Herpes simplex and herpes zoster

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

Map pain, prodrome and lesions. HSV clusters recur at a site innervated by the same ganglion and can involve lips, genitals, fingers or eczema. Zoster usually occupies one sensory dermatome with neuropathic pain, allodynia and lesions at several stages. In darker skin, background erythema may be subtle or violaceous; vesicle grouping, dermatomal geometry, tenderness and later pigment change remain visible.

Urgency is determined by structure and host. Examine eyes and vision when trigeminal skin is involved, inspect the ear canal and palate with facial weakness, ask about urinary retention in sacral disease and assess meningism or cognition. Disseminated zoster means lesions beyond the primary and adjacent dermatomes and is particularly dangerous in immune compromise.

Antivirals work best early but timing is not an absolute barrier in evolving high-risk disease. Choose oral treatment for eligible uncomplicated zoster and severe primary or frequent HSV according to the relevant pathway; use intravenous aciclovir for encephalitis, dissemination or inability to absorb under specialist care. Analgesia is active treatment, yet systemic corticosteroids are not routine zoster monotherapy and do not prevent post-herpetic neuralgia.

Key points

HSV typically causes recurrent grouped painful vesicles or erosions at a mucocutaneous site; zoster causes unilateral dermatomal pain followed by vesicles that usually do not cross the midline.
Swab a fresh vesicle base for PCR when diagnosis is uncertain, disease is severe or genital, or the result changes infection-control or specialist decisions.
Herpes zoster ophthalmicus, eye pain, photophobia or visual change requires same-day ophthalmic assessment; a normal-looking eye does not cancel symptoms.
Offer oral antivirals within 72 hours of zoster rash onset to people aged 50 or older and to younger people with ophthalmic, non-truncal, moderate-to-severe or immunocompromised disease.
Consider treatment up to seven days after onset when new vesicles continue or complication risk is high.
Aciclovir for zoster is 800 mg five times daily for seven days; valaciclovir 1 g three times daily for seven days improves dosing convenience.
Adjust aciclovir and valaciclovir for renal impairment, maintain hydration and review nephrotoxic medicines or new confusion.
Keep lesions covered, avoid pregnant non-immune people, neonates and severely immunocompromised contacts, and exclude from susceptible-care settings while lesions remain weeping.

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

Herpes simplex latency

HSV-1 or HSV-2 establishes sensory-ganglion latency after primary mucocutaneous infection and reactivates with variable triggers including illness, ultraviolet exposure, trauma and stress.

Varicella-zoster reactivation

After chickenpox, varicella-zoster virus persists in dorsal-root or cranial-nerve ganglia and reactivates as shingles when cell-mediated immunity declines.

Contact transmission

HSV spreads through direct contact with lesions or asymptomatic shedding; zoster vesicle fluid transmits varicella to a susceptible contact, not shingles itself.

Host risk

Older age, immune suppression, malignancy and immunomodulatory medicines increase zoster severity, dissemination and post-herpetic neuralgia risk.

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

1
Epidermal cytolysis
Viral replication creates clustered intraepidermal vesicles that become pustular, erode and crust, often with preceding pain, burning or paraesthesia.
2
Neural reactivation
Virus travels along a sensory nerve to skin, explaining recurrent HSV at a local mucocutaneous site and zoster within one dermatome.
3
Ganglion and nerve injury
Zoster inflammation damages sensory neurons, producing acute neuritis and sometimes persistent neuropathic pain after the rash heals.
4
Dissemination
Impaired cellular immunity permits widespread cutaneous and visceral replication with pneumonitis, hepatitis, encephalitis or severe mucosal disease.

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

Recurrent grouped HSV vesicles

Tingling or burning precedes tightly grouped vesicles that erode and recur at a familiar lip, genital or acral site.

Unilateral dermatomal zoster

Painful crops of vesicles follow one sensory band and stop near the midline, sometimes after several days of neuralgia.

