| Agent | Togavirus (RNA) | Paramyxovirus (RNA) | S. pyogenes (GAS) exotoxin | Parvovirus B19 (DNA) | HHV-6, HHV-7 (DNA) | VZV (HHV-3) (DNA) |
| Prodrome | Low-grade fever, postauricular/occipital LAD, arthralgias. | 3 C’s: Cough, Coryza, Conjunctivitis. High fever. | Fever, pharyngitis, headache, vomiting. | Mild flu-like sx. | High fever (>40°C) for 3-5 days, child appears well. | Fever, malaise. |
| Enanthem | Forchheimer spots (petechiae on soft palate) | Koplik spots (blue-white spots on buccal mucosa). Pathognomonic. | Strawberry tongue, palatal petechiae. | N/A | Nagayama spots (papules on soft palate). | Ulcers in mouth/pharynx. |
| Exanthem | Maculopapular rash starts on face, spreads caudally in <24h. Lighter than measles. | Maculopapular rash starts at hairline, spreads caudally. Confluent. | ”Sandpaper” texture, diffuse erythema. Starts on trunk, spreads out. Spares palms/soles. Circumoral pallor. | ”Slapped cheeks” (malar rash), followed by lacy, reticular rash on trunk/extremities. | Maculopapular rash appears as fever breaks. Starts on trunk, spreads to face/extremities. | Vesicular rash on erythematous base (“dew drop on a rose petal”). Lesions in different stages. Starts on trunk, spreads to face/limbs. |
| Key Buzzwords | ”3-day measles”, postauricular LAD. Congenital: PDA, cataracts, deafness. | Koplik spots, 3 C’s, SSPE (late complication). | Sandpaper rash, strawberry tongue, Pastia’s lines (linear petechiae in flexures). | Slapped cheeks, aplastic crisis (in SCD), hydrops fetalis. | Fever first, then rash. Febrile seizures common. | Pruritic vesicles in crops, Tzanck smear shows multinucleated giant cells. Reactivates as shingles. |
| Tx | Supportive. MMR vaccine for prevention. | Supportive, Vit A. MMR vaccine for prevention. | Penicillin or Amoxicillin (to prevent rheumatic fever). | Supportive. | Supportive. | Supportive. Acyclovir in teens/adults/immunocompromised. Live-attenuated vaccine. |
