Dengue virus NS1 antigen-capture ELISA is useful in which phase of dengue fever for laboratory diagnosis?
- A After day 7 (recovery phase) when IgG titres are at their peak
- B During the first 5 days of illness (febrile phase) before antibody seroconversion ✓
- C Throughout the entire illness and into convalescence due to persistent antigenemia
- D Only in secondary dengue infection when IgG memory response is robust
Explanation
Dengue NS1 (non-structural protein 1) antigenemia occurs during the viraemic febrile phase — typically days 1–5 of illness — before IgM antibody seroconversion. NS1 ELISA has sensitivity of 60–90% during this window and can differentiate from other febrile illnesses. After day 5–7, IgM antibodies develop (primary dengue) or IgG titres rise rapidly from pre-existing memory (secondary dengue). NS1 levels fall as antibody-antigen complexes form. IgM/IgG ELISA is more useful in the second week. RT-PCR for dengue RNA is the most sensitive test in the first 4 days. The WHO dengue diagnostic algorithm recommends NS1 antigen + RT-PCR in the first 5 days, and serology after day 5.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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Written and medically reviewed by the StethoPrep medical team.