About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
Key points
- HSV-1: primarily orolabial. HSV-2: primarily genital. Increasing HSV-1 genital infection
- Primary infection more severe (gingivostomatitis). Recurrences milder
- Grouped vesicles on erythematous base that crust over. Prodromal tingling
- Aciclovir 200 mg 5x daily for 5 days (primary) or 400 mg TDS for 5 days (recurrence)
- Eczema herpeticum: punched-out erosions in eczema patient — EMERGENCY, IV aciclovir
Overview
HSV causes recurrent mucocutaneous infections. After primary infection, virus establishes latency in sensory ganglia (trigeminal for orolabial, sacral for genital) and reactivates periodically. HSV-1 is now the commonest cause of primary genital herpes in young adults in the UK. Asymptomatic shedding allows transmission.
Epidemiology
HSV-1 seroprevalence ~50-70% in UK adults. HSV-2 ~10-15%. Many infections subclinical. Genital herpes is one of the most common STIs. Neonatal herpes rare but devastating (mortality ~30% untreated).
Clinical Features
Symptoms
Primary orolabial: painful gingivostomatitis with extensive ulceration and fever
Recurrent: prodromal tingling then grouped vesicles on lip (cold sore)
Primary genital: painful vesicles/ulcers, dysuria, inguinal lymphadenopathy
Eczema herpeticum: rapidly worsening eczema with punched-out erosions
HSV encephalitis: fever, headache, seizures, altered consciousness
Signs
Grouped vesicles on erythematous base — classic appearance
Vesicles rupture to shallow painful ulcers that crust
Herpetic whitlow: vesicles on finger
Eczema herpeticum: monomorphic punched-out erosions on eczematous skin
Investigations
First-line
Clinical diagnosisGrouped vesicles in characteristic location
Viral swab (HSV PCR)Swab base of fresh vesicle — most sensitive, types HSV-1 vs 2
Specialist
CSF HSV PCRIf encephalitis suspected — do NOT delay aciclovir for LP
Management
BASHH Guidelines + NICE CKS1
Primary orolabial
- Aciclovir 200 mg 5x daily for 5-7 days (within 72 hours)
- Supportive: analgesia, hydration
2
Recurrent (cold sores)
- Mild: topical aciclovir 5% cream 5x daily for 5 days at prodrome
- Frequent: oral aciclovir 400 mg BD as suppressive therapy
3
Genital herpes
- Primary: aciclovir 400 mg TDS or valaciclovir 500 mg BD for 5 days
- Suppressive (>=6 recurrences/year): aciclovir 400 mg BD continuously
4
Eczema herpeticum — EMERGENCY
- IV aciclovir 5-10 mg/kg TDS
- STOP all topical corticosteroids and calcineurin inhibitors
Complications
- Eczema herpeticum: Dermatological emergency — can disseminate
- HSV encephalitis: Temporal lobe predilection, ~70% mortality untreated
- Neonatal herpes: Acquired during delivery — high mortality
- Erythema multiforme: ~50% of EM triggered by HSV
- Keratitis: Dendritic ulcer on fluorescein — ophthalmology emergency
UKMLA Exam Tips
- 1Grouped vesicles on erythematous base = HSV until proven otherwise
- 2Eczema herpeticum: punched-out erosions + eczema + unwell = IV aciclovir + STOP steroids
- 3HSV encephalitis: temporal lobe — do NOT delay aciclovir for investigations
- 4Herpetic whitlow: do NOT incise (risk of superinfection)
- 5Erythema multiforme target lesions — ~50% triggered by HSV, not drugs
- 6HSV-1 is now commonest cause of primary genital herpes in young UK adults
practicetest your knowledge on Herpes SimplexApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — Dermatology and beyond.
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