Fifth Disease (Erythrovirus B19 infection)
🦠 Erythrovirus B19 (formerly Parvovirus B19) causes Fifth disease.
It specifically infects erythroid progenitor cells, leading to transient erythroid hypoplasia and temporary failure of red blood cell production.
Aplastic crises occur particularly in patients with underlying haemolytic anaemias.
📖 About
- 🔬 Small, single-stranded, non-enveloped DNA virus (Parvoviridae family).
- 🎯 Targets erythroid lineage cells in bone marrow.
- 🌬️ Transmission: airborne droplets, blood products, and vertical (mother → fetus).
- 🧑🤝🧑 Most cases occur in childhood; adults may present differently (arthritis > rash).
🧬 Aetiology & Pathophysiology
- 🎯 Infects cells expressing the P antigen on erythroid precursors.
- ⛔ Individuals lacking P antigen = naturally resistant.
- 📉 Replicates in erythroid progenitors (E-CFU, E-BFU) → ↓ red cell, WCC & platelet production.
- ⚡ Triggers transient aplastic crises in haemolytic disorders (e.g. sickle cell, thalassaemia).
- 🤰 Vertical transmission may cause fetal anaemia or hydrops fetalis.
🩺 Clinical Presentation
- 🧒 Erythema infectiosum (“slapped cheek” syndrome) → bright red facial rash + lacy rash on trunk/limbs.
- 💉 Transient aplastic crisis in patients with haemolytic anaemias.
- 🤰 Pregnancy: risk of miscarriage, hydrops fetalis, severe fetal anaemia.
- 🦵 Arthralgia/arthritis: small joint pain/swelling (esp. adult women).
- 🧑⚕️ Immunocompromised: chronic anaemia due to failure to clear virus.
⚠️ Complications
- 🧒 Fifth disease → usually mild/self-limiting in children.
- 🧤🧦 “Gloves & Socks Syndrome” → painful purpuric rash on hands/feet in adolescents.
- 🩸 Pure red cell aplasia → can precipitate crisis in haemoglobinopathies.
- 🤰 Hydrops fetalis → severe fetal anaemia, high-output cardiac failure, intrauterine death.
🔎 Investigations
- 📉 FBC: Anaemia, leucopenia, thrombocytopenia; ↓ reticulocytes.
- 🧬 PCR: Detects viral DNA (gold standard in immunocompromised or pregnant women).
- 🧪 Serology: IgM = recent infection; IgG = immunity.
💊 Management
- 🩸 Blood transfusion: if aplastic crisis in haemolytic disease.
- 🤕 Supportive: self-limiting in immunocompetent; NSAIDs for arthralgia.
- 🤰 Pregnancy: IV immunoglobulin (IVIG) for severe maternal infection; intrauterine transfusion for affected fetus with hydrops.
- 🧑⚕️ Immunocompromised: IVIG may be required to clear persistent infection.
💡 Exam tip: Think Parvovirus B19 if a child presents with a “slapped cheek rash”,
or if a patient with sickle cell disease has sudden severe anaemia + ↓ reticulocyte count.
In pregnancy → always consider hydrops fetalis.
📚 References
