Synopsis
Recognise benign exanthems and dangerous marrow, fetal, cardiac, neonatal and neurological disease, select site-specific viral tests, and escalate acute flaccid paralysis correctly.
- Parvovirus B19 infects erythroid precursors, briefly stopping red-cell production; this is minor in most people but can cause catastrophic anaemia when red-cell survival is already short.
- Erythema infectiosum causes a slapped-cheek facial rash followed by a lacy limb or trunk eruption; adults more often develop symmetrical small-joint arthropathy.
- Aplastic crisis produces an acute haemoglobin fall with a very low reticulocyte count, unlike splenic sequestration or haemolysis where marrow reticulocyte output usually rises.
- Recent maternal B19 infection requires fetal-medicine surveillance with serial ultrasound and middle cerebral artery Doppler for fetal anaemia or hydrops; severe fetal anaemia may need intrauterine transfusion.
- Enteroviruses usually cause self-limited fever, hand-foot-mouth disease, herpangina or aseptic meningitis, but neonates and immunocompromised patients can develop disseminated disease.
- Enteroviral meningitis is diagnosed with CSF PCR after bacterial meningitis has been covered or excluded; treatment is usually supportive and antibiotics stop only when bacterial disease is safely ruled out.
- Acute flaccid paralysis or myelitis unexplained by a non-infectious cause is urgently notifiable in England and requires two stool samples 24 to 48 hours apart plus respiratory and available CSF samples.
- There is no routinely licensed specific antiviral or vaccine for non-polio enteroviruses or parvovirus B19, so organ support, blood products, immunoglobulin in selected immune deficiency and prevention of transmission are central.
Key red flags
Rapid flaccid limb weakness, reduced reflexes, bulbar symptoms or falling vital capacity requires emergency neurology, respiratory support and same-day health-protection notification.
A person with sickle cell disease, thalassaemia or hereditary spherocytosis who becomes profoundly pale, breathless or tachycardic with reticulocytopenia may have life-threatening parvovirus aplastic crisis.
Parvovirus rash or exposure during pregnancy, especially before 20 weeks, needs prompt serology and fetal-medicine referral if recent infection is confirmed.
A neonate with shock, hepatitis, coagulopathy, myocarditis, arrhythmia, encephalitis or sepsis-like illness may have disseminated enterovirus and needs immediate neonatal critical care.
Chest pain, syncope, arrhythmia, pulmonary oedema or cardiogenic shock after a febrile enteroviral illness suggests myocarditis rather than uncomplicated hand, foot and mouth disease.
Persistent severe anaemia with absent reticulocytes during immune suppression suggests chronic parvovirus pure red-cell aplasia and requires haematology and infection review.
A patient with chronic haemolysis develops abrupt pallor, fatigue, dyspnoea and tachycardia with haemoglobin below baseline and profound reticulocytopenia.
Investigation priorities
Identify B19-related interruption of red-cell production and quantify physiological risk.
Management branches
A person with chronic haemolytic anaemia has acute symptomatic anaemia and a very low reticulocyte count.
- Assess ABCDE, oxygenation, haemodynamic status, haemoglobin change from baseline, reticulocytes, spleen size and concurrent fever or sepsis.
- Send parvovirus IgM, IgG and PCR, group and crossmatch blood, and use appropriate isolation around pregnant, haemolytic and immunocompromised contacts while viraemia is high.
- Transfuse phenotype-matched red cells according to symptoms, haemodynamics, baseline haemoglobin and the haemoglobinopathy specialist plan rather than a single generic threshold.
- Trend haemoglobin and reticulocyte recovery, identify exposed high-risk household members and involve haematology if suppression persists or multiple cell lines fall.