Below is a concise but complete paediatric reference for major childhood viral and bacterial exanthematous infections commonly tested in paediatrics.
Childhood Infections in Paediatrics
(Measles, Scarlet Fever, Rubella, Erythema Infectiosum, Roseola Infantum, HFMD, Varicella)
1. Measles (Rubeola)
Definition
A highly contagious viral infection caused by the measles virus (Paramyxovirus family) characterized by fever, cough, coryza, conjunctivitis and maculopapular rash.
Pathophysiology
- Virus spreads through respiratory droplets
- Replication occurs in respiratory epithelium
- Dissemination through lymphatics and blood
- Causes immune suppression and epithelial damage
- Leads to systemic rash and respiratory symptoms
Causes / Risk Factors
- Unvaccinated children
- Crowded living conditions
- Malnutrition (especially vitamin A deficiency)
- Poor immunization coverage
Clinical Features
Prodromal Phase (3–5 days)
- High fever
- Cough
- Coryza (runny nose)
- Conjunctivitis
- Koplik spots (white lesions on buccal mucosa)
Rash Phase
- Maculopapular rash
- Starts behind ears → face → trunk → limbs
- Rash becomes confluent
Other Symptoms
- Photophobia
- Lymphadenopathy
Complications
- Pneumonia (most common cause of death)
- Otitis media
- Diarrhea
- Encephalitis
- Subacute sclerosing panencephalitis (SSPE)
Investigations
- Clinical diagnosis
- Measles IgM antibodies
- PCR testing
- CBC (leukopenia common)
Management
Supportive
- Hydration
- Antipyretics
- Nutrition
Vitamin A Therapy
Indication: All children with measles
Dose:
- <6 months: 50,000 IU
- 6–11 months: 100,000 IU
- ≥12 months: 200,000 IU for 2 days
Isolation
- Prevent spread
Prevention
- MMR vaccine
- Given at 9–12 months and booster later
2. Scarlet Fever
Definition
An acute bacterial illness caused by Group A Streptococcus (Streptococcus pyogenes) producing erythrogenic toxins leading to rash.
Pathophysiology
- Streptococcal infection of throat
- Bacteria release exotoxins
- Causes diffuse erythematous rash
Clinical Features
- Fever
- Sore throat
- Vomiting
Rash
- Fine sandpaper-like rash
- Starts on neck and chest
- Spreads to trunk and limbs
Characteristic Signs
- Strawberry tongue
- Circumoral pallor
- Pastia lines (rash in skin folds)
Desquamation
Peeling of skin after rash fades.
Investigations
- Throat swab
- Rapid antigen test
- CBC (neutrophilia)
Management
Antibiotic
Drug: Penicillin V
Indication: Streptococcal infection
Dose
- Children: 250 mg orally 2–3 times daily for 10 days
Mechanism
- Inhibits bacterial cell wall synthesis
Adverse Effects
- Allergy
- Rash
- GI upset
Alternative
- Amoxicillin
- Azithromycin (penicillin allergy)
Complications
- Rheumatic fever
- Post-streptococcal glomerulonephritis
- Otitis media
3. Rubella (German Measles)
Definition
A viral infection caused by rubella virus producing mild rash and lymphadenopathy.
Transmission
Respiratory droplets
Pathophysiology
Virus infects respiratory tract → spreads via bloodstream → rash.
Clinical Features
Prodrome
- Mild fever
- Malaise
- Lymphadenopathy
Rash
- Pink maculopapular rash
- Starts on face
- Spreads to trunk
Characteristic
- Postauricular and occipital lymphadenopathy
Complications
- Arthritis
- Thrombocytopenia
- Encephalitis
Congenital Rubella Syndrome
If infection occurs during pregnancy.
Features
- Cataracts
- Deafness
- Heart defects
- Intellectual disability
Diagnosis
- Rubella IgM antibodies
- PCR
Management
Supportive treatment.
Prevention
MMR vaccine
4. Erythema Infectiosum (Fifth Disease)
Definition
A viral infection caused by Parvovirus B19.
Pathophysiology
Virus infects erythroid precursor cells in bone marrow.
Clinical Features
Stage 1
- Mild fever
- Malaise
Stage 2
Characteristic “Slapped cheek” rash
Stage 3
- Lace-like rash on trunk and limbs
Complications
- Aplastic crisis in hemolytic anemia
- Fetal hydrops in pregnancy
- Chronic anemia in immunocompromised
Investigations
- Parvovirus B19 IgM
- PCR
Management
Supportive care.
5. Roseola Infantum (Exanthem Subitum)
Definition
A viral illness caused by Human Herpesvirus-6 (HHV-6).
Age
Usually 6 months – 2 years
Pathophysiology
Virus infects T-lymphocytes → systemic infection.
Clinical Features
Phase 1
- High fever (39–40°C) for 3–5 days
- Child otherwise well
Phase 2
After fever subsides → rash appears.
Rash
- Pink maculopapular rash
- Begins on trunk
- Spreads to neck and limbs
Complications
- Febrile seizures
Diagnosis
Clinical.
Management
Supportive care.
6. Hand Foot and Mouth Disease (HFMD)
Definition
A viral illness caused by Coxsackievirus A16 or Enterovirus 71.
Transmission
Fecal-oral route and respiratory droplets.
Clinical Features
- Fever
- Sore throat
- Reduced appetite
Rash
- Vesicular lesions on:
* Hands
* Feet
* Mouth
Oral Lesions
Painful ulcers on tongue and buccal mucosa.
Complications
Rare but include:
- Viral meningitis
- Encephalitis
Diagnosis
Clinical.
Management
- Hydration
- Pain control
- Soft diet
7. Varicella (Chickenpox)
Definition
A highly contagious viral infection caused by Varicella Zoster Virus (VZV).
Transmission
Respiratory droplets or direct contact.
Pathophysiology
Virus replicates in respiratory tract → viremia → skin lesions.
Clinical Features
Prodrome
- Fever
- Malaise
- Headache
Rash
Classic “dew drop on rose petal” vesicles.
Lesions appear in different stages simultaneously:
- Macules
- Papules
- Vesicles
- Crusts
Distribution
- Trunk > face > limbs.
Complications
- Secondary bacterial infection
- Pneumonia
- Encephalitis
- Cerebellar ataxia
Investigations
Usually clinical.
Management
Supportive
- Calamine lotion
- Antihistamines
- Antipyretics
Antiviral
Drug: Acyclovir
Indication
Severe disease or immunocompromised children.
Mechanism
Inhibits viral DNA polymerase.
Dose
- Children: 20 mg/kg per dose orally 4 times daily for 5 days
Adverse Effects
- Nausea
- Headache
- Renal toxicity (rare)
Prevention
Varicella vaccine
Quick Comparison Table
| Disease | Causative Agent | Rash Pattern | Key Feature |
| ------------- | ---------------------- | -------------------- | ------------------------- |
| Measles | Measles virus | Face → body | Koplik spots |
| Scarlet fever | Streptococcus pyogenes | Sandpaper rash | Strawberry tongue |
| Rubella | Rubella virus | Face → trunk | Lymphadenopathy |
| Fifth disease | Parvovirus B19 | Slapped cheek | Lacy rash |
| Roseola | HHV-6 | After fever subsides | High fever first |
| HFMD | Coxsackievirus | Hands, feet, mouth | Vesicles |
| Varicella | Varicella zoster virus | Trunk dominant | Vesicles different stages |
If you want, I can also give MCQs, exam-important differences, and mnemonic tricks for these childhood rashes (very useful for paediatrics exams).
