Parvovirus B19 and enterovirus infection

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Parvovirus B19 is a small single-stranded DNA virus spread mainly by respiratory secretions and occasionally through blood products or vertical transmission. It binds globoside P antigen on erythroid progenitors and temporarily arrests erythropoiesis. Antibody formation clears viraemia and creates immune-complex rash or arthralgia; consequently the familiar rash usually appears after peak infectiousness.

The host determines B19 severity. A healthy child tolerates a short interruption in erythropoiesis, but a patient with chronic haemolysis exhausts circulating red cells quickly and develops transient aplastic crisis. An immunodeficient patient may not make neutralising antibody, allowing persistent viraemia and pure red-cell aplasia. Fetal infection damages rapidly expanding erythroid tissue, causing profound anaemia, cardiac failure and hydrops rather than a characteristic congenital-malformation syndrome.

Enteroviruses are non-enveloped positive-sense RNA viruses within the picornavirus family, including coxsackieviruses, echoviruses, numbered enteroviruses and polioviruses. Faecal-oral, respiratory and close-contact transmission seeds the oropharynx or gut, followed by viraemia. Tissue tropism explains mucocutaneous disease, meningitis, encephalitis, myocarditis, neonatal sepsis and anterior-horn or spinal-cord injury.

The practical distinction is between a self-limited syndrome and organ-threatening infection. A well child with hand-foot-mouth disease usually needs hydration and analgesia, whereas a shocked neonate, myocarditis or acute flaccid weakness needs intensive physiological support before viral confirmation. Sample the involved compartment, but remember that enterovirus D68 may be found in respiratory samples and not CSF, while stool remains essential to exclude poliovirus in paralysis.

Key points

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.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

B19 respiratory exposure

Respiratory droplets and close household or school contact spread parvovirus during viraemia before the characteristic rash becomes visible.

B19 vertical transmission

Maternal viraemia crosses the placenta and infects fetal erythroid cells, with greatest clinically important anaemia risk during earlier gestation.

Enterovirus faecal-oral spread

Virus shed in stool contaminates hands, surfaces, food and water, sustaining transmission after acute respiratory or mucocutaneous symptoms improve.

Enterovirus respiratory spread

Respiratory secretions transmit several types, especially EV-D68, while peripartum maternal infection can expose a vulnerable neonate.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Erythroid precursor arrest
B19 uses P antigen to enter dividing erythroid progenitors, causing cell death and a temporary collapse in reticulocyte production.
2
Immune-complex inflammation
Antibody binding during viral clearance generates the lacy exanthem and symmetrical arthropathy after peak viraemia has passed.
3
Enterovirus viraemia
Replication in pharyngeal or intestinal lymphoid tissue is followed by blood dissemination to skin, meninges, myocardium, liver or motor neurons.
4
Motor-system injury
Poliovirus and some non-polio enteroviruses injure anterior horn cells or spinal grey matter, producing asymmetric flaccid weakness and respiratory failure.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Erythema infectiosum

Mild fever and coryza precede bright cheek erythema and a reticular lacy rash on limbs and trunk that can recur with heat or exercise.

B19 arthropathy

Adults, particularly women, develop acute symmetrical pain and stiffness in hands, wrists, knees or ankles, sometimes without a recognisable rash.

Transient aplastic crisisRed flag

A patient with chronic haemolysis develops abrupt pallor, fatigue, dyspnoea and tachycardia with haemoglobin below baseline and profound reticulocytopenia.

Hand-foot-mouth disease

Fever, sore mouth and painful oral ulcers accompany papules or vesicles on palms, soles and sometimes buttocks or groin.

Enteroviral meningitisRed flag

Fever, headache, photophobia, vomiting and neck stiffness occur with lymphocytic CSF, while infants may show irritability, poor feeding or a bulging fontanelle.

Neonatal enterovirusRed flag

Sepsis-like collapse, hepatitis, coagulopathy, thrombocytopenia, encephalitis, pneumonitis or myocarditis develops in the first weeks after perinatal transmission.

