Overview: An emerging blind spot in dengue diagnostics
Recent correspondence highlights a critical flaw in routine dengue molecular surveillance: sylvatic dengue virus 2 (DENV-2) infections are being misclassified as “Undetermined Serotype” by commercial serotyping assays. This misclassification mirrors prior reports of assay failure against sylvatic DENV-2 strains, notably in Senegal, West Africa, suggesting a broader, global issue in dengue diagnostics. The consequence is a systematic underrecognition of sylvatic lineages within routine surveillance data, which can distort epidemiological pictures and hinder public health responses.
Why sylvatic DENV-2 matters in a largely urban landscape
DENV-2 circulates in two broad ecological contexts: urban/endemic lineages and sylvatic strains that maintain a distinct reservoir cycle in forested environments. While urban DENV-2 is the primary driver of human outbreaks, sylvatic strains represent a potential source of new spillover events and genetic diversity that could influence vector competence, transmission dynamics, and vaccine effectiveness. If diagnostic tools fail to recognize sylvatic DENV-2, researchers may overlook shifts in lineage prevalence, delaying insights into how sylvatic reservoirs contribute to human infections.
Technical drivers of misclassification in molecular serotyping
Commercial dengue molecular serotyping assays are designed to target conserved regions that differentiate dengue serotypes. However, sylvatic DENV-2 strains may harbor genetic variations in primer or probe binding sites that are not encompassed by existing assays. When the assay fails to robustly amplify these variants, samples can be relegated to an “Undetermined Serotype” result. This is not a reflection of sample quality alone but a warning that existing molecular tools do not adequately cover the full genetic diversity of DENV-2. The parallel observation of assay failure in Senegal reinforces the need to reassess serotyping panels as dengue evolves in nature.
Implications for surveillance data and outbreak response
Misclassification has tangible consequences. Surveillance dashboards that rely on serotype data inform risk assessments, vector control priorities, and targeted clinical management. If sylvatic DENV-2 infections are masked by an undetermined category, epidemiologists may underestimate the diversity of circulating lineages or misinterpret temporal patterns of transmission. This hampers real-time monitoring of sylvatic lineage prevalence and could delay detection of spillover events that seed urban outbreaks or alter population immunity profiles.
A path forward: refining molecular tools for comprehensive coverage
To close this diagnostic gap, several strategies warrant consideration. First, develop multiplex RT-qPCR assays that explicitly include both urban and sylvatic DENV-2 targets, increasing sensitivity to diverse strains without sacrificing specificity. Second, implement periodic revalidation of serotyping panels against a curated panel of reference sylvatic DENV-2 sequences to keep pace with viral evolution. Third, adopt sentinel surveillance that deliberately samples from forest-adjacent populations to map sylvatic-human interface dynamics. Finally, ensure open channels for data sharing and rapid updates to diagnostic protocols when new variants are detected, enabling a more resilient dengue surveillance system.
Implementation considerations and benefits
Practical deployment of updated assays should balance cost, turnaround time, and compatibility with existing laboratory workflows. Collaborations between public health agencies, diagnostic manufacturers, and academic groups can co-create multiplex assays that minimize disruption while expanding coverage. In the long term, incorporating sylvatic strains into routine quality control materials will improve confidence in serotype assignments and reduce the frequency of indeterminate results. Ultimately, updated diagnostic tools will enhance real-time monitoring of sylvatic lineages among recorded dengue infections, strengthening outbreak preparedness and informing vaccine and therapeutic strategies.
Conclusion: a call for proactive assay evolution
The misclassification of sylvatic DENV-2 as undetermined serotype is more than a technical glitch; it is a signal that dengue diagnostic tools must evolve alongside the virus. By expanding multiplex assays to include both urban and sylvatic strains and by instituting ongoing validation, the global health community can ensure surveillance systems reflect true viral diversity. Such improvements are essential for accurate epidemiology, timely public health responses, and a more complete understanding of dengue dynamics in a changing world.
