A laboratory scientist compares two dengue patients from the same outbreak. Patient X, never previously exposed to dengue, shows detectable dengue-specific IgM by day 5 with low IgG. Patient Y, previously infected with a different dengue serotype, shows high IgG titres rising steeply by day 3 while IgM remains low. The serological pattern in Patient Y represents:

• A Primary dengue infection
• B Secondary dengue infection ✓
• C False positive result due to Japanese encephalitis cross-reactivity
• D Convalescent phase sampling artefact

Explanation

In secondary dengue, pre-existing cross-reactive IgG from prior flavivirus exposure rises rapidly and dominates, often exceeding IgM, whereas primary infection features a slow IgM rise peaking after day 5 with modest late IgG. The anamnestic IgG response in secondary infections underlies antibody-dependent enhancement and greater severity risk. Cross-reaction with Japanese encephalitis antibodies does occur but would not produce this characteristic early high IgG pattern.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.