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Health condition · Paediatric · Clinically reviewed

Encephalitis in children, time-critical treatment and specialist paediatric care.

A rare but serious brain inflammation - suspected on fever, seizures and altered consciousness. Empirical aciclovir is started immediately.

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Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a UK paediatric clinician before publication.

  • 02

    Sourced from guidance

    Checked against NICE, RCPCH, BPAIIG, ABN and Encephalitis Society standards you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK paediatric practice including empirical aciclovir, autoantibody testing and specialist commissioned care.

Key facts

Paediatric encephalitis at a glance.

The essentials for parents and clinicians - what it is, what causes it in each age band, and how it is treated in the UK today.

  • What it is

    Inflammation of the brain in a child - infective, para-infective or autoimmune - that alters consciousness, behaviour or neurology.

  • How common

    Around 5 to 10 cases per 100,000 children each year in the UK, with higher rates in infants under one.

  • Main causes

    HSV, enterovirus and parechovirus in infants; HSV, VZV, EBV and mycoplasma in older children; autoimmune (anti-NMDAR, ADEM, MOGAD) at any age.

  • Key symptom mix

    Fever, reduced consciousness, seizures (up to 60%), behavioural change and focal neurology - bulging fontanelle in babies.

  • First-line drug

    Empirical intravenous aciclovir 20 mg/kg every 8 hours - started immediately, before results, and never delayed.

  • Where it is treated

    Specialist commissioned centres including Great Ormond Street, Alder Hey, Birmingham, Bristol, Newcastle and Cambridge.

Causes by age

Different ages, different culprits.

The likely causes shift with age - neonates, infants and older children each have their own pattern of infective and immune triggers.

  • Neonates

    HSV (perinatal - mandate testing and urgent aciclovir), enterovirus, parechovirus. Presentation is often non-specific with sepsis-like features.

  • Infants and toddlers

    HSV, enterovirus (including EV-A71 as a hand, foot and mouth complication), parechovirus, rotavirus, mumps and measles.

  • Older children

    HSV, VZV, EBV, mycoplasma - plus travel-related JE, tick-borne encephalitis (TBEV) and West Nile virus in relevant regions.

  • Immune-mediated

    ADEM (post-viral or post-vaccine), anti-NMDAR (may follow HSV), MOG-associated disease and aquaporin-4 (NMOSD).

How the diagnosis is made

From suspicion to a clear plan.

The steps a UK paediatric team will follow when encephalitis is suspected - assessment, investigation and specialist referral.

  1. 01

    Assessing

    Recognition and stabilisation

    ABC assessment, seizure control, glucose and empirical antimicrobials - encephalitis is a time-critical diagnosis.

  2. 02

    Assessing

    Bloods and cultures

    FBC, U&E, LFTs, glucose, CRP, blood culture, viral serology and paediatric inflammatory panel.

  3. 03

    Assessing

    Urgent neuroimaging

    MRI is preferred - CT is used when MRI cannot be obtained quickly or to rule out mass effect before lumbar puncture.

  4. 04

    Confirming

    Lumbar puncture and CSF

    White cell count, protein, glucose, viral PCR panel, autoantibodies and oligoclonal bands - the diagnostic cornerstone.

  5. 05

    Confirming

    EEG

    Detects encephalopathy, subclinical seizures and patterns suggestive of HSV or autoimmune encephalitis.

  6. 06

    Referral

    Specialist paediatric neurology

    Early referral to a commissioned centre for infectious diseases, neuroimmunology and neurorehabilitation input.

  7. 07

    Referral

    Notification and follow-up

    UKHSA notification where indicated, plus structured neurorehabilitation, schooling and psychology follow-up.

Typical timeline: recognition to empirical treatment within an hour, definitive testing over days.

Symptoms

What paediatric encephalitis looks like.

Fever with reduced consciousness, seizures and behavioural change - and the features that push the picture towards autoimmune disease.

  • Fever and irritability

    A febrile, unusually drowsy or inconsolable infant should prompt urgent paediatric assessment.

  • Reduced consciousness

    From drowsiness through to coma - a Glasgow Coma Scale drop is a red flag at any age.

  • Seizures

    Present in up to 60% - focal, generalised, subtle or status epilepticus, sometimes as the first sign.

  • Behavioural or personality change

    Regression, agitation, hallucinations, mutism or a striking shift in personality - common in autoimmune forms.

  • Focal neurology

    Weakness, cranial nerve signs, ataxia or speech disturbance - highly suggestive of encephalitis rather than a simple viral illness.

  • Bulging fontanelle in babies

    Raised intracranial pressure in an infant - a clinical emergency needing immediate transfer.

  • Post-viral or post-vaccine features

    Subacute focal signs a few days to weeks after a viral illness or vaccination point towards ADEM.

  • Red flag - dyskinesia and autonomic

    Orofacial dyskinesia, autonomic instability and regression in a child - think anti-NMDAR encephalitis.

Treatment

How paediatric encephalitis is treated.

Empirical aciclovir first, seizure control, targeted antimicrobials and immunotherapy for autoimmune disease - all within a specialist paediatric pathway.

  • Empirical IV aciclovir

    Weight-based 20 mg/kg every 8 hours, started immediately on suspicion. Continued for 14 to 21 days if HSV is confirmed. Never delayed for results.

  • Bacterial cover if uncertain

    Ceftriaxone plus amoxicillin under 3 months, with dexamethasone where bacterial meningitis is possible - stopped once CSF and cultures clarify the picture.

  • Anticonvulsants

    Prompt seizure control with benzodiazepines, levetiracetam or phenytoin - subclinical seizures are common on EEG.

  • Corticosteroids

    Selective use - central to ADEM and many autoimmune encephalitides, avoided in unconfirmed viral disease.