Ophthalmic zosterRed flag

Forehead, upper-eyelid or nasal-tip vesicles with eye symptoms indicates trigeminal involvement and possible intraocular disease.

Ramsay Hunt syndromeRed flag

Severe ear pain, vesicles in ear or palate, ipsilateral facial palsy, vertigo or hearing change needs urgent ENT and specialist antiviral care.

Eczema herpeticumRed flag

Sudden monomorphic painful punched-out erosions over eczema with fever or malaise requires same-day systemic antiviral assessment.

Disseminated or neurological diseaseRed flag

Widespread vesicles, confusion, seizure, meningism, focal deficit or visceral symptoms in herpesvirus infection is an emergency.

Red flags requiring action

Ocular symptoms, Hutchinson sign, neurological deficit, meningism, disseminated lesions, eczema herpeticum, pregnancy near delivery with genital lesions, neonatal exposure or severe immunocompromise requires urgent specialist care.

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
Vesicle-base HSV and VZV PCRFirst step
Why
Distinguish herpes viruses in atypical, severe, genital or immunocompromised presentations.
Interpretation and limitations
Unroof a fresh vesicle and swab the cellular base; an old crust or previous antiviral treatment reduces yield.
02
Visual acuity and ocular examination
Why
Identify sight-threatening keratitis, uveitis or orbital involvement.
Interpretation and limitations
Do not use a negative fluorescein examination in primary care to delay ophthalmology when pain, photophobia or visual change persists.
03
Immune and pregnancy assessment
Why
Determine dissemination risk, antiviral route and contact precautions.
Interpretation and limitations
Review malignancy, HIV risk with consent, immunomodulators, transplantation and pregnancy; severe disease may be the first immune-suppression clue.
04
Renal function
Why
Dose aciclovir or valaciclovir safely in older, dehydrated or renally impaired patients.
Interpretation and limitations
Use current eGFR and clinical hydration; neurotoxicity or crystal nephropathy can emerge when dose is not adjusted.
05
CSF PCR and neuroimaging
Why
Investigate suspected encephalitis, meningitis or vasculopathy under emergency care.
Interpretation and limitations
Start intravenous aciclovir immediately when encephalitis is suspected; testing must not delay treatment.

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

Impetigo

Honey crust and superficial fragile bullae without a recurrent prodrome favour bacterial infection, though herpes erosions can become secondarily impetiginised.

Contact dermatitis

An exposure-shaped itchy vesicular field usually lacks grouped painful lesions and a neural or recurrent distribution.

Dermatitis herpetiformis

Intensely itchy symmetrical grouped lesions on extensor surfaces with gluten-sensitive enteropathy differ from painful unilateral zoster.

Bell palsy and stroke

Facial weakness needs neurological localisation; ear vesicles and pain suggest Ramsay Hunt, while limb or speech deficits demand stroke assessment.

Genital ulcer causes

Syphilis, aphthosis, trauma and inflammatory disease require sexual-health history and testing when genital ulcer morphology or course is atypical.

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

01Uncomplicated eligible zosterTreat early and control painFirst stepA unilateral dermatomal eruption is within 72 hours and age, severity, site or host risk meets antiviral criteria.

1Check eye, ear, neurological and dissemination features, pregnancy, immunity, renal function and medicines.
2Start aciclovir 800 mg five times daily or valaciclovir 1 g three times daily for seven days with renal adjustment and hydration advice.
3Provide stepped analgesia, cover lesions and review new vesicles, eye symptoms, weakness or uncontrolled pain promptly.

02High-risk herpesvirus diseaseEscalate sight or life threatsEscalationOcular, neurological, disseminated, neonatal, pregnancy-related or severe immunocompromised disease is possible.

1Arrange same-day ophthalmic, emergency, sexual-health, obstetric or infectious-diseases review according to the threatened organ and host.
2Take suitable lesion, blood or CSF samples without delaying indicated systemic or intravenous aciclovir.
3Apply airborne or contact precautions as locally required and coordinate susceptible-contact management with infection specialists or UKHSA.

