The reasoning: measles
| Feature | Detail |
|---|---|
| Agent | Measles virus (paramyxovirus; single serotype) |
| Reservoir | Humans only; no carriers |
| Transmission | Airborne and droplet; R₀ 12–18 |
| Incubation | 10–14 days (to rash ≈ 14 days) |
| Communicability | 4 days before to 4 days after rash onset |
| Clinical | Prodrome (fever, 3 C's: cough, coryza, conjunctivitis; Koplik spots) → maculopapular rash from the face and behind the ears downwards on day 3–4 → fades with brownish staining and desquamation |
| Complications | Pneumonia (commonest cause of death), diarrhoea, otitis media, laryngotracheobronchitis, malnutrition, xerophthalmia/keratomalacia, encephalitis (≈ 1/1,000), SSPE (years later), immune amnesia |
| High‑risk groups | Under 5s, malnourished, vitamin A‑deficient, immunocompromised, adults |
| Treatment | Supportive; vitamin A on days 1 and 2 (< 6 months 50,000 IU; 6–11 months 1 lakh IU; ≥ 12 months 2 lakh IU; a third dose 2–4 weeks later if eye signs) |