Acute flaccid myelitisRed flag

Asymmetric limb weakness with reduced tone and reflexes follows a febrile respiratory illness and may include neck, bulbar or respiratory muscle involvement.

Red flags requiring action

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.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
FBC and reticulocyte countFirst step
Why
Identify B19-related interruption of red-cell production and quantify physiological risk.
Interpretation and limitations
A haemoglobin fall with marked reticulocytopenia supports aplastic crisis or pure red-cell aplasia; compare with baseline and examine spleen because sequestration usually retains a marrow reticulocyte response.
02
Parvovirus B19 IgM and IgG
Why
Determine recent infection, past immunity or susceptibility in an immunocompetent person or pregnancy.
Interpretation and limitations
IgM supports recent infection and IgG without IgM usually indicates past immunity; repeat paired samples after a recent exposure when both are negative, and use stored booking serum to clarify timing in pregnancy.
03
Parvovirus B19 PCR
Why
Detect viraemia when antibody testing may fail or marrow disease is acute or persistent.
Interpretation and limitations
High viral load supports acute infection during aplastic crisis or chronic replication in immune deficiency; low-level DNA can persist, so interpret with reticulocytes, serology and clinical course.
04
Fetal ultrasound and MCA Doppler
Why
Detect anaemia, cardiac strain and hydrops after confirmed maternal B19 infection.
Interpretation and limitations
Serial middle cerebral artery peak systolic velocity and ultrasound assess evolving fetal anaemia; hydrops or MCA velocity above the specialist threshold prompts urgent tertiary fetal-medicine assessment for blood sampling and transfusion.
05
CSF examination and enterovirus PCR
Why
Distinguish enteroviral CNS infection from bacterial meningitis and other encephalitis causes.
Interpretation and limitations
Lymphocytic pleocytosis with normal glucose supports viral meningitis, but early neutrophils occur and PCR can be negative; culture, bacterial PCR and empirical antibacterial decisions remain clinically driven.
06
Site-specific enterovirus PCR
Why
Confirm mucocutaneous, respiratory, myocardial, neonatal or disseminated enterovirus infection.
Interpretation and limitations
Use throat, vesicle, stool, blood, respiratory or tissue samples matched to syndrome and timing; arrange reference typing when severe disease, an outbreak or unusual neurological disease makes genotype important.
07
AFP and AFM reference specimen set
Why
Exclude poliovirus and identify non-polio enteroviruses in acute flaccid weakness.
Interpretation and limitations
Send two unadulterated stool specimens 24 to 48 hours apart within two weeks, throat swab or nasopharyngeal aspirate and any CSF to UKHSA with the required surveillance form.
08
Cardiac and neonatal organ assessment
Why
Stage myocarditis or disseminated neonatal enterovirus and direct critical support.
Interpretation and limitations
Obtain ECG, troponin, natriuretic peptide, echocardiography, blood gases, glucose, coagulation, liver and renal tests, cultures and viral PCR; normal early troponin does not exclude evolving myocardial dysfunction.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Splenic sequestration

An enlarging spleen, acute anaemia and a preserved or raised reticulocyte response favour sequestration over B19 marrow arrest.

Measles or rubella

Cough, coryza and conjunctivitis suggest measles, while posterior auricular nodes suggest rubella; both require notification pathways unlike routine B19.

HSV encephalitis

Focal seizure, temporal features and altered behaviour demand empirical aciclovir and CSF HSV testing while enterovirus remains in the panel.

Guillain-Barré syndrome

Ascending symmetrical weakness, sensory symptoms and demyelinating or axonal neurophysiology favour peripheral neuropathy over spinal grey-matter myelitis.

Bacterial meningitis

Shock, purpura, low CSF glucose or neutrophilic inflammation requires immediate antibacterial treatment because early enteroviral CSF can also contain neutrophils.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01APLASIARestore oxygen deliveryFirst stepA person with chronic haemolytic anaemia has acute symptomatic anaemia and a very low reticulocyte count.