03Recurrent HSVMatch episodic or suppressive careTypical HSV recurs and frequency, severity, transmission or personal impact justifies active treatment.

1Confirm the phenotype and site, offer sexual-health testing for genital disease and identify ocular, pregnancy or immune red flags.
2Begin episodic antiviral treatment during prodrome or the first lesions using the site-specific licensed regimen, or discuss suppression for frequent burdensome recurrence.
3Review adherence, renal function, trigger management, partner communication and whether persistent ulcers need PCR, resistance testing or diagnostic reassessment.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

A first-line systemic antiviral for eligible shingles and a component of specialist HSV regimens.

Aciclovir tablets

For herpes zoster take 800 mg orally five times daily at approximately four-hour intervals while awake for seven days.

Reduce dose in renal impairment, maintain hydration, review neurotoxicity and nephrotoxic medicines, and use intravenous treatment for severe disseminated or neurological disease.

A better-absorbed alternative that simplifies oral zoster dosing and can support adherence.

Valaciclovir tablets

For herpes zoster take 1 g orally three times daily for seven days, adjusted for renal function.

Check kidney function, hydration, age and neurological symptoms; high exposure can cause confusion, hallucinations or renal injury.

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

Herpes keratitis and uveitis

Corneal infection can scar and reduce vision; topical corticosteroid without ophthalmic supervision can worsen epithelial HSV.

Post-herpetic neuralgia

Pain persisting after rash resolution increases with age and severe acute pain and can disrupt sleep, mood and function.

Encephalitis and meningitis

HSV encephalitis and VZV meningoencephalitis can present with confusion, seizures, meningism or focal signs and require immediate intravenous therapy.

Eczema herpeticum

Disseminated HSV over atopic skin causes monomorphic punched-out erosions, fever and possible ocular or systemic spread.

Motor and cranial neuropathy

Zoster can cause facial palsy, hearing loss, urinary retention or segmental weakness depending on affected ganglion and nerve.

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

Confirm that new vesicle formation and systemic symptoms cease; reconsider diagnosis or immunity when lesions continue despite correctly dosed therapy.
Ask about eye pain, photophobia, vision, hearing, facial movement, urinary retention, weakness, confusion and severe headache at follow-up.
Review renal function and hydration in older, unwell or renally impaired patients and reduce antiviral dose according to current product guidance.
Track acute pain and sleep, then assess persistent neuropathic pain after healing and treat post-herpetic neuralgia through its dedicated pathway.
For recurrent genital HSV, review transmission counselling, pregnancy plans, frequency and whether episodic or suppressive treatment still meets patient goals.

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

Zoster transmits chickenpox

A susceptible contact exposed to vesicle fluid develops primary varicella, not shingles, which is endogenous reactivation.

Nasal tip raises risk

Hutchinson sign indicates nasociliary involvement but its absence does not exclude ocular disease when symptoms are present.

Pain can precede rash

Pre-eruptive zoster neuralgia can mimic renal, cardiac or musculoskeletal pain before the dermatome declares itself.

Fresh vesicles sample best

PCR yield is highest from cells at a newly unroofed vesicle base rather than a dry late crust.

Never improvise ocular steroid

Topical corticosteroid in herpetic eye disease requires ophthalmic diagnosis and concurrent antiviral strategy.

11Common pitfallsFrequent interpretation and management errors.

01
Reassuring a patient with forehead zoster despite eye pain because the cornea looks normal without specialist equipment.
02
Withholding antiviral treatment from evolving high-risk zoster solely because 72 hours has passed.
03
Prescribing full-dose aciclovir without checking renal function in a frail dehydrated older adult.
04
Calling monomorphic punched-out erosions on eczema bacterial impetigo and delaying systemic antiviral treatment.
05
Telling contacts they can catch shingles rather than explaining transmission of primary chickenpox from uncovered vesicles.