Same Fever, Three Diseases

Brazil experiences co-circulation of dengue (4 serotypes), Zika, and chikungunya — all transmitted by the same Aedes mosquitoes, all presenting with similar acute-phase symptoms (fever, rash, joint pain, headache), and all requiring different clinical management. Dengue can be fatal if severe dengue is not recognized and fluid-managed; Zika is clinically mild but teratogenic in pregnancy; chikungunya causes chronic arthralgia requiring long-term management. In the acute febrile phase (first 3–5 days), no field-deployable diagnostic can reliably distinguish between them. Fiocruz's reference laboratories can differentiate using RT-PCR, but the volume of suspected cases during epidemic seasons overwhelms laboratory capacity — Brazil reported 4.2 million probable dengue cases in 2024 alone — and results arrive days after clinical decisions must be made.

Clinical management diverges critically: dengue patients need fluid monitoring and should avoid NSAIDs (which increase bleeding risk); chikungunya patients benefit from NSAIDs for pain management. A pregnant woman with Zika requires different counseling and monitoring than one with dengue. Without acute-phase differentiation, clinicians must treat empirically — which means either undertreating (missing severe dengue until hemodynamic instability) or overtreating (admitting all febrile patients for dengue monitoring when most have a different arbovirus). During the 2024 dengue outbreak, Brazilian health facilities in endemic states were overwhelmed by patients who needed assessment for severe dengue risk but many of whom had chikungunya or Zika. The inability to triage at point-of-care is a multiplier of health system strain.

Dengue NS1 rapid diagnostic tests (RDTs) detect dengue-specific antigen and are commercially available, but their sensitivity drops to 50–70% after day 3 of illness, and they say nothing about what a dengue-negative febrile patient has. IgM/IgG serological tests for all three viruses exist but cross-react extensively — antibodies to dengue, Zika, and chikungunya share epitopes due to flavivirus relatedness, producing false positives that are clinically useless. Fiocruz has developed multiplex RT-PCR assays that can distinguish all three viruses simultaneously, but these require laboratory equipment (thermal cyclers, extraction kits) and trained operators, limiting deployment to reference labs. The fundamental diagnostic challenge is that the viruses are closely related (dengue and Zika are both flaviviruses; chikungunya is an alphavirus but co-circulates in the same vector-host system), and the immune responses they provoke overlap significantly.

A multiplex point-of-care test that distinguishes dengue (and ideally dengue serotype), Zika, and chikungunya from a single blood sample within 30 minutes — without requiring laboratory equipment — would transform clinical management in co-endemic settings. Fiocruz researchers have identified isothermal amplification (LAMP, RPA) as the most promising platform because it eliminates the thermal cycler requirement. But multiplex isothermal amplification with specificity for closely related flaviviruses is technically challenging — current multiplex LAMP assays achieve ~85% sensitivity for individual viruses but haven't been validated as a panel. An alternative approach uses host biomarker signatures (the human immune response differs between infections) rather than pathogen detection — Fiocruz researchers have published on transcriptomic signatures that distinguish arbovirus infections, but translating these into a rapid test is at early research stage.

A diagnostics team could benchmark existing arbovirus rapid tests (NS1 RDTs, IgM combo tests) under co-circulation conditions using Fiocruz's banked serum panels to quantify cross-reactivity rates and clinical utility under realistic conditions. A molecular biology team could design and test a multiplex isothermal amplification assay targeting conserved and type-specific regions of dengue, Zika, and chikungunya genomes, optimizing for specificity in the presence of closely related viral RNA. An epidemiology team could model the clinical and health system impact of introducing a multiplex POC test — how many unnecessary admissions would be prevented, and how would triage efficiency change during epidemic peak periods?