1Assess ABCDE, oxygenation, haemodynamic status, haemoglobin change from baseline, reticulocytes, spleen size and concurrent fever or sepsis.
2Send parvovirus IgM, IgG and PCR, group and crossmatch blood, and use appropriate isolation around pregnant, haemolytic and immunocompromised contacts while viraemia is high.
3Transfuse phenotype-matched red cells according to symptoms, haemodynamics, baseline haemoglobin and the haemoglobinopathy specialist plan rather than a single generic threshold.
4Trend haemoglobin and reticulocyte recovery, identify exposed high-risk household members and involve haematology if suppression persists or multiple cell lines fall.

02PREGNANCYDetect fetal anaemiaA pregnant patient has a B19-compatible rash, exposure or positive recent-infection serology.

1Record gestation, exposure and symptom dates, test B19 IgG and IgM promptly and compare with stored booking serum when available.
2If initially IgG and IgM negative after a recent exposure, repeat serology at the locally specified interval because the first sample may precede seroconversion.
3Refer confirmed recent infection to fetal medicine for serial ultrasound and MCA Doppler, commonly every one to two weeks through the 8- to 12-week risk period.
4EscalationEscalate hydrops or Doppler evidence of severe fetal anaemia to a tertiary unit for fetal blood sampling and possible intrauterine transfusion.

03MENINGITISExclude bacteria safelyFever, headache, neck stiffness or an infant meningitis syndrome suggests enteroviral CNS infection.

1Stabilise the patient, obtain blood cultures and give immediate empirical antibacterial treatment when bacterial meningitis cannot safely be excluded.
2Perform lumbar puncture unless contraindicated, sending cells, protein, glucose, bacterial culture or PCR and enterovirus plus relevant HSV or VZV PCR.
3Provide fluids, analgesia, antiemesis and seizure care; stop antibiotics only after clinical, CSF and microbiological evidence adequately excludes bacterial disease.
4Investigate encephalopathy, focal signs, myocarditis, immune deficiency or prolonged symptoms beyond an uncomplicated meningitis pathway.

04NEONATESupport disseminated diseaseA neonate has sepsis-like illness, myocarditis, hepatitis, coagulopathy, meningitis or maternal peripartum enterovirus illness.

1Start neonatal sepsis resuscitation and empirical antibacterial therapy while obtaining blood, CSF, respiratory and stool viral PCR alongside cultures.
2Monitor ECG, echocardiography, lactate, glucose, coagulation, liver, renal and neurological status and involve neonatal intensive care early.
3Provide ventilation, vasoactive support, correction of coagulopathy and extracorporeal or advanced cardiac support where indicated; no routine antiviral has proven standard efficacy.
4Discuss intravenous immunoglobulin with neonatal infection specialists for severe disseminated disease, recognising that evidence, dose and benefit vary by syndrome and protocol.

05PARALYSISNotify and sample completelyAcute flaccid paralysis or myelitis lacks a clear non-infectious explanation.

1Measure respiratory function and bulbar safety repeatedly, obtain urgent spinal and brain imaging and involve neurology plus intensive care before weakness ascends.
2Notify the local health protection team urgently, record polio vaccination, travel and respiratory prodrome, and use standard, contact and droplet precautions.
3Send two stool samples 24 to 48 hours apart, throat or nasopharyngeal sample and any CSF to the UKHSA reference laboratory with the E72 pathway.
4Continue electrophysiology, MRI and immune investigations for transverse myelitis, Guillain-Barré syndrome and other mimics while rehabilitation and complication prevention begin.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Restores oxygen-carrying capacity while marrow erythropoiesis remains temporarily suppressed by acute parvovirus B19 infection.

Red-cell transfusion for B19 aplastic crisis

Select 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.

Avoid raising haemoglobin above the disease-specific safe range, particularly in sickle cell disease; check alloantibodies, phenotype matching, previous reactions, volume status and post-transfusion haemoglobin.

Provides neutralising antibody when the host cannot clear chronic parvovirus viraemia and transfusion-dependent red-cell aplasia.

Intravenous immunoglobulin for persistent B19

Use 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.

Confirm ongoing viral causation first; monitor infusion reaction, thrombosis, haemolysis, renal injury and volume load, and reduce immunosuppression only with the responsible specialist.

