primary infections (Pooled OR compared to DENV1 = 2.13, 95% CI 1.28-3.56, and 6.75, 2.01-22.62, respectively), whereas DENV2 had similar likelihood to DENV1 in both analyses. Interpretation: Our study indicates that case surveillance skews the perceived epidemiological footprint of DENV and reveals a more complex and intricate pattern of serotype distribution in inapparent infections. Further, the significant differences in infection outcomes by serotype emphasizes the need for serotype-informed public health strategies. Funding: NIH/NIAID P01AI106695, U01AI153416. Research in context: Evidence before this study: We conducted a search in PubMed for studies published up to February 2024. Keywords included "dengue virus" and "DENV" in combination with "inapparent infections", "asymptomatic infections", "primary infections by serotype", "FoI by serotype", "force of infection", "force of infection by serotype", and identified a significant gap in the current understanding of dengue epidemiology. Despite acknowledging the high prevalence of inapparent DENV infections in endemic regions, previous research has focused primarily on symptomatic infections, potentially biasing our understanding of the DENV epidemiological landscape and hindering our capacity to determine the complete disease spectrum of the different DENV serotypes. While cross-sectional studies have provided preliminary insights into this gap, there is a need for more comprehensive and detailed serotype-specific insights to evaluate the epidemiological impact of inapparent infections. The lack of comprehensive characterization of inapparent infections reflects methodological challenges, particularly the need for prospective cohort studies designed to capture and accurately serotype these infections. Moreover, the reliance on labor-intensive and low-throughput antibody neutralization assays for serotyping, despite their accuracy, has constrained high-throughput analysis required for large-scale epidemiological studies.Added value of this study: Our study, spanning 17 years of prospective cohort data in Nicaragua, addresses this bottleneck in dengue research by providing a detailed examination of primary inapparent infections. The introduction of a novel envelope domain III (EDIII) multiplex microsphere-based assay for DENV serotyping represents a significant methodological advance, offering an efficient, scalable alternative for large epidemiological studies. A key contribution of our study is the intricate pattern of serotype distribution among inapparent infections. In contrast to the serotype predominance observed in symptomatic infections, inapparent infections exhibit a complex landscape with co-circulation of multiple DENV serotypes, including serotypes undetected in symptomatic surveillance in multiple years. Our systematic documentation of the entire disease spectrum provides unprecedented insights into the serotype-specific disease burden in primary infection, including the proportion of symptomatic versus inapparent infection and its temporal variations, thus providing a more complete picture of DENV epidemiology than has been available to date. Notably, we demonstrate striking differences in disease severity by serotype, with DENV3 infections being significantly more symptomatic and more severe compared to DENV1 and DENV2, the latter displaying the highest rate of inapparent infection.Implications of all the available evidence: Our research challenges prior assumptions by demonstrating that inapparent and symptomatic primary DENV infections present distinct epidemiological profiles, revealing that the epidemiological footprint of DENV is broader and more nuanced than previously recognized through symptomatic cases alone. These findings underscore the utility for continuous and comprehensive surveillance systems that capture both symptomatic and inapparent infections to accurately assess the epidemiological burden of DENV and inform public health interventions. Additionally, they provide critical insight for enhancing the accuracy of predictive DENV transmission modeling. Furthermore, the marked differences in infection outcomes by serotype emphasize the need for serotype-informed public health strategies. This nuanced understanding is pivotal for the crafting of targeted interventions, vaccine development and vaccination strategies, and efficient resource allocation, ultimately contributing to the global effort to mitigate the impact of dengue.
RESUMEN
Serological surveillance studies of infectious diseases provide population-level estimates of infection and antibody prevalence, generating crucial insight into population-level immunity, risk factors leading to infection, and effectiveness of public health measures. These studies traditionally rely on detection of pathogen-specific antibodies in samples derived from venipuncture, an expensive and logistically challenging aspect of serological surveillance. During the COVID-19 pandemic, guidelines implemented to prevent the spread of SARS-CoV-2 infection made collection of venous blood logistically difficult at a time when SARS-CoV-2 serosurveillance was urgently needed. Dried blood spots (DBS) have generated interest as an alternative to venous blood for SARS-CoV-2 serological applications due to their stability, low cost, and ease of collection; DBS samples can be self-generated via fingerprick by community members and mailed at ambient temperatures. Here, we detail the development of four DBS-based SARS-CoV-2 serological methods and demonstrate their implementation in a large serological survey of community members from 12 cities in the East Bay region of the San Francisco metropolitan area using at-home DBS collection. We find that DBS perform similarly to plasma/serum in enzyme-linked immunosorbent assays and commercial SARS-CoV-2 serological assays. In addition, we show that DBS samples can reliably detect antibody responses months postinfection and track antibody kinetics after vaccination. Implementation of DBS enabled collection of valuable serological data from our study population to investigate changes in seroprevalence over an 8-month period. Our work makes a strong argument for the implementation of DBS in serological studies, not just for SARS-CoV-2, but any situation where phlebotomy is inaccessible. IMPORTANCE Estimation of community-level antibody responses to SARS-CoV-2 from infection or vaccination is critical to inform public health responses. Traditional studies of antibodies rely on collection of blood via venipuncture, an invasive procedure not amenable to pandemic-related social-distancing measures. Dried blood spots (DBS) are an alternative to venipuncture, since they can be self-collected by study participants at home and do not require refrigeration for shipment or storage. However, DBS-based assays to measure antibody levels to SARS-CoV-2 have not been widely utilized. Here, we show that DBS are comparable to blood as a sampling method for antibody responses to SARS-CoV-2 infection and vaccination over time measured using four distinct serological assays. The DBS format enabled antibody surveillance in a longitudinal cohort where study participants self-collected samples, ensuring the participants' safety during an ongoing pandemic. Our work demonstrates that DBS are an excellent sampling method for measuring antibody responses whenever venipuncture is impractical.
