A 40-year-old woman from a dengue-endemic region presents on day 3 of febrile illness. Serology shows dengue IgG strongly positive while IgM is barely detectable. Which statement best explains this pattern?

• A This indicates a primary dengue infection with a brisk anamnestic response
• B IgG dominance this early is characteristic of Japanese encephalitis cross-reactivity
• C This pattern excludes active dengue and suggests past vaccination only
• D This indicates a secondary heterologous dengue infection, which carries higher risk of severe disease ✓

Explanation

In secondary dengue infection, pre-existing cross-reactive IgG from a prior heterologous serotype rises rapidly and dominates the early antibody response, often before IgM becomes prominent. This anamnestic pattern correlates with antibody-dependent enhancement and a higher risk of severe dengue. In primary infection, IgM predominates and IgG appears late and at low titre. Cross-reactive flavivirus titres rise broadly, not selectively as isolated high IgG on day 3.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.