  • IVIG and plasma exchange

    First-line immunotherapy for autoimmune encephalitis, ADEM and MOGAD - given in specialist paediatric neurology centres.

  • Rituximab

    Second-line B-cell depletion for anti-NMDAR and refractory autoimmune encephalitis - initiated by specialist neuroimmunology teams.

  • PICU and supportive care

    Airway support, intracranial pressure management, temperature, glucose and nutrition - the backbone of severe cases.

  • Neurorehabilitation

    Specialist paediatric neurorehabilitation, education liaison and psychology - shapes long-term functional outcomes.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and international specialist consensus, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

If your child is unwell with fever, drowsiness, seizures or behavioural change, seek urgent medical review. Ring 999 or attend the nearest emergency department.

  • NICE. Meningitis (bacterial) and meningococcal disease: recognition, diagnosis and management (NG240).

  • RCPCH and BPAIIG. Management of suspected viral encephalitis in children - national guideline.

  • Association of British Neurologists. Diagnosis and management of acute encephalitis in adults and children.

  • International Encephalitis Consortium. Case definitions and diagnostic criteria for encephalitis.

  • UKHSA. Notifiable diseases and causative organisms - notification duties.

  • Encephalitis Society. Paediatric encephalitis information and family support.

Red flags

When a child needs urgent transfer.

The features that mandate PICU-level care, neurosurgical review or specialist paediatric neuroimmunology input.

  • Neonatal HSV suspicion

    Any neonate with encephalopathy, seizures, sepsis-like presentation or vesicles - test and treat as HSV until proven otherwise.

  • Coma or falling GCS

    A drop of two or more points, or GCS under 12, needs immediate PICU escalation and airway assessment.

  • Status epilepticus

    Prolonged or recurrent seizures without recovery - a neurological emergency needing anaesthetic-led control.

  • Raised intracranial pressure

    Bulging fontanelle, sunset eyes, unequal pupils or Cushing response - urgent neuroimaging and neurosurgical input.

  • Post-viral multifocal signs

    Subacute focal deficits with white-matter lesions on MRI - consider ADEM and paediatric neuroimmunology referral.

  • Dyskinesia and regression

    Orofacial or limb dyskinesia, mutism or autonomic instability - test for anti-NMDAR antibodies and start immunotherapy early.

  • Immunocompromised child

    Consider a broader differential including CMV, HHV-6, JC virus, toxoplasma and fungal causes - discuss with infectious diseases.

  • Travel or tick exposure

    Ask about JE-endemic travel, tick-borne encephalitis regions and West Nile exposure - guides testing and vaccination advice for siblings.

  • Suspected non-accidental injury

    Encephalopathy with unexplained retinal haemorrhages, bruising or fractures - safeguarding referral alongside medical care.

Recovery

After discharge, a family journey.

Cognitive, behavioural and physical recovery can stretch across many months. Specialist paediatric neurorehabilitation shapes outcomes as much as the acute treatment did.

A quiet reminder

Recovery is rarely a straight line.

Fatigue, mood dips and school anxiety are common. The Encephalitis Society and paediatric neuropsychology teams can be steady companions.

  1. 01 Recovery

    Give recovery a long runway

    Fatigue, headaches, sleep disturbance and mood changes often outlast the acute illness - expect months, not days.

  2. 02 Education

    Plan for school reintegration

    Cognitive, memory and behavioural changes are common - liaison between school, SENCO and neurorehab makes a real difference.

  3. 03 Family

    Look after siblings and parents

    The whole family carries the load - psychological support and Encephalitis Society peer networks help.

  4. 04 Follow-up

    Stay under specialist review

    Paediatric neurology, neuropsychology and rehab review - relapses and late complications need catching early.

Frequently asked

What parents most often ask.

Quick answers on causes, urgent treatment, ADEM, anti-NMDAR encephalitis and long-term outlook.

  • What is encephalitis in children?

    Encephalitis is inflammation of the brain. In children it can be caused by viruses such as HSV, enterovirus and parechovirus, by post-infectious autoimmune processes such as ADEM, or by antibody-mediated autoimmune encephalitis such as anti-NMDAR. It changes consciousness, behaviour or neurology and is a medical emergency.

  • How is it different from meningitis?

    Meningitis inflames the linings of the brain and causes headache, fever and neck stiffness. Encephalitis inflames the brain itself and causes altered consciousness, seizures and behavioural change. The two often overlap as meningoencephalitis and both need urgent hospital care.

  • Why is aciclovir started before results are back?

    Herpes simplex virus encephalitis is life-threatening and treatable. Every hour of delay worsens outcomes, so UK guidance is to start intravenous aciclovir on suspicion at 20 mg/kg every 8 hours and stop only once HSV has been reliably excluded.

  • What is ADEM?

    Acute disseminated encephalomyelitis is a post-infectious or, rarely, post-vaccine autoimmune inflammation of the brain and spinal cord. It typically follows a viral illness by days to weeks, shows multifocal white matter lesions on MRI and usually responds well to intravenous steroids, IVIG or plasma exchange.

  • What is anti-NMDAR encephalitis in children?

    An antibody-mediated autoimmune encephalitis that causes behavioural regression, seizures, dyskinesia, movement disorder and autonomic instability. In children it can be triggered by herpes simplex virus. It is treated with immunotherapy - steroids, IVIG or plasma exchange - and often rituximab.

  • What is the long-term outlook?

    Outcomes are variable. Many children recover fully or nearly so, but some are left with cognitive, behavioural, motor or seizure-related sequelae. Early recognition, empirical aciclovir, specialist commissioned care and structured paediatric neurorehabilitation give the best chance of a good outcome.

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