The NS1 antigen of dengue virus is detected in serum during which time window post-illness onset, and its detection serves which diagnostic purpose?

• A Days 5–14; marks dengue haemorrhagic fever differentiation from dengue fever
• B Days 7–21; indicates secondary dengue infection with higher antibody titers
• C Days 1–5; detects early viraemia as a surrogate for viral antigen before antibody seroconversion ✓
• D Persists for 3 months; used for longitudinal monitoring of dengue severity

Explanation

The dengue NS1 (non-structural protein 1) antigen is secreted abundantly from virus-infected cells and is detectable in serum from approximately day 1 of fever until day 9 (declining as antibodies rise). It serves as an early diagnostic marker in the febrile/viraemic phase (days 1–5) before IgM antibodies become detectable, bridging the gap between PCR availability and clinical need. NS1 ELISA has good sensitivity and specificity in primary dengue infections; sensitivity is lower in secondary infections. It does not differentiate dengue haemorrhagic fever from dengue fever or indicate infection type.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.