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.
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 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.
Key medicines
Red-cell transfusion for B19 aplastic crisisSelect component, volume and transfusion rate with haematology according to haemodynamics, symptoms, baseline haemoglobin and haemoglobinopathy phenotype; use an emergency major-haemorrhage route if shock prevents full matching.
Intravenous immunoglobulin for persistent B19Use an infection and haematology agreed weight-based course for PCR-confirmed persistent B19 pure red-cell aplasia in immune deficiency; total dose, divided schedule and retreatment are protocol dependent.