Introduction: The surveillance blind spot in dengue diagnostics
Dengue viruses are routinely monitored through molecular serotyping assays that identify circulating serotypes in patient samples. Recent work by Suppiah and colleagues highlights a significant blind spot: sylvatic dengue virus type 2 (DENV-2) strains are increasingly misclassified as “Undetermined Serotype” when using common commercial RT-qPCR serotyping assays. This misclassification mirrors findings from Senegal, West Africa, where sylvatic DENV-2 strains escaped detection by standard molecular tools. The consequence is a gap in understanding the true diversity of dengue infections and an underappreciation of sylvatic lineage prevalence in routine surveillance.
Why sylvatic DENV-2 matters for public health surveillance
Sylvatic DENV-2, circulating in non-human primates and sylvatic mosquito vectors, represents a genetic reservoir that can spill over into urban transmission cycles. If current diagnostic tools fail to identify these strains, public health authorities risk underestimating outbreak potential, misjudging serotype dynamics, and missing signals of spillover events. The accurate classification of DENV-2 is not merely a labeling problem; it informs vaccine strategy, vector control priorities, and hazard assessment for regions at risk of sylvatic–urban transmission interplay.
Limitations of existing assays: technical and epidemiological implications
Commercial serotyping assays are designed around known circulating strains, often focusing on urban lineages. When a sylvatic variant diverges at key primer or probe binding sites, it can be detected as a non-specific result or labeled as undetermined. This limitation has immediate epidemiological implications: surveillance data may appear to show stable serotype distributions while a hidden reservoir of DENV-2 continues to circulate in sylvatic transmission cycles. The resulting data gap can hinder timely detection of emerging spillover risks and reduce confidence in longitudinal dengue datasets used for vaccine impact assessments and risk mapping.
Recommendations: updating tools to include urban and sylvatic strains
To close this diagnostic gap, surveillance programs should consider the following actions:
- Develop multiplex assays that explicitly target both urban and sylvatic DENV-2 lineages, ensuring broad coverage of genetic diversity within serotype 2.
- Reassess primer and probe design to accommodate known sylvatic-Specific variants, validating assays against curated panels that include sylvatic strains from regions at risk of spillover (e.g., West Africa).
- Incorporate routine sequence-based confirmation (e.g., RT-qPCR with confirmatory sequencing) for samples initially reported as undetermined serotype, enabling real-time tracking of sylvatic lineage prevalence.
- Establish regional reference labs and data-sharing networks to harmonize assay performance metrics and to monitor shifts in dengue serotype dynamics across urban-sylvatic interfaces.
Implications for surveillance systems and research funding
Enhancing molecular diagnostics to recognize sylvatic DENV-2 will refine the quality of surveillance data and support better-informed public health decisions. It will also allow researchers to map the geographic and temporal spread of sylvatic lineages, assess spillover risk, and evaluate how environmental changes or vector behavior influence dengue epidemiology. Funding agencies should prioritize assay validation studies, cross-regional collaborations, and the development of open-access panels that include diverse sylvatic strains to improve global dengue surveillance equity.
Conclusion: A path toward more accurate, real-time dengue monitoring
The misclassification of sylvatic DENV-2 as undetermined serotype reveals a critical deficiency in current diagnostic tools. Updating RT-qPCR serotyping assays to encompass both urban and sylvatic lineages will enhance real-time surveillance, allow for better tracking of dengue dynamics, and improve preparedness for potential spillover events. As dengue viruses continue to adapt and circulate across ecologies, diagnostic inclusivity must accompany epidemiological vigilance.