Relieves fever, sore mouth, headache, arthralgia and myalgia in uncomplicated B19 or enterovirus infection while hydration is maintained.

Paracetamol

Give 500 mg to 1 g orally every four to six hours when required, to a maximum of 4 g in 24 hours for a typical adult; use weight-based paediatric dosing.

Reduce the maximum dose in adults below 50 kg or with malnutrition, harmful alcohol use or liver disease, and check all combination preparations for duplicate paracetamol.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Aplastic crisis

Temporary marrow arrest causes life-threatening anaemia in chronic haemolysis and may require urgent phenotype-matched red-cell transfusion.

Persistent red-cell aplasia

Failed antibody clearance during immune deficiency permits chronic B19 viraemia, severe reticulocytopenic anaemia and repeated transfusion dependence.

Fetal hydrops

Profound fetal anaemia causes high-output cardiac failure, oedema, effusions, placentomegaly, intrauterine death or urgent need for transfusion.

Enteroviral organ failure

Myocarditis, hepatitis, coagulopathy, pneumonitis, encephalitis and neonatal shock can progress rapidly despite initially non-specific fever and malaise.

Permanent motor disability

Anterior horn or spinal-cord injury in poliomyelitis or acute flaccid myelitis leaves weakness, contracture, ventilatory dependence and long rehabilitation needs.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

In aplastic crisis, repeat haemoglobin and reticulocytes until marrow recovery is clear, while monitoring oxygen delivery, transfusion response and any concurrent sequestration or haemolysis.
After confirmed maternal B19 infection, follow the fetal-medicine ultrasound and MCA Doppler schedule for the entire delayed anaemia window, not merely until maternal symptoms resolve.
During enteroviral meningitis, reassess consciousness, seizures, sodium, hydration and culture results; unexpected progression should prompt imaging and alternative pathogen or inflammatory investigation.
In neonatal enterovirus, trend lactate, cardiac output, ECG, troponin, liver function, coagulation, glucose and viral burden alongside the response of each failing organ.
For acute flaccid weakness, serially measure forced vital capacity, cough, swallow, autonomic function and limb power, with early rehabilitation and pressure-area or thrombosis prevention.
Persistent B19 anaemia requires serial PCR, haemoglobin and reticulocytes plus review of immune recovery and transfusion dependence after immunoglobulin treatment.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Rash follows viraemia

The B19 rash is largely immune mediated and often appears as viraemia falls, so the visibly rashy child is usually less infectious than during the preceding prodrome.

Reticulocytes separate crises

A very low reticulocyte count points to parvovirus marrow arrest, whereas splenic sequestration and haemolysis usually provoke increased reticulocyte production.

Hydrops is treatable

B19 fetal anaemia can drive high-output failure and hydrops, but timely Doppler detection permits specialist intrauterine transfusion rather than assuming inevitable loss.

CSF can miss enterovirus

Some neurotropic enteroviruses, particularly EV-D68, are rarely found in CSF, making respiratory and stool specimens essential in flaccid paralysis.

Polio exclusion stays mandatory

UK polio-free status depends on complete surveillance, so vaccination history never replaces paired stool sampling and notification of unexplained acute flaccid paralysis.

11Common pitfallsFrequent interpretation and management errors.

01
Do not assume an aplastic crisis will show the slapped-cheek rash; marrow suppression often occurs during viraemia before rash or antibody develops.
02
Do not confuse aplastic crisis with splenic sequestration without checking spleen size and reticulocytes, because immediate management and transfusion planning differ.
03
Do not reassure a pregnant patient from mild symptoms alone; confirmed recent B19 infection needs fetal surveillance for delayed anaemia and hydrops.
04
Do not stop empirical meningitis antibiotics merely because enterovirus PCR was requested; bacterial disease must be safely excluded from the complete evidence.
05
Do not rely on CSF alone in acute flaccid paralysis; paired stool and respiratory samples are essential for polio and non-polio enterovirus surveillance.
06
Do not label a shocked neonate with a positive enterovirus result as having a benign viral illness; myocarditis and hepatitis require intensive